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IC produce time ?

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Bulent UNALMIS

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Jul 7, 1997, 3:00:00 AM7/7/97
to

Hello,

I want to learn,

How long time to produced one SSI IC at the factory?

(for example 74LS00 )

one second, one minute, one hour ? ....


Thanks.

William L. Bahn

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Jul 8, 1997, 3:00:00 AM7/8/97
to

Probably many days. It doesn't take a whole lot less time than it takes to
make a Pentium. The difference comes not in how long it takes to make one,
but in how many you can make at one time. Plus the difference in the
capital costs required to make the masks and perform the processing at the
finer resolution of a VLSI chip compared to an SSI chip.

Because ICs are batch manufactured, the proper question is how many SSI
chips can a factory produce per day (on a dedicated line). Translating this
to time per one IC is an interesting figure, but it has little physical
meaning.

If you really want to know the answer, I would recommend calling National
Semiconductor or Motorola or Joe's IC House and All-night Video Rental and
ask to speak with someone at their wafer fab facility. I'd wager you'll get
more information than you wanted with only a few phone calls.

Bulent UNALMIS <una...@club-internet.fr> wrote in article
<33C127...@club-internet.fr>...

Nicholas Gray

unread,
Jul 9, 1997, 3:00:00 AM7/9/97
to una...@club-internet.fr

Bulent UNALMIS wrote:
>
> Hello,
>
> I want to learn,
>
> How long time to produced one SSI IC at the factory?
>
> (for example 74LS00 )
>
> one second, one minute, one hour ? ....
>
> Thanks.

The time to make an IC is not an easy question to answer because there
are delays in a practical system. You can consider this as an estimate:
4 to 6 weeks - Wafer Fabrication
1 to 6 days - Electrical test of wafers
3 to 5 days - Shipping to assembly plant
1 to 6 days - Packaging operations
1 to 8 days - Final testing & QA operations
3 to 5 days - Ship to wherehouse

You can see that the total time comes to about 6 to 12 weeks. The
shorter time is, generally, used for expedited product, while the longer
time is mor for standard times. Expediting product is expensive because
the special handling means that something else is not done with other
product on time. The time gained on the expedited lot is much less than
the time lost on displaced lots. An example would be taking down a
currently running setup to get an expedited lot going, then going back
to the old setup when the expedited lot is completed. Two setups are
then done on a single lot when one would have been done if it were not
for the expedite. How long a setup takes depends on the complexity of
the particular operation and, in some cases, can take well over an hour.
Imagine an expedited lot interrupting various other lots at many, many
stages of operation (nearly 20 fabrication steps, in some cases, for a
start!)

Not included in these times are scheduling delays, which can add another
one to three weeks. And the total time could be a LOT longer than 12
weeks it the demand far exceeds supply and manufacturing capacity. Ever
hear of 26 to 52 week delivery quotes? It is unusual, but it does
happen.

Realize that an IC house does not make one IC at a time. There are
usually hundreds to thousands of ICs on a single wafer, depending upon
wafer size and die size. A "small" wafer run would be about 8 wafers
started through fabrication, while a normal run would be 12 to 24
wafers, depending upon the manufacturer and process capabilities.

When it comes to assembly and test, a single wafer might be assembled if
a relatively small quantity is needed.

I am sorry that this is necessarily short, but I am very busy now. I do
hope, however, that this gives you and others some insight as to what
happens at an IC house. I think it a minor miracle that we can sell some
of the products for as little as we do.

--
Nick Gray
Applications Engineer
National Semiconductor Corporation
email: ng...@redwood.nsc.com
National Data Sheets at http://www.national.com

Mike

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Jul 10, 1997, 3:00:00 AM7/10/97
to

Nicholas,

Sorry to tag on a previous posting, but there is a discussion of zener
diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
LM337 regulator Spice Model"

I was wondering if you could shed any light on this phenomenon?

Mike

Bob Wilson

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Jul 11, 1997, 3:00:00 AM7/11/97
to

In article <33C585...@Today.Thanks>, NoS...@Today.Thanks writes...

It's actually pretty basic.
As is well known, reverse biased diode exhibit voltage variable capacitance.
Couple this with stray circuit inductance and you have the beginnings of an
LC oscillator. And not a very predictable one either.

Bob.


Nicholas Gray

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Jul 14, 1997, 3:00:00 AM7/14/97
to Mike

Mike wrote:
>
> Nicholas,
>
> Sorry to tag on a previous posting, but there is a discussion of zener
> diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
> LM337 regulator Spice Model"
>
> I was wondering if you could shed any light on this phenomenon?
>
> Mike

Mike,
I would need more information on the circuit to make a response. In
general, zeners do not oscillate, regardless of what was said on another
posting. Perhaps the author meant to say something else, I do not know.
However, the circuit a zener is used in can oscillate, depending upon a
number of factors. The more you can tell me about the circuit, the more
likely it is that I can help.

Mike Monett

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Jul 14, 1997, 3:00:00 AM7/14/97
to

Nicholas Gray wrote:

> Mike wrote:

> > Nicholas,

> > Sorry to tag on a previous posting, but there is a discussion of zener
> > diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
> > LM337 regulator Spice Model"

> > I was wondering if you could shed any light on this phenomenon?

> > Mike

> Mike,
> I would need more information on the circuit to make a response. In
> general, zeners do not oscillate, regardless of what was said on another
> posting. Perhaps the author meant to say something else, I do not know.
> However, the circuit a zener is used in can oscillate, depending upon a
> number of factors. The more you can tell me about the circuit, the more
> likely it is that I can help.

> Nick Gray


> Applications Engineer
> National Semiconductor Corporation
> email: ng...@redwood.nsc.com
> National Data Sheets at http://www.national.com

Thank you for responding to my query, Nick - I have never seen a zener
oscillate either.

Intermittent connections, faulty test equipment, radiation from nearby
WaveTek bench oscillators, parasitic oscillations in transistors and IC's
- anything with gain, old-style radar with square envelopes, magnetic
fields from SCR power equipment, and on, and on.

Never seen a zener oscillate. I don't say it's impossible - anything is
possible in electronics and semiconductors.

But I have no success to get any more information on this phenomenon.
Hopefully, one poster will send me some samples - maybe if these show it,
you could help us track it down?

Thanks for your help.

Best Regards,

Michael R. Monett, mailto:a...@csolve.net

Bob Wilson

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Jul 15, 1997, 3:00:00 AM7/15/97
to

In article <33CA61...@redwood.nsc.com>, ng...@redwood.nsc.com writes...

>
>Mike wrote:
>>
>> Nicholas,
>>
>> Sorry to tag on a previous posting, but there is a discussion of zener
>> diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
>> LM337 regulator Spice Model"
>>
>> I was wondering if you could shed any light on this phenomenon?
>>
>> Mike
>
>Mike,
>I would need more information on the circuit to make a response. In
>general, zeners do not oscillate, regardless of what was said on another
>posting. Perhaps the author meant to say something else, I do not know.
>However, the circuit a zener is used in can oscillate, depending upon a
>number of factors. The more you can tell me about the circuit, the more
>likely it is that I can help.

I think the idea in previous posts was that zeners can be a part of an
unintentional oscillating system. Not very surprising, actually, given their
voltage-variable capacitance. But clearly they are not an oscillator unto
themselves. It seems, however, that some respondents to this thread are too
deeply mired in the alternate reality of Spice and other computer games to
notice the goings on in the real world (or the lab bench as the case may be).

Bob.


Mike

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Jul 15, 1997, 3:00:00 AM7/15/97
to

Bob Wilson wrote:
>
> In article <33C585...@Today.Thanks>, NoS...@Today.Thanks writes...
> >
> >Nicholas,
> >
> >Sorry to tag on a previous posting, but there is a discussion of zener
> >diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
> >LM337 regulator Spice Model"
> >
> >I was wondering if you could shed any light on this phenomenon?
>
> It's actually pretty basic.
> As is well known, reverse biased diode exhibit voltage variable capacitance.
> Couple this with stray circuit inductance and you have the beginnings of an
> LC oscillator. And not a very predictable one either.
>
> Bob.

Well, to oscillate, the gain around the loop must be greater than unity.
Your post does not explain how this happens.

The internal capacitance of a zener in avalanche mode is several hundred
picofarads. The claimed oscillation is in the VHF range.

The inductance required is less than the distance between the connections
to the zener.

Your post does not explain how this violation is satisfied.

If you have measurements, calculations, or supportable theory, then I'd
like to hear it.

If you only have FUD, confusion, or just want to get it off, then join
another group.

Mike

Gregory T Freitag

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Jul 15, 1997, 3:00:00 AM7/15/97
to


Mike Monett <a...@csolve.net> wrote in article <33CAED...@csolve.net>...


> Nicholas Gray wrote:
>
> > Mike wrote:
>

> > > Nicholas,
>
> > > Sorry to tag on a previous posting, but there is a discussion of
zener
> > > diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
> > > LM337 regulator Spice Model"

I saw Bob Pease about a month ago, I think he would put this one under "
How do you know when your computer is lying to you ", any aspiring engineer
who thinks Spice is the best thing since spiced bread would do themselves a
favor to read his book " Troubleshooting Analog Circuits ".


Greg

Bob Wilson

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Jul 15, 1997, 3:00:00 AM7/15/97
to

In article <33CB30...@Today.Thanks>, NoS...@Today.Thanks writes...

>
>Bob Wilson wrote:
>>
>> In article <33C585...@Today.Thanks>, NoS...@Today.Thanks writes...
>> >
>> >Nicholas,
>> >
>> >Sorry to tag on a previous posting, but there is a discussion of zener
>> >diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
>> >LM337 regulator Spice Model"
>> >
>> >I was wondering if you could shed any light on this phenomenon?
>>
>> It's actually pretty basic.
>> As is well known, reverse biased diode exhibit voltage variable
>> capacitance.
>> Couple this with stray circuit inductance and you have the beginnings of
>> an LC oscillator. And not a very predictable one either.
>>
>> Bob.
>
>Well, to oscillate, the gain around the loop must be greater than unity.
>Your post does not explain how this happens.

I supposse you would have to look at the rest of the associated circuit,
wouldn't you?

>The internal capacitance of a zener in avalanche mode is several hundred
>picofarads. The claimed oscillation is in the VHF range.

Actually, it can easily be less than that, since the actual value is a
function of reverse voltage and zener die size. With fairly high voltage
zeners (say, an 18 Volt zener), and using a small 400 mW type, the
capacitance can be a lot less than that. Couple this with a nanohenry or so
lead inductance and VHF range resonance is quite possible. 50 pF with 1 nH
resonates at around 700 MHz.

>The inductance required is less than the distance between the connections
>to the zener.
>
>Your post does not explain how this violation is satisfied.

A nH represents a reasonable amount of wire, Longer than any zener leads I
know of.

>If you have measurements, calculations, or supportable theory, then I'd
>like to hear it.
>
>If you only have FUD, confusion, or just want to get it off, then join
>another group.

Ooooh! Nasty!

Bob.


Mike

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Jul 15, 1997, 3:00:00 AM7/15/97
to

Bob Wilson wrote:
>
> In article <33CA61...@redwood.nsc.com>, ng...@redwood.nsc.com writes...
> >
> >Mike wrote:
> >>
> >> Nicholas,
> >>
> >> Sorry to tag on a previous posting, but there is a discussion of zener
> >> diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
> >> LM337 regulator Spice Model"
> >>
> >> I was wondering if you could shed any light on this phenomenon?
> >>
> >> Mike
> >
> >Mike,
> >I would need more information on the circuit to make a response. In
> >general, zeners do not oscillate, regardless of what was said on another
> >posting. Perhaps the author meant to say something else, I do not know.
> >However, the circuit a zener is used in can oscillate, depending upon a
> >number of factors. The more you can tell me about the circuit, the more
> >likely it is that I can help.
>
> I think the idea in previous posts was that zeners can be a part of an
> unintentional oscillating system. Not very surprising, actually, given their
> voltage-variable capacitance. But clearly they are not an oscillator unto
> themselves. It seems, however, that some respondents to this thread are too
> deeply mired in the alternate reality of Spice and other computer games to
> notice the goings on in the real world (or the lab bench as the case may be).
>
> Bob.

Get off it - produce calculations, demonstrable theory, explanations that
work - or get off this newsgroup.

Mike

Mike

unread,
Jul 15, 1997, 3:00:00 AM7/15/97
to

Mike Monett wrote:


>
> Nicholas Gray wrote:
>
> > Mike,
> > I would need more information on the circuit to make a response. In
> > general, zeners do not oscillate, regardless of what was said on another
> > posting. Perhaps the author meant to say something else, I do not know.
> > However, the circuit a zener is used in can oscillate, depending upon a
> > number of factors. The more you can tell me about the circuit, the more
> > likely it is that I can help.
>

> > Nick Gray
> > Applications Engineer
> > National Semiconductor Corporation
> > email: ng...@redwood.nsc.com
> > National Data Sheets at http://www.national.com

[...]

Sorry to bother you Nick - recent postings show it was nothing more than
a troll.

Thanks for responding - I hope next time is more interesting.

Mike

Andy Borsa

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Jul 16, 1997, 3:00:00 AM7/16/97
to

Mike wrote:

>
> Bob Wilson wrote:
> >
> > I think the idea in previous posts was that zeners can be a part of an
> > unintentional oscillating system. Not very surprising, actually, given their
> > voltage-variable capacitance. But clearly they are not an oscillator unto
> > themselves. It seems, however, that some respondents to this thread are too
> > deeply mired in the alternate reality of Spice and other computer games to
> > notice the goings on in the real world (or the lab bench as the case may be).
> >
> > Bob.
>
> Get off it - produce calculations, demonstrable theory, explanations that
> work - or get off this newsgroup.
>
> Mike

A voltage variable capacitance, when correctly embedded in some circuit
and pumped with a suitable RF source, will in fact exhibit negative
resistance just like an oscillator. Can be used for all sorts of
interesting things. Ever hear of a parametric amplifier or converter?

IEEE pubs back in the 40's, 50's, and 60's can be searched for
theoretical papers.

And yes, it can be modelled and simulated in good ole spice.

---------------------------------------------
Andy Borsa RF/Wireless Design Consultant
Real Address: an...@moose.mv.com
---------------------------------------------

Bob Wilson

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Jul 16, 1997, 3:00:00 AM7/16/97
to

In article <33CB45...@Today.Thanks>, NoS...@Today.Thanks writes...
>
>Bob Wilson wrote:

>Get off it - produce calculations, demonstrable theory, explanations that
>work - or get off this newsgroup.

Ja voll, Herr Obergrueppenfueher!!! I had no idea we had a new dictator here.

Bob.


Bill Sloman

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Jul 17, 1997, 3:00:00 AM7/17/97
to

<snip>


>
>Get off it - produce calculations, demonstrable theory, explanations that
>work - or get off this newsgroup.

This is *sci*.electronics.design. This means that calculations, theory,
and explanations that work, are all aimed at explaining and controlling
(as best we can) what goes on in the real world.

If Spice can't explain the infrequent, but clearly attested appearance
of high frequency oscillations across a zener diode in any otherwise
passive circuit, so much the worse for Spice. The information that this
can happen is clearly useful, and the apparent inability of Spice models
to simulate this phenomenon is an example of why you can't 100% rely on
simulation in designing a new circuit - which is why I adduced the example
in the first place.

If you can't understand this fairly elementary point, maybe *you* should
get off this newsgroup. Bob Wilson is a well established and useful
contributer to the newgroup, and I can't say the same for you.

Bill Sloman (slo...@sci.kun.nl) | Precision analog design
TZ/Electronics, Science Faculty, | Fast analog design and layout
Nijmegen University, The Netherlands | Very fast digital design/layout
| e-mail for rates and conditions.

Keith Lockstone

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Jul 17, 1997, 3:00:00 AM7/17/97
to

Bill Sloman wrote:
>
> <snip>

> This is *sci*.electronics.design. This means that calculations, theory,
> and explanations that work, are all aimed at explaining and controlling
> (as best we can) what goes on in the real world.

When looking closely at zener characteristics in the low current region
(1-25uA) I have seen a small negative resistance region. This may cause
oscillation - cf tunnel diodes. I think it rather unlikely though.

Keith.

Mike McCarty

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Jul 17, 1997, 3:00:00 AM7/17/97
to

In article <33C585...@Today.Thanks>, Mike <NoS...@Today.Thanks> wrote:
)Nicholas,
)
)Sorry to tag on a previous posting, but there is a discussion of zener
)diodes going into oscillation in the thread "Re: LM138, LM338, LM117,
)LM337 regulator Spice Model"
)
)I was wondering if you could shed any light on this phenomenon?
)
)Mike

The ICs you mention are not Zener diodes. They contain amplifiers.

Mike
--
----
char *p="char *p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
I don't speak for DSC. <- They make me say that.

Mike

unread,
Jul 20, 1997, 3:00:00 AM7/20/97
to

Bill Sloman wrote:
>
> <snip>
> >
> >Get off it - produce calculations, demonstrable theory, explanations that
> >work - or get off this newsgroup.
>
> This is *sci*.electronics.design. This means that calculations, theory,
> and explanations that work, are all aimed at explaining and controlling
> (as best we can) what goes on in the real world.
>
> If Spice can't explain the infrequent, but clearly attested appearance
> of high frequency oscillations across a zener diode in any otherwise
> passive circuit, so much the worse for Spice. The information that this
> can happen is clearly useful, and the apparent inability of Spice models
> to simulate this phenomenon is an example of why you can't 100% rely on
> simulation in designing a new circuit - which is why I adduced the example
> in the first place.
>
> If you can't understand this fairly elementary point, maybe *you* should
> get off this newsgroup. Bob Wilson is a well established and useful
> contributer to the newgroup, and I can't say the same for you.

Hi Bill,

Thank you for the excellent posting.

This newsgroup is sci.electronics.design - the thread about
oscillating zeners is not.

There is very little serendipity in semiconductors. The
possibility of some action is first theorized, then a great deal
of money and effort is expended to make it happen, and find out
all the reasons why the effect doesn't work as well as it should.

It is highly unlikely that the possibility of oscillating zeners
would have gone unnoticed by the semiconductors engineers and
scientists, but be noticed by a few individuals on a newsgroup.

There is not one single URL describing this phenomenon on the
web.

There is not one single application note at National
Semiconductor, Motorola, or any other company that produces
semiconductors.

There is not one single reference in the IEEE, MIT, or Berkeley
papers.

IBM would have patents on it - there are none.

Bob Pease has no article describing this highly unusual
phenomenon, or how to improve on it.

Steve Garcia does not describe it in the Circuit Cellar.

It is not described in The Art of Electronics.

It doesn't exist. There are plenty of ways that surrounding
circuitry could show oscillations, but this is no reason to
attribute it to the zener.

Zeners are manufactured in very large quantities.

No one can produce a sample of a zener that oscillates.

If such a phenomenon were possible, the semiconductor
manufacturers would be all over you like flies on honey trying to
get one, or track down the cause.

Think of the possibilities - zeners are much cheaper to
manufacture than Gunn, tunnel or Impatt diodes.

If a zener could oscillate, there would be no need for varactors
and separate components to make a high-frequency oscillator.

The person who first demonstrated the existence of oscillations
in zeners would be up for the Nobel prize. Easki did it with the
tunnel diode - why not a zener.

The first sightings are claimed to be 20 or 30 years ago - if it
were possible, it would be in the mainstream of semiconductors by
now.

Unfortunately, semiconductor physics doesn't work that way. If a
zener could oscillate, we would see plenty of examples used
everywhere. We do not.

The people who report sightings of oscillating zeners claim it
was some time ago - before they learned much about electronics,
and before they should have learned it is highly unlikely.

Apparently, they never did. Thus, they are unable to separate
fact from fiction, and are good candidates for theories on UFO's,
the Bermuda Triangle, and the lost city of Atlantis.

That they do not know such a dividing line exists leave room for
doubt on the credibility of their postings. The fact they cross
the line into fantasy leaves little doubt about their competence.

To claim that one application engineer recommended placing a 1000
pf cap across a zener to cure it is incredible. To claim that two
app engineers made the same suggestion is fantasy. To claim that
a competent engineer accepted this answer is silly.

Where are the app notes from these companies describing this
cure?

Give me one URL, one reference, one app note, or one sample -
that's all I asked for in the beginning, and that's all I ask for
now.

Failing that, it's a safe bet the only place oscillating zeners
exist is as power sources for UFO's.

Mike

ma...@global.california.com

unread,
Jul 20, 1997, 3:00:00 AM7/20/97
to Keith Lockstone

Is this really oscillation or just the extremely noisy region of operation
exciting external circuit resonances (including the zener's package)

- Robert -

On Thu, 17 Jul 1997, Keith Lockstone wrote:

> Bill Sloman wrote:
> >
> > <snip>


>
> > This is *sci*.electronics.design. This means that calculations, theory,
> > and explanations that work, are all aimed at explaining and controlling
> > (as best we can) what goes on in the real world.
>

John Woodgate

unread,
Jul 20, 1997, 3:00:00 AM7/20/97
to

In article <Pine.BSI.3.95.970720113659.26834F-
100...@global.california.com>, ma...@global.california.com writes

>Is this really oscillation or just the extremely noisy region of operation
>exciting external circuit resonances (including the zener's package)
>
> - Robert -

Well, that's an intelligent question, but you must realise that Mike
Spam has said that zeners don't oscillate, so we shouldn't really
discuss the subject any more in deference to his omniscience.

It is quite possible that in some cases the avalanche noise does excite
the resonance between lead inductance and diode capacitance - it must,
after all, to some extent. This would result in observable 'oscillation'
if the Q were high enough, and swamping the diode capacitance with a
shunt capacitor might well remove the effect. However, there are reports
also of an observable negative resistance region in the charatceristics
of some diodes, which _would_ provoke basically relaxation oscillations,
probably also spectrally enhanced by stray resonances. This form of
oscillation might well be resistant to shunting the diode with a
capacitor.

>On Thu, 17 Jul 1997, Keith Lockstone wrote:
>
>> Bill Sloman wrote:
>> >
>> > <snip>
>>
>> > This is *sci*.electronics.design. This means that calculations, theory,
>> > and explanations that work, are all aimed at explaining and controlling
>> > (as best we can) what goes on in the real world.
>>
>> When looking closely at zener characteristics in the low current region
>> (1-25uA) I have seen a small negative resistance region. This may cause
>> oscillation - cf tunnel diodes. I think it rather unlikely though.
>>
>> Keith.
>>
>>
>

--
Regards, John Woodgate. Phone +44 (0)1268 747839
Fax +44 (0)1268 777124. OOO - Own Opinions Only
Alternative e-mail: jm...@thenet.co.uk
That means I get double spam with everything (>>8-(

Mike

unread,
Jul 21, 1997, 3:00:00 AM7/21/97
to

Gregory T Freitag wrote:
>
> Mike Monett <a...@csolve.net> wrote in article <33CAED...@csolve.net>...
> > Nicholas Gray wrote:
> >
> > > Mike wrote:

<...>

> I saw Bob Pease about a month ago, I think he would put this one under "
> How do you know when your computer is lying to you ", any aspiring engineer
> who thinks Spice is the best thing since spiced bread would do themselves a
> favor to read his book " Troubleshooting Analog Circuits ".
>
> Greg
>

Well Greg - is this straight from the horse's mouth? Nice of you
to do Bob's thinking for him, then pass your own mangled version
along to the rest of us. I think it's called name-dropping.

I don't understand your anti-SPICE attitude, especially in an
electronics design newsgroup. I certainly wouldn't want to work
in any company silly enough to hire you, or buy any of its
products.

SPICE is an invaluable tool for all aspects of critical analog
and high-speed digital design. Just with any tool - you have to
learn how to use it and respect it's limits. There are many
useful demos available for free - and most of them work well.

The best engineers are skilled with any tool that can help them
do their job. Often, SPICE is the only way to solve a critical
engineering problem or to gain insight into the operation of a
circuit. In many companies, you are at a severe disadvantage if
you do not know SPICE.

You would have a difficult time trying to persuade some of the
top engineers on the planet to give up SPICE and go back to using
a slide rule.

It is incomprehensible that you would try to give anyone such
poor advice if you knew how to use SPICE yourself. Clearly, you
do not.

Good luck on your next job hunt!

Mike

Keith Lockstone

unread,
Jul 21, 1997, 3:00:00 AM7/21/97
to
ZEN.TXT

slo...@sci.kun.nl

unread,
Jul 21, 1997, 3:00:00 AM7/21/97
to

In article <33D1BF...@Today.Thanks>,
Mike <NoS...@Today.Thanks> wrote:

<snipped reprint of earlier message>


>
> This newsgroup is sci.electronics.design - the thread about
> oscillating zeners is not.

An assertion, rather poorly supported by what followed

> There is very little serendipity in semiconductors. The
> possibility of some action is first theorized, then a great deal
> of money and effort is expended to make it happen, and find out
> all the reasons why the effect doesn't work as well as it should.

There is very little serendipity anywhere, least of all where people
assert the impossibility of a phenomenon on the basis of an unimaginative
literature search.

> It is highly unlikely that the possibility of oscillating zeners
> would have gone unnoticed by the semiconductors engineers and
> scientists, but be noticed by a few individuals on a newsgroup.

<snipped list of places searched>

> It doesn't exist. There are plenty of ways that surrounding
> circuitry could show oscillations, but this is no reason to
> attribute it to the zener.
>
> Zeners are manufactured in very large quantities.
>
> No one can produce a sample of a zener that oscillates.
>
> If such a phenomenon were possible, the semiconductor
> manufacturers would be all over you like flies on honey trying to
> get one, or track down the cause.
>
> Think of the possibilities - zeners are much cheaper to
> manufacture than Gunn, tunnel or Impatt diodes.
>
> If a zener could oscillate, there would be no need for varactors
> and separate components to make a high-frequency oscillator.

If a zener were optimised for high frequency oscillation, it would
presumably be an IMPATT diode, and correspondinglyly harder to make, and
more expensive to buy.

> The person who first demonstrated the existence of oscillations
> in zeners would be up for the Nobel prize. Easki did it with the
> tunnel diode - why not a zener.

Not the Nobel Prize committee's finest hour ...

> The first sightings are claimed to be 20 or 30 years ago - if it
> were possible, it would be in the mainstream of semiconductors by
> now.
>
> Unfortunately, semiconductor physics doesn't work that way. If a
> zener could oscillate, we would see plenty of examples used
> everywhere. We do not.

This is good polemic, but poor logic. A couple of people have reported
seeing negative resistance with some zener diodes at currents of about
10uA to 25uA. This would support oscillation in the right circuit. Such
an oscillation is not commercially interesting, so it is no surprise that
it hasn't been written up. The IMPATT diode would appear to be the
optimised form of the zener diode oscillator.

> The people who report sightings of oscillating zeners claim it
> was some time ago - before they learned much about electronics,
> and before they should have learned it is highly unlikely.

Note the drift from fact to - erroneous - hypothesis.

> Apparently, they never did. Thus, they are unable to separate
> fact from fiction, and are good candidates for theories on UFO's,
> the Bermuda Triangle, and the lost city of Atlantis.

But, I - for one - retain enough of my sceptical faculties to be
unconvinced that a mastery of Spice is the be-all and end-all of the
electronics, which the proposition that Mike<NoS...@Today.Thanks> was
touting in this thread.

> That they do not know such a dividing line exists leave room for
> doubt on the credibility of their postings. The fact they cross
> the line into fantasy leaves little doubt about their competence.

And where does that put Mike, with his blind belief in Spice?

> To claim that one application engineer recommended placing a 1000
> pf cap across a zener to cure it is incredible. To claim that two
> app engineers made the same suggestion is fantasy. To claim that
> a competent engineer accepted this answer is silly.

Not to mention his blind belief in the competence of application
engineers. The belief that an extra capacitor will cure any oscillation
is surprisingly wide-spread. I've seen them on the outputs of op amps,
where they reduced the amplitude of oscillation to a level where it was
hard to see.


> Where are the app notes from these companies describing this
> cure?

An application note on the use of zener diodes at 10-25uA? I can't
remember ever seeing any application note on zener diodes.

> Give me one URL, one reference, one app note, or one sample -
> that's all I asked for in the beginning, and that's all I ask for
> now.

Try searching under impact ionization avalanche transit time diodes.

> Failing that, it's a safe bet the only place oscillating zeners
> exist is as power sources for UFO's.

Nice line, but it could be a really expensive "safe" bet...

Bill Sloman, Nijmegen

-------------------==== Posted via Deja News ====-----------------------
http://www.dejanews.com/ Search, Read, Post to Usenet

Walter Gray

unread,
Jul 23, 1997, 3:00:00 AM7/23/97
to

In article <8694870...@dejanews.com>, slo...@sci.kun.nl writes:
>In article <33D1BF...@Today.Thanks>,
> Mike <NoS...@Today.Thanks> wrote:
[]

>> Where are the app notes from these companies describing this
>> cure?
>
>An application note on the use of zener diodes at 10-25uA? I can't
>remember ever seeing any application note on zener diodes.

Last year somebody posted a request for a zener that worked at these
currents, of course there was no answer. Manufacturers recommend
1mA or more and I doubt that any manufacturer could tell you how
their devices behaved at such low currents. They just don't bother
to characterise devices outside their normal envelope. Similarly
they don't seem to advise their customers about process changes that
might cause odd effects to appear.


[]


>> Failing that, it's a safe bet the only place oscillating zeners
>> exist is as power sources for UFO's.
>
>Nice line, but it could be a really expensive "safe" bet...

You should have asked for the money up front Bill :)

Walter


jedney

unread,
Jul 23, 1997, 3:00:00 AM7/23/97
to

Peter wrote:

> >When looking closely at zener characteristics in the low current
> region
> >(1-25uA) I have seen a small negative resistance region. This may
> cause
> >oscillation - cf tunnel diodes. I think it rather unlikely though.
>

> It is in fact common to see oscillation in a normal rectifier circuit,
>
> e.g. a bridge.
>
> Take any old mains power supply, i.e. a transformer followed by a
> bridge rectifier and a capacitor, and connect a scope to any of the
> four nodes of the rectifier. You should see small amplitude
> oscillation, a few mV at around several kHz.
>
> The frequency can be much higher, and this oscillation can have
> adverse impact on EMC performance of some products. It is not uncommon
>
> to find caps (e.g. 1000pF) across the diodes to damp this down. Have a
>
> look at a schematic of an old TV set.
>
> Your note about *low* current confirm what one sees with the
> rectifiers: the oscillation is present only during turn-on or turn-off
>
> of each diode.
>
> I have seen this many times, but never thought it was due to negative
> resistance. I just thought it must be caused by the rapid increase in
> the current, combined with all the inductances and capaticances in the
>
> rest of the circuit. But one cannot have oscillation without *some*
> negative resistance.
>
> Peter.
>
> Return address is invalid to help stop junk mail.
> E-mail replies to z...@digiserve.com.

Most likely you are experiencing the reverse recovery time of a
diode. This current is due to the charge stored in the PN junction.
Although reverse voltage bias may be immediately applied, the electrons
and holes must retransition and this creates a "oscillatory" current
surge that does ring due to the junction capacitance and lead
inductance, along with other parasitic impedances of your circuit.


Bob Wilson

unread,
Jul 23, 1997, 3:00:00 AM7/23/97
to

In article <33D30C...@Today.Thanks>, NoS...@Today.Thanks writes...

>
>Gregory T Freitag wrote:
>>
>> Mike Monett <a...@csolve.net> wrote in article
<33CAED...@csolve.net>...
>> > Nicholas Gray wrote:
>> >
>> > > Mike wrote:
>
><...>
>
>> I saw Bob Pease about a month ago, I think he would put this one under "
>> How do you know when your computer is lying to you ", any aspiring
engineer
>> who thinks Spice is the best thing since spiced bread would do themselves
a
>> favor to read his book " Troubleshooting Analog Circuits ".
>>
>> Greg
>>
>
> Well Greg - is this straight from the horse's mouth? Nice of you
> to do Bob's thinking for him, then pass your own mangled version
> along to the rest of us. I think it's called name-dropping.

Well, I think the little fella's jealous!

> I don't understand your anti-SPICE attitude, especially in an
> electronics design newsgroup. I certainly wouldn't want to work
> in any company silly enough to hire you, or buy any of its
> products.

You do not seem to understand. No one is anti Spice here. However,
*experienced* designers are also PRO-COMMON SENSE. It is the mark of a poor
designer that he is more interested in his tools than in the design itself.

> SPICE is an invaluable tool for all aspects of critical analog
> and high-speed digital design. Just with any tool - you have to
> learn how to use it and respect it's limits. There are many
> useful demos available for free - and most of them work well.

Spice is also an invaluable tool for young inexperienced engineers and
engineering wannabes that allows them to spend hours getting lead down the
garden path because they lack the intuitive understanding that experience
brings.

> The best engineers are skilled with any tool that can help them
> do their job. Often, SPICE is the only way to solve a critical
> engineering problem or to gain insight into the operation of a
> circuit. In many companies, you are at a severe disadvantage if
> you do not know SPICE.

Any idiot can learn Spice. Big hairy deal! But not any idiot can become a
good designer.

> You would have a difficult time trying to persuade some of the
> top engineers on the planet to give up SPICE and go back to using
> a slide rule.
>
> It is incomprehensible that you would try to give anyone such
> poor advice if you knew how to use SPICE yourself. Clearly, you
> do not.
>
> Good luck on your next job hunt!

No wonder you want to remain incommunicato with an address like
NoS...@Today.Thanks! With an arrogant attitude like you demonstrate I
wouldn't want any prospective employer to know my real email address either.

I have seen lots of young engineers come and get let go, who thought they
knew it all too, then demonstrated that while they may have been able to make
their Sparc Station sing and dance, they ended up costing the company big
money in lost time and designs that hadn't a hope of being practical.

It is the height of arrogance for an inexperienced engineer to assume that
anyone who doesn't rave wildly about cad tools, must somehow be a luddite. In
my case, like many people, I first used Spice 15 years ago when it ran on a
UNIX mainframe and took half the day to do its thing. But I am not so stupid
as to believe that the tools are more important than a designers ability. Of
the various patents I happen to have, not one of them can be attributed to
Spice, even though I use it on occasion where it is useful.

Assuming that Spice is needed to be a good EE is just about as stupid as
assuming that someone with a power chisel will be a better artist than
Michaelangelo, because all he had was a hammer and chisel.

Do us a favour. Keep a record of your of your foaming at the mouth, then have
a look at it in 10 years from now. I guarantee you will feel like a fool when
you read it.

Bob.


Mark Zenier

unread,
Jul 24, 1997, 3:00:00 AM7/24/97
to

In article <8694870...@dejanews.com>, <slo...@sci.kun.nl> wrote:
>In article <33D1BF...@Today.Thanks>,
> Mike <NoS...@Today.Thanks> wrote:
>> This newsgroup is sci.electronics.design - the thread about
>> oscillating zeners is not.
>
>An assertion, rather poorly supported by what followed
>
>> There is very little serendipity in semiconductors. The
>> possibility of some action is first theorized, then a great deal
>> of money and effort is expended to make it happen, and find out
>> all the reasons why the effect doesn't work as well as it should.
>
>There is very little serendipity anywhere, least of all where people
>assert the impossibility of a phenomenon on the basis of an unimaginative
>literature search.

Real unimaginative. Your later mention of application notes caused
me to dig out my old (1980) Motorola Zener Diode Manual. (And this
is just end user application information. A serious discussion of
this probably would be covered in some academic journal on solid
state physics back in the 1960's sometime. The web is useless for
finding serious information in that time frame).

In it there is a lovely drawing (fig 4-5) showing what the zener knee
looks like at low current.


something like

/
/
/
/
________/

Here's the related text

" Between the minimum current shown in Figure 4-4 and the leakage
currents, there is the "knee" region. The avlanche mechanism may not
occur simultaneously across the entire area of the P-N junction, but first
at one microscopic site, then at an increasing number of sites as further
voltage is applied. This action can be accounted for by the "microplasma
discharge theory" and correlates with several breakdown characteristics

An exaggerated view of the knee region is shown in Figure 4-5.
As can be seen, the breakdown or avalanche current does not increase
suddenly, but consists of a series of smoothly rising current vs voltage
increments each with a sudden breakpoint.

At the lowest point, the zener resistance (slope of the curve)
would test high, but as current continues to climb, the resistance
decreases. It is as though each discharge site has high resistance
with each succeeding site being in parallel until total resistance is
very small.

In addition to the resistive effects, the microplasmas may act
as noise generators. The exact process of manufacturing affects how high
the noise will be, but in any event there will be some noise at the knee,
and will diminish considerably as current is allowed to increase."


Comparing this with the diode models as described in Vladimirescu's
"The Spice Book" or Kielkowski's "Spice, Practical Device Modeling",
Spice's models look very simple minded with the use of a smooth
exponential simulation of the knee.

Mark Zenier mze...@eskimo.com mze...@netcom.com


Tony Williams

unread,
Jul 24, 1997, 3:00:00 AM7/24/97
to

In article <8694870...@dejanews.com>, <URL:mailto:slo...@sci.kun.nl>
wrote:

[big snip, Bill being sceptical about Spice]

> But, I - for one - retain enough of my sceptical faculties to be
> unconvinced that a mastery of Spice is the be-all and end-all of the
> electronics, which the proposition that Mike<NoS...@Today.Thanks> was
> touting in this thread.


All those being sceptical about 1001% reliance on computer
simulation of circuitswere right....

I just tried it on the bench and it looks as though a zener
diode does have a negative-resistance region(s) at low
currents.

Setup:- Variable supply, 0-28v, uAmmeter, 22k, zener. Scope
across the zener (79C10).

Results:- Caution, the oscillations were difficult to lock
for any length of time, so I had to snatch approx
view and measurements.

1. 0.5uA (yes 1/2uA!) oscillation started, 60mV pk-pk, -ve
switch followed by ramp upwards. Classic relaxation
oscillator picture... volts increase to a region of
neg-R, sudden discharge, ramps back up to the neg-R region
again.

2. 80uA, same shape, 100mV pk-pk approx.

3. 100uA, difficult to see, but flat sections top and bottom,
>100mV pk-pk, going squarish maybe.

4. 160/170uA oscillation getting intermittant/disappearing.

5. >170uA no oscillation.

--
[Tony Williams, Ledbury, Herefordshire, UK.---Pagewidth=64-----]


Winfield Hill

unread,
Jul 25, 1997, 3:00:00 AM7/25/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...

>
> All those being sceptical about 1001% reliance on computer
> simulation of circuitswere right....
>
> I just tried it on the bench and it looks as though a zener
> diode does have a negative-resistance region(s) at low
> currents.
>
> 1. 0.5uA (yes 1/2uA!) oscillation started, 60mV pk-pk, -ve
> switch followed by ramp upwards. Classic relaxation
> oscillator picture... volts increase to a region of
> neg-R, sudden discharge, ramps back up to the neg-R region
> again.
>
> 2. 80uA, same shape, 100mV pk-pk approx.

Tony, veeeerrrry interesting! Could you detail for us the part
you were using? Do any other similar parts show this relaxation
oscillation effect?

--
Winfield Hill hi...@rowland.org _/_/_/ _/_/_/_/
The Rowland Institute for Science _/ _/ _/_/ _/
Cambridge, MA USA 02142-1297 _/_/_/_/ _/ _/ _/_/_/
_/ _/ _/ _/ _/
http://www.artofelectronics.com/ _/ _/ _/_/ _/_/_/_/


Winfield Hill

unread,
Jul 25, 1997, 3:00:00 AM7/25/97
to

Mike, <NoS...@Today.Thanks> said...

>
> It is highly unlikely that the possibility of oscillating zeners
> would have gone unnoticed by the semiconductors engineers and
> scientists, but be noticed by a few individuals on a newsgroup.
> [snip]

>
> It is not described in The Art of Electronics.
> [snip]

Mike, I'm sorry, but that can mean 1) we couldn't expend valuable
space, or 2) Paul and I were unaware of such a thing.

In this case it's choice 2). But I do intend to find out. I'm a big
beleiver in the real world of the bench rather than just the world of
theory and literature - although I usually find after painfully
exploration, details can be found in the [sometimes obscure] printed
record. After spending days modelling and at the bench, I'm very
motivated to find and read an obscure research paper or thesis, which
seemed uninteresting before.

Tony Williams' <to...@ledelec.demon.co.uk> posting is interesting.
"0.5uA oscillation started, 60mV pk-pk, ... Classic relaxation
oscillator picture... 80uA, same shape, 100mV pk-pk approx."

As some know, I've been exploring avalanche mechanisms at very high
currents. Thanks, Tony, Looks like exploring small currents will be
interesting too.

Incidentally, Mike could you identify yourself to us? Full name and
affiliation, etc. Student affiliations are excellent too. And maybe
even a decodeable email address? No spam intended.

Tony Williams

unread,
Jul 25, 1997, 3:00:00 AM7/25/97
to

In article <5r8rpm$e...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:

> Tony, veeeerrrry interesting! Could you detail for us the part
> you were using? Do any other similar parts show this relaxation
> oscillation effect?

Ok, more results below:-

First I repeat the caution re the picture being reported. I am
doing this with an ordinary scope, ie non-storage. There is lots
of timing-jitter and it's virtually impossible to lock. I am
reporting what I think are reasonable approximations.

Zeners that do oscillate, from my bits box.

BZX79C10, BZX85C12, Mot400mW 8V2 and 10V, BZX79 12V, BZX79C11.

Zeners that don't oscillate.

BZX793V9, BZY886V2, BZX794V7, BZY885V1.

Observations.

1. The dividing line is 6v2 and someone has already mentioned
the difference between Zener action and avalanching.

2. There appears to be 3/4 modes of oscillation:-

2a Mode.1, you are looking at residual 50Hz and increasing
voltage slowly. Suddenly odd little spikes appear, single
avalanches triggering at random. The Mot400mW 8v2 started
up at 12nA, the BZX79C10 at 500nA, the rest in between.

2b Mode.2, a classic relaxation osc, -ve discharge, R-C charge
back up again. Amplitude about 50/60mV pk-pk, increasing
slightly with increased current, but *not* linearly.
Frequency very jittery and increasing with current.

2c Mode.3, at the top end of Mode.2 "flats" in the waveform
appear, first on the bottom and then also on the top. The
waveform has shifted to being squarish. A new timing mech
seems to be coming in that allows it to dwell at fixed-v
for a few 100nS or so. Think maybe die-temperature?

2d Mode.4, The squareish waveform changes to spikes of larger
amplitude and this shape remains, but decreasing with
increasing current until oscillation stops. Zeners <10v
stopped at <160uA, Zeners >11v were still going at 1mA.
---------------------------------------------------------------

Extras.

3. I held a soldering iron onto the lead of a C10. In all modes
the picture shifted, but when I also brought the current
back to what it had been at ambient the correct picture
returned.

4. If you shine a strong light onto any zener the oscillation
always reduces in amplitude, being most sensitive in the
lower Modes. The current change with light was 1uA approx.

5. I put a 4700pF across the original C10 in order to swamp
circuit strays and give a less fuzzy picture. Results:-

Iin= 1uA,.... 5-15mV pk-pk for the triangle.

Iin= 5-50uA, 25-30mV pk-pk for the triangle.

Iin> 100uA, Mode.3, too fuzzy.

(Note the difference in amplitude previously reported in 2b,
ie without a big shunt-C. From what I can see the 4700pF
perhaps also stopped the whole waveform from jumping up
and down.)

Because of the jitter I will not report any timings, merely
note that we are in the 100nS to 1uS region.

Tony Williams

unread,
Jul 25, 1997, 3:00:00 AM7/25/97
to

In article <ant25090...@ledelec.demon.co.uk>, Tony Williams
<URL:mailto:to...@ledelec.demon.co.uk> wrote:

> 5. I put a 4700pF across the original C10 in order to swamp
> circuit strays and give a less fuzzy picture. Results:-
>
> Iin= 1uA,.... 5-15mV pk-pk for the triangle.
>
> Iin= 5-50uA, 25-30mV pk-pk for the triangle.
>
> Iin> 100uA, Mode.3, too fuzzy.
>
> (Note the difference in amplitude previously reported in 2b,
> ie without a big shunt-C. From what I can see the 4700pF
> perhaps also stopped the whole waveform from jumping up
> and down.)
>
> Because of the jitter I will not report any timings, merely
> note that we are in the 100nS to 1uS region.
>

I'm replying to my own post here, but have some extra results.

The 22k source-R I used bothered me slightly, so I knocked up
a simple 1 to 50uA current source, npn transistor, etc, 4700pF
still in there. For the same BZX79C10 above I got the following:-

Iin= 1uA ... 10-30mV triangles, and to make it clear these are
triangles of varying size, almost as though there
are different "avalanche-diodes" firing.

Iin= 50uA... 90mV pk-pk triangles on average, say about 10mV
variation in amplitude.

Charge Time is linear, about 8uS for 90mV at 50uA.
That sum says 4444pF, not bad.

Discharge is an RC-shape, about 2-3uS, which gives
about 500R for the avalanche resistance.

Note that these later results differed from 5 above by quite
a significant amount. I pondered on this and the answer was
staring me in the face.... as I was looking at it, the sun came
from behind a cloud, shone onto the test setup and the pk-pk mV
dropped down. This photosensitivity of the avalanching is
quite intriguing, it would appear that the larger avalanche
swings are the ones that get knocked out by light.

Patrick Lawler

unread,
Jul 27, 1997, 3:00:00 AM7/27/97
to

On Thu, 24 Jul 1997 15:45:07 +0100 (BST), Tony Williams
<to...@ledelec.demon.co.uk> wrote:

> All those being sceptical about 1001% reliance on computer
> simulation of circuits were right....

There's nothing wrong with computer simulations. All you have to do
is specify _all_ the characteristics of your circuit. Even the
undocumented characteristics. ;)

> I just tried it on the bench and it looks as though a zener
> diode does have a negative-resistance region(s) at low
> currents.

<snip>

I remember diodes being used for broadband noise generators &
oscillators years ago. The tunnel diode comes to mind.
It doesn't surprise me that other diodes have similar modes of
operation.

Were you able to get an idea of the oscillation frequency (order of
magnitude)?

Patrick Lawler
pla...@west.net

Tony Williams

unread,
Jul 27, 1997, 3:00:00 AM7/27/97
to

In article <33dc5c8b...@news.west.net>, Patrick Lawler

<URL:mailto:pla...@west.net> wrote:
>
> On Thu, 24 Jul 1997 15:45:07 +0100 (BST), Tony Williams
[snip]

> I remember diodes being used for broadband noise generators &
> oscillators years ago. The tunnel diode comes to mind.
> It doesn't surprise me that other diodes have similar modes of
> operation.
>
> Were you able to get an idea of the oscillation frequency (order of
> magnitude)?

Perhaps someone who knows semiconductor physics could answer
this better, and I'm sure that this effect must already be
documented somewhere. This is the best I can do:-

The mechanism involved would seem to be many "microavalanche"
diodes in parallel, all at slightly different triggering-V
and all able to conduct briefly at random. The voltage between
On and Off varies from 10mV and 100mV approximately. Each of
these avalanches produces a negative edge from a source-R of
about 500ohms. That negative edge hits the external circuitry
and the type of oscillation that results then depends on the
source-R, L and C. So there is no answer to your question,
except to say that Freq is very jittery. With an external
4700pF I was able to force it into a relaxation oscillator mode.

There would also seem to be a second mode of oscillation where
the "microavalanche" diodes also get discretely shifted, maybe
by their own local temperature change as they absorb the spikes
of energy. This happens at slightly higher currents and would
appear to have more energy available to cause troubles with.

I have now tested every device I have in stock (118) and all
zeners 8v2 and up do oscillate, 6v2 and below do not. I do not
possess any 5v6, 6v8, or 7v5 devices. Semiconductor surge
suppressors have also been tested and have exactly the same
oscillation.

Note: Some Motorola zeners, circa 1980, were notable for having
a small oscillation band of current. I got a sense that maybe
this could be attributed to their better quality. But this is
only a guess.

A general warning..... It would be wise to assume that 12v Zeners
and above are still oscillating at 1mA and it would seem very
advisable to run such devices at not less than 3mA. Any analogue
circuit that was powered from an oscillating zener would be
difficult to tame and may even show dc instabilities.

As John Woodgate has already pointed out in this thread, the
avalanche type of oscillation is not easy to get rid of,
adding a few 1000pF of shunt-C merely reduces it's frequency.
0.1uF, or greater, would seem prudent across any zener.

Winfield Hill

unread,
Jul 27, 1997, 3:00:00 AM7/27/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...
>
> Patrick Lawler <pla...@west.net> wrote:
>>
>> I remember diodes being used for broadband noise generators ...

>
> The mechanism involved would seem to be many "microavalanche"
> diodes in parallel, all at slightly different triggering-V
> and all able to conduct briefly at random. The voltage between
> On and Off varies from 10mV and 100mV approximately. Each of
> these avalanches produces a negative edge from a source-R of
> about 500ohms. That negative edge hits the external circuitry
> and the type of oscillation that results then depends on the
> source-R, L and C. So there is no answer to your question,
> except to say that Freq is very jittery. With an external
> 4700pF I was able to force it into a relaxation oscillator mode.

Now we have to also question the common use of a zener as a noise
source! Maybe unselected zeners aren't very high-quality noise
sources after all! What are you doin' here Tony anway? Are you
sure there isn't something wierd about your test setup?

Like a poor grounding system, etc.? Some kind of hysteresis?

Tony Williams

unread,
Jul 27, 1997, 3:00:00 AM7/27/97
to

In article <5rg9be$a...@news-central.tiac.net>, Winfield Hill

<URL:mailto:hi...@rowland.org> wrote:
>
> Tony Williams, <to...@ledelec.demon.co.uk> said...
> >
> > Patrick Lawler <pla...@west.net> wrote:
> >>
> >> I remember diodes being used for broadband noise generators ...
> >
> > The mechanism involved would seem to be many "microavalanche"
> > diodes in parallel, all at slightly different triggering-V
> > and all able to conduct briefly at random. The voltage between
> > On and Off varies from 10mV and 100mV approximately. Each of
> > these avalanches produces a negative edge from a source-R of
> > about 500ohms. That negative edge hits the external circuitry
> > and the type of oscillation that results then depends on the
> > source-R, L and C. So there is no answer to your question,
> > except to say that Freq is very jittery. With an external
> > 4700pF I was able to force it into a relaxation oscillator mode.
>
> Now we have to also question the common use of a zener as a noise
> source! Maybe unselected zeners aren't very high-quality noise
> sources after all! What are you doin' here Tony anway? Are you
> sure there isn't something wierd about your test setup?
>
> Like a poor grounding system, etc.? Some kind of hysteresis?


Hmm... When doubted by the likes of WH I go back and check it.

I went back to the simplest circuit, a 28v variable supply,
22k series-R, into the zener. Scope across the zener. DVM
ammeter removed just in case of spillback from it.

Sorry chum, turn the volts up slowly and that ordinary 400mW
zener, C10, goes off like a rocket, exactly as before.

That's two different setups I've used, even different power
supplies, both linear, and I have even checked for no noise
from the supply when the zener is oscillating. Come to think
of it, to check the 1.5KE39A surge suppressors I used yet
another supply and test setup.

The nutcruncher for me is that shining a torch onto the zener
causes the osc to drastically reduce. No earth loops in a torch.

Re "use of a zener as a noise source". If you do not have the
4700pf in there and you turn the timebase on the scope back
down, the picture looks exactly like grassy random noise.
That's because of all those "microavalanche" diodes firing away
at random, working against stray and diode capacitance, and so
producing random-sized triangles (or squares at higher-I).

Win, you blighter, you've just stuck me out on a limb. Well,
until you prove otherwise I'm sticking to my guns.

Come on, let someone else fire up that simple circuit and have
a look for themselves. Don't forget, 8v2 or upwards.

Paul M. Jaeger

unread,
Jul 27, 1997, 3:00:00 AM7/27/97
to

Winfield Hill wrote:
>
> Tony Williams, <to...@ledelec.demon.co.uk> said...
> >
> > Patrick Lawler <pla...@west.net> wrote:
> >>
> >> I remember diodes being used for broadband noise generators ...
> >
> > The mechanism involved would seem to be many "microavalanche"
> > diodes in parallel, all at slightly different triggering-V
> > and all able to conduct briefly at random. The voltage between
> > On and Off varies from 10mV and 100mV approximately. Each of
> > these avalanches produces a negative edge from a source-R of
> > about 500ohms. That negative edge hits the external circuitry
> > and the type of oscillation that results then depends on the
> > source-R, L and C. So there is no answer to your question,
> > except to say that Freq is very jittery. With an external
> > 4700pF I was able to force it into a relaxation oscillator mode.
>
> Now we have to also question the common use of a zener as a noise
> source! Maybe unselected zeners aren't very high-quality noise
> sources after all! What are you doin' here Tony anway? Are you
> sure there isn't something wierd about your test setup?
>
I purchased some noise diodes (from MDF products I think) a few years
ago for an application in the 1-20MHz range. I found that they were
very sensitive to the bias current. At 250uA they made nice Gaussian
grass, at higher or lower currents the noise became quite spikey.

Paul Jaeger
Guided Therapy Systems, Inc.
Mesa, AZ

slo...@sci.kun.nl

unread,
Jul 28, 1997, 3:00:00 AM7/28/97
to Tony Williams

In article <ant24140...@ledelec.demon.co.uk>,

Tony Williams <to...@ledelec.demon.co.uk> wrote:
>
> In article <8694870...@dejanews.com>, <URL:mailto:slo...@sci.kun.nl>
> wrote:
>
> [big snip, Bill being sceptical about Spice]
>
> > But, I - for one - retain enough of my sceptical faculties to be
> > unconvinced that a mastery of Spice is the be-all and end-all of the
> > electronics, which the proposition that Mike<NoS...@Today.Thanks> was
> > touting in this thread.
>
> All those being sceptical about 1001% reliance on computer
> simulation of circuitswere right....
>
> I just tried it on the bench and it looks as though a zener
> diode does have a negative-resistance region(s) at low
> currents.
>
> Setup:- Variable supply, 0-28v, uAmmeter, 22k, zener. Scope
> across the zener (79C10).
>
> Results:- Caution, the oscillations were difficult to lock
> for any length of time, so I had to snatch approx
> view and measurements.
>
> 1. 0.5uA (yes 1/2uA!) oscillation started, 60mV pk-pk, -ve
> switch followed by ramp upwards. Classic relaxation
> oscillator picture... volts increase to a region of
> neg-R, sudden discharge, ramps back up to the neg-R region
> again.
>
> 2. 80uA, same shape, 100mV pk-pk approx.
>
> 3. 100uA, difficult to see, but flat sections top and bottom,
> >100mV pk-pk, going squarish maybe.
>
> 4. 160/170uA oscillation getting intermittant/disappearing.
>
> 5. >170uA no oscillation.
>

Really nice to see some experimental evidence. I sit here wondering why
I didn't bother doing it for myself .... don't bother mentioning the words
"lazy bastard".

If I had, of course, I would have known why you couldn't put a number on
the frequency.

But anyway, congratulations on putting the *science* back into
sci.electronics.design.

Jeroen Belleman

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

In article <8700991...@dejanews.com>, <slo...@sci.kun.nl> wrote:
>In article <ant24140...@ledelec.demon.co.uk>,
> Tony Williams <to...@ledelec.demon.co.uk> wrote:
>> I just tried it on the bench and it looks as though a zener
>> diode does have a negative-resistance region(s) at low
>> currents.
>
>Really nice to see some experimental evidence.

Here's some more:

I used a BZX55C10 diode, at 45uA, with a 22k bias resistor. In the
time domain, the behaviour fits Tony's description. The voltage at
which avalanche sets in is more or less randomly (but not uniformly)
distributed in a 100mV range around 10V-and-some.

The signal's spectrum is typical for that of noise. It's flat up to
about 10 MHz and then drops at an odd 9 dB per octave. I'd like to
see someone explain *that* convincingly.

I'd hazard a guess and say that this whole thing can be explained
by considering the energy distribution of charge carriers in the
junction region. I'd be somewhat out on a limb if someone asked me
to actually do it.

In conclusion, the diode doesn't really oscillate, but it does
generate lots of noise. That's no surprise after all.


--

Jeroen Belleman
Jeroen....@cern.ch

Walter Gray

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

In article <5rg9be$a...@news-central.tiac.net>, hi...@rowland.org (Winfield Hill) writes:
>Tony Williams, <to...@ledelec.demon.co.uk> said...
>>
>> Patrick Lawler <pla...@west.net> wrote:
>>>
>>> I remember diodes being used for broadband noise generators ...
>>
>> The mechanism involved would seem to be many "microavalanche"
>> diodes in parallel, all at slightly different triggering-V
>> and all able to conduct briefly at random. The voltage between
>> On and Off varies from 10mV and 100mV approximately. Each of
>> these avalanches produces a negative edge from a source-R of
>> about 500ohms. That negative edge hits the external circuitry
>> and the type of oscillation that results then depends on the
>> source-R, L and C. So there is no answer to your question,
>> except to say that Freq is very jittery. With an external
>> 4700pF I was able to force it into a relaxation oscillator mode.
>
> Now we have to also question the common use of a zener as a noise
> source! Maybe unselected zeners aren't very high-quality noise
> sources after all! What are you doin' here Tony anway? Are you
> sure there isn't something wierd about your test setup?
>
> Like a poor grounding system, etc.? Some kind of hysteresis?
>


The irregularity made me wonder if Tony was seeing random
ionisation events caused by background radiation. The pulse
shape would be controlled by the external components. It might
be worth screening the zener with a bit of lead sheet.

Walter


Winfield Hill

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

Walter Gray, <wag...@taz.dra.hmg.gb> said...

>
> The irregularity made me wonder if Tony was seeing random
> ionisation events caused by background radiation. The pulse
> shape would be controlled by the external components. It might
> be worth screening the zener with a bit of lead sheet.

Nice idea. Worth a try.

However. the cosmic-ray flux is certainly too low for the high
occurence rate Tony reports, especially considering the small
diode-junction volume.

Tony Williams

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

In article <EE2o4...@news.cern.ch>, Jeroen Belleman

<URL:mailto:jer...@sp056.cern.ch> wrote:
>
> In article <8700991...@dejanews.com>, <slo...@sci.kun.nl> wrote:
> >In article <ant24140...@ledelec.demon.co.uk>,
> > Tony Williams <to...@ledelec.demon.co.uk> wrote:
> >> I just tried it on the bench and it looks as though a zener
> >> diode does have a negative-resistance region(s) at low
> >> currents.
> >
> >Really nice to see some experimental evidence.
>
> Here's some more:
>
> I used a BZX55C10 diode, at 45uA, with a 22k bias resistor. In the
> time domain, the behaviour fits Tony's description. The voltage at
> which avalanche sets in is more or less randomly (but not uniformly)
> distributed in a 100mV range around 10V-and-some.

Thanks for the confirmation.



> The signal's spectrum is typical for that of noise. It's flat up to
> about 10 MHz and then drops at an odd 9 dB per octave. I'd like to
> see someone explain *that* convincingly.
>
> I'd hazard a guess and say that this whole thing can be explained
> by considering the energy distribution of charge carriers in the
> junction region. I'd be somewhat out on a limb if someone asked me
> to actually do it.

I discovered a previous post by Mark Zenier referring to a
Motorola document. The document used the words "microplasma
discharge". Alta Vista only produced one reference against
those keywords, not much use.


> In conclusion, the diode doesn't really oscillate, but it does
> generate lots of noise. That's no surprise after all.

The use of the word oscillation is certainly a moot point.

Each little negative avalanche-edge shock-excites any LC that
may be there and the waveshapes shapes produced are defined by
the source-R, L, and C. However, the random amplitude of the
edges being generated does result in a signal that is random,
both in size and frequency, so that presumably leans it towards
the term noise generator.

Tony Williams

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

In article <5rklpp$f7j$5...@trog.dra.hmg.gb>, Walter Gray
<URL:mailto:wag...@taz.dra.hmg.gb> wrote:

[snip]

> The irregularity made me wonder if Tony was seeing random
> ionisation events caused by background radiation. The pulse
> shape would be controlled by the external components. It might
> be worth screening the zener with a bit of lead sheet.

I have the damned thing running permanently on the corner of
the bench, so that..... No lead to hand, but I put some tape
on the diode and wound on two layers 22-gauge solder. No diff.

The neg-edges are *very* sensitive to light though. Flooding
it with a torch gives the same effect as reducing the current.

slo...@sci.kun.nl

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to Jeroen Belleman

In article <EE2o4...@news.cern.ch>,

jer...@sp056.cern.ch (Jeroen Belleman) wrote:
>
> In article <8700991...@dejanews.com>, <slo...@sci.kun.nl> wrote:
> >In article <ant24140...@ledelec.demon.co.uk>,
> > Tony Williams <to...@ledelec.demon.co.uk> wrote:
> >> I just tried it on the bench and it looks as though a zener
> >> diode does have a negative-resistance region(s) at low
> >> currents.
> >
> >Really nice to see some experimental evidence.
>
> Here's some more:
>
> I used a BZX55C10 diode, at 45uA, with a 22k bias resistor. In the
> time domain, the behaviour fits Tony's description. The voltage at
> which avalanche sets in is more or less randomly (but not uniformly)
> distributed in a 100mV range around 10V-and-some.
>
> The signal's spectrum is typical for that of noise. It's flat up to
> about 10 MHz and then drops at an odd 9 dB per octave. I'd like to
> see someone explain *that* convincingly.

The Fourier transform of a Dirac spike is flat from the repetition rate
of the spike to the width of the spike. Within that range, the spectrum
is going to look like white noise. Neither you nor Tony mentions the
repetition rate you see with a 'scope. For 45uA charging 90pF through
100mV,you'd get a repetition rate of 5MHz - since the 90pF is with zero
volts across the zener, this is a lower limit. I'd suspect that the
voltage swing within the diode is bigger, and the repetition rate lower.

In the literature on SPADs - single photon avalanche photodiodes - the
point is made that a certain minimum current is required to sustain an
avalanche near threshold. At threshold, each charge carrier crossing the
junction has to generate - on average - one more charge carrier, but this
is a random function and if you reduce the current until there is only
one charge carrier in the junction at any one time, it is clear that the
random fluctuations in avalanche yield will extinguish the avalanche
within a few transit times, and you have to wait until thermal
fluctuation generates another charge carrier before the avalanche can
resume.

In the meantime, the junction capacitance will charge up to some higher
voltage, so that the avalanche, when it resumes, will generate an excess
of charge carriers.

So we end up with a relaxation oscillator, with a fairly erratic interval
between avalanches, which blurs out the nice rectangular Fourier
transform of the classic Dirac spike.

> I'd hazard a guess and say that this whole thing can be explained
> by considering the energy distribution of charge carriers in the
> junction region. I'd be somewhat out on a limb if someone asked me
> to actually do it.

The fact that one can concoct an explanation without reference to the
energy distribution of the charge carriers in the junction region doesn't
mean that it isn't important. I'd be interested to learn whether an
"avalanche" zener diode (ie one with a breakdown voltage over about 6V)
had a significant junction transit time, since the IMPATT diode relies on
operating at an electric field over 10^4 V/m where the carrier velocity
in silicon is saturated, but this is just idle speculation.

>
> In conclusion, the diode doesn't really oscillate, but it does
> generate lots of noise. That's no surprise after all.

One might equally conclude that the diode was *really* acting as a
relaxation oscillator with a rather erratic inter-pulse interval. The
right LC tank circuit might act to stabilise the interval. My informants
in 1973 talked of oscillation at around 200MHz.

In fact, the shot noise on an avalanche should be perfectly predictable -
it is just the square root of the number of charge carriers - and our
"oscillating" zeners should be worse.

Ought to be a publication in there somewhere.

John Woodgate

unread,
Jul 29, 1997, 3:00:00 AM7/29/97
to

In article <EE2o4...@news.cern.ch>, Jeroen Belleman
<jer...@sp056.cern.ch> writes

>In conclusion, the diode doesn't really oscillate, but it does
>generate lots of noise. That's no surprise after all.
>

I was afraid that this would happen. Real oscillations are possible but
do not always occur: the noise is a very well-known but entirely
separate characteristic of avalanche (Zeners > 6.8 V) diodes, which
always occurs, at normal operating currents as well as at very low
currents.

Winfield Hill

unread,
Jul 30, 1997, 3:00:00 AM7/30/97
to

slo...@sci.kun.nl, <slo...@sci.kun.nl> said...

>
> In fact, the shot noise on an avalanche should be perfectly predictable
> - it is just the square root of the number of charge carriers - and our
> "oscillating" zeners should be worse.

Well, hmmm, not the usual number-of-carriers = current / electron-charge,
but rather the number-of-avalanche-events = current / electron-charge *
avalanche-multiplication. Let's see. Here's an really off-the-wall
back-of-the-envelope ad-hoc order-of-magnitude estimated calculation:

A current of say 20uA is 2E-5/1.6E-19*1E9 = 125,000 electrons / ns.
If the multiplication is say x 125, that's a thousand avalanche events
per ns. If the "average" duration of an avalanche is 25ns, then we get
25,000 avalanche events at once and about SQRT 25,000 = 158 / 25000 =
0.6% rms current variation.

Now. let's see, ahhh mmm, 0.6% of 20uA = 126nA times the zener
"impedance" ahhh err 3500 ohms at 20uA = 440uV noise, ahh rms, ahhh,
crest factor, ahh errr gulp x 3.5 = 1.5mV peak ahh x2 = 7mV pk-pk...

Let's see, Tony Williams <to...@ledelec.demon.co.uk> said "0.5uA
oscillation started, 60mV pk-pk, ... 80uA, same shape, 100mV pk-pk
approx." Of course, he had a big capacitor across the zener, which
average out the avalanches in the above "calculation" and reduce the
noise, ah hmmm.... OK gang, over to you.

Bill Sloman

unread,
Jul 30, 1997, 3:00:00 AM7/30/97
to Tony Williams, Mark Zenier

In article <5rko79$m...@news-central.tiac.net>, hi...@rowland.org (Winfield Hill) says:
>
>Walter Gray, <wag...@taz.dra.hmg.gb> said...

>>
>> The irregularity made me wonder if Tony was seeing random
>> ionisation events caused by background radiation. The pulse
>> shape would be controlled by the external components. It might
>> be worth screening the zener with a bit of lead sheet.
>
> Nice idea. Worth a try.
>
> However. the cosmic-ray flux is certainly too low for the high
> occurence rate Tony reports, especially considering the small
> diode-junction volume.

Quite apart from the fact that the BZX79C10 has a reverse current of
200nA at 7V, which presumably represents the thermally generated current
carriers, un amplified by avalanche multiplication.

This represents a much higher occurence rate than Tony reports - I
calculated something like 5pA - and I reluctantly agree to the
necessity to invoke the multiple avalanche sites mentioned in Mark
Zenier's post form the 1980 Motorola Zener Diode Manual


" Between the minimum current shown in Figure 4-4 and the leakage

currents, there is the "knee" region. The avalanche mechanism may not


occur simultaneously across the entire area of the P-N junction, but first
at one microscopic site, then at an increasing number of sites as further
voltage is applied. This action can be accounted for by the "microplasma
discharge theory" and correlates with several breakdown characteristics"

Each of say 40,000 avalanche sites has then has its own 5pA worth
of thermally generated current carriers, and Tony is looking at the
one with the lowest avalanche voltage - raise the current to 170uA,
and this one saturates - probably gets hot enough to increase its
avalance voltage to match the next lowest, though I guess a space charge
mechanism could also work.

With 40,000 sites, a 90mV gap between the first two seems rather large,
but the breakdown behavior of the diode will be dominated by the sites
with the lowest avalanche voltages, so we can probably place the centre
of the breakdown voltage distribution way higher than 10V.

Presumably Tony's less successful diodes would have had more closely
spaced "lowest avalanche voltages".


Bill Sloman (slo...@sci.kun.nl) | Precision analog design
TZ/Electronics, Science Faculty, | Fast analog design and layout
Nijmegen University, The Netherlands | Very fast digital design/layout
| e-mail for rates and conditions.

Dave VanHorn

unread,
Jul 31, 1997, 3:00:00 AM7/31/97
to

I've been wondering about this one in my copious spare time :)

Could it be that the avalanche events trigger nearby sites to
avalanche as well? I'm not sure what the coupling mechanism
would be here..

If you have a zener on the end of any kind of leads, then you
have L in circuit, and if the avalanche behaves in that manner,
then you could deplete the local charge at the junction faster
than the incoming current can fill it due to the series L.

I would expect this to be an effect that would only be observable
at very low currents, and it may be process dependent too.

Dave VanHorn

unread,
Jul 31, 1997, 3:00:00 AM7/31/97
to

Bill Sloman

unread,
Aug 1, 1997, 3:00:00 AM8/1/97
to

In article <N7XvQYAf...@jmwa.demon.co.uk>, John Woodgate <j...@jmwa.demon.co.uk> says:
>
>In article <EE2o4...@news.cern.ch>, Jeroen Belleman
><jer...@sp056.cern.ch> writes
>>In conclusion, the diode doesn't really oscillate, but it does
>>generate lots of noise. That's no surprise after all.
>>
>
>I was afraid that this would happen. Real oscillations are possible but
>do not always occur: the noise is a very well-known but entirely
>separate characteristic of avalanche (Zeners > 6.8 V) diodes, which
>always occurs, at normal operating currents as well as at very low
>currents.

I wonder what a "real" oscillation is? Is it a repetitive fluctuation?
Both Tony Williams and Jeroen Belleman are seeing that.

Jeroen Belleman seems to deny that this is an oscillation because the
fluctuations differ markedly from one interval to the next. He may
be right. Nobody talks about the human heart as an oscillator, and in
fact it's pattern of repetition is chaotic.

I think that is extremely likely that noise on avalanche zeners (Sze
asserts that tunnelling effects are significant in zeners up to 8V)
is very closely related to the erratic avalanching we have been
discussing.

Despite Winfield Hill's opinion on the subject, a stable avalanche process
giving a stable current has an avalanche gain of one - each charge
carrier on average generates one new charge carrier, and the noise is
only higher than the square root of the number of charge carriers in
the proportion that the distribution of avalanche gain above and below
one over-represents the high gain carriers.

This effect is discussed in the photomultiplier literature, and is pretty
small.

What we appear to have in zener diodes is an unstable avalanche process,
where the charge carrier that starts a new avalanche is dramatically
over-represented, giving rise to lots of excess noise.
These unstable avalanches appear to be susceptible to entraining by
even a meduim Q resonator - Tony Williams 100nF capacitor for instance
- to produce something that even Jeroene Belleman would recognise as
a *real* oscillation.

Tony Williams

unread,
Aug 1, 1997, 3:00:00 AM8/1/97
to

In article <5rsm58$5n5$1...@wnnews.sci.kun.nl>, Bill Sloman

<URL:mailto:slo...@sci.kun.nl> wrote:
>
> In article <N7XvQYAf...@jmwa.demon.co.uk>, John Woodgate <j...@jmwa.demon.co.uk> s
> ays:
> >
> >In article <EE2o4...@news.cern.ch>, Jeroen Belleman
> ><jer...@sp056.cern.ch> writes
> >>In conclusion, the diode doesn't really oscillate, but it does
> >>generate lots of noise. That's no surprise after all.
> >>
> >
> >I was afraid that this would happen. Real oscillations are possible but
> >do not always occur: the noise is a very well-known but entirely
> >separate characteristic of avalanche (Zeners > 6.8 V) diodes, which
> >always occurs, at normal operating currents as well as at very low
> >currents.
>
> I wonder what a "real" oscillation is? Is it a repetitive fluctuation?
> Both Tony Williams and Jeroen Belleman are seeing that.
>
> Jeroen Belleman seems to deny that this is an oscillation because the
> fluctuations differ markedly from one interval to the next. He may
> be right. Nobody talks about the human heart as an oscillator, and in
> fact it's pattern of repetition is chaotic.

I agree with Jeroen in the use of the word "noise" to describe this
output from a biassed zener. The reason for that is that the source
of what we see on the scope are randomly-sized negative impulses
from what I called "microavalanches" in the zener.

Certainly you can connect external components and force certain
recognisable shapes onto the output (Triangles/Sines) but all
such shapes are still really only derived from kicking RLC
circuits with random-sized edges and the random nature of the
shapes thus created merely reflect the randomness of the source
of the energy.

I should note though that the word "noise" does have an achilles
heel.... the output impulses are always in one direction, negative,
and are always a relative sharp edge... the external circuitry
determines the shape of the climb back up and therefore does play
a part in determing the average and pk-pk rep-rate of the "noise".

So maybe we should agree to differ and just argue on the ratios.
My vote says 80:20, 80% Noise versus 20% Oscillation.



>
> I think that is extremely likely that noise on avalanche zeners (Sze
> asserts that tunnelling effects are significant in zeners up to 8V)
> is very closely related to the erratic avalanching we have been
> discussing.
>
> Despite Winfield Hill's opinion on the subject, a stable avalanche process
> giving a stable current has an avalanche gain of one - each charge
> carrier on average generates one new charge carrier, and the noise is
> only higher than the square root of the number of charge carriers in
> the proportion that the distribution of avalanche gain above and below
> one over-represents the high gain carriers.
>
> This effect is discussed in the photomultiplier literature, and is pretty
> small.
>

My gut feeling also says avalanche, but semiconductor physics
is not my field.

Tony Williams

unread,
Aug 1, 1997, 3:00:00 AM8/1/97
to

I sliced into the back half of Bill's last post to address this
particular point.

In article <5rsm58$5n5$1...@wnnews.sci.kun.nl>, Bill Sloman
<URL:mailto:slo...@sci.kun.nl> wrote:

> These unstable avalanches appear to be susceptible to entraining by
> even a meduim Q resonator - Tony Williams 100nF capacitor for instance
> - to produce something that even Jeroene Belleman would recognise as
> a *real* oscillation.

Bill's been going on about the possibility of "entraining", on
and off for the last week. Because he's so bone idle I have had
to give in and try resonant circuits around this biassed C10.

Here are the results:-

I wound 100 turns onto a gapped RM core that was handy, the
exact type is not known, but it has "400" on it, so I guess
100T gives 4mH.

4mH/4700pf resonates at about 36.7 KHz, 27uS.

1. Series-resonant circuit in parallel with the zener, 22k
feed resistor, Cap being the lower element, with the scope
across it to look at the resonant current.

Result. Off it went, sinewave, good shape on top, tending
to have a point on the bottom, about 300mV pk-pk. Period
varied slightly with stimulus-I, 20-25uS. Very jittery.

2. Parallel-resonant circuit, LC between zener and 0V, 22k
shorted out. Scope across the LC.

Result. Not a bad sinewave, about 50mV pk-pk, 20uS, Freq
not affected by stimulus-V. Very jittery.

So, Bill was right... sort of. A resonant circuit *will* shape
the negative impulses into some sort of sine and that sine will
modulate the stimulus on the zener so that it tends to be forced
to firing points in sync. However, the zener still wins because
there is still enough randomness, even in the "synced" firing
points as to make the waveform too jittery to be useable.

nick toop

unread,
Aug 1, 1997, 3:00:00 AM8/1/97
to

In article <ant01154...@ledelec.demon.co.uk>, Tony Williams
<to...@ledelec.demon.co.uk> writes

Are you sure the resonant circuit is feeding back to the noise source?

I did a simple numeric simulation of noise into a fairly high Q RLC
circuit and you get quite nice sine waves but the envelope amplitude
varies, every now and then going to zero when a new phase is
established. I enclose a .GIF which I hope is small enough not to cause
offence..

[ Section: 1/1 File: ring.gif Encoder: Turnpike Version 3.03a ]

begin 644 ring.gif
<encoded_portion_removed>
end

sum -r/size 15911/5611 section (from "begin" to "end")
sum -r/size 58790/4052 entire input file

Regards,

--
nick toop

Winfield Hill

unread,
Aug 2, 1997, 3:00:00 AM8/2/97
to

Bill Sloman, <slo...@sci.kun.nl> said...

>
> Despite Winfield Hill's opinion on the subject, a stable avalanche
> process giving a stable current has an avalanche gain of one - each
> charge carrier on average generates one new charge carrier, and the
> noise is only higher than the square root of the number of charge
> carriers in the proportion that the distribution of avalanche gain
> above and below one over-represents the high gain carriers.
>
> This effect is discussed in the photomultiplier literature, and is
> pretty small.

A gain of 1 - hah! Some _avalanche_ process that would be. Bill,
really, a PMT with unity gain? OK, let's talk about a PMT.

The PMT is a good example of the severe effect of multiplicative gain
on noise calculations. Let's consider a typical PMT, the Hamamatsu
R1527, which has 9 stages and a gain of about 5 million at 1000 volts.
This is about 110 volts per stage, and means each accelerated electron
striking a dynode creates about 5.5 new electrons, which we see from
observing that 5.5^9 = 5E6. So we see the average secondary-emission
ratio is much greater than unity - it ranges from 4 to 6 for different
tube designs and varies some with voltage, by V^0.8 typ. Of course
(V^0.8)^9 = V^7.2, which isn't a small effect at all!

Now let's consider a small light flux, so we get about 500 electrons
per second from the photocathode (125 are dark-current volunteers, but
that's OK). We know the statistics of a 500-electrons/sec average
flux will show about (sqrt 500) / 500 = 1/22 = 5% rms fluctuation.
And we know that each of these 500 electrons will produce short 20ns
pulses of about 5E6 electrons at the anode and that we'll therefore
get an average current of about 2.5E9 electrons or 0.4nA from the PMT.

By contrast, a typical 0.4nA current from a transistor or photodiode
will produce very different statistics: a shot-noise variation of
about 11.3fA rms with a 1Hz bandwidth, or about 0.003% (even less for
1-sec averaging). That's a pretty steady current, dramatically
different from our 0.4nA PMT output current with 5% rms noise.

The moral of the story: If when examining the output of a black box,
we observe a sizeable current with lots of variation, we might do well
to consider a high-gain multiplicative process originating with a
small number of events, like that of the PMT.

I'll have more to say about avalanche in a latter post.

Winfield Hill

unread,
Aug 2, 1997, 3:00:00 AM8/2/97
to

Bill Sloman, <slo...@sci.kun.nl> said...

>
> I think that is extremely likely that noise on avalanche zeners (Sze
> asserts that tunnelling effects are significant in zeners up to 8V)
> is very closely related to the erratic avalanching we have been
> discussing.
>
> Despite Winfield Hill's opinion on the subject, a stable avalanche
> process giving a stable current has an avalanche gain of one - each
> charge carrier on average generates one new charge carrier, ...

Some of a zener-diode's current is no doubt associated with low
avalanche gains, but I certainly haven't advanced any opinions about
that. In fact, my understanding is much higher gains than unity are
usually associated with avalanche processes. This is the argument put
forward in the old Motorola literature, complete with a nice drawing.

Let's review what Gandi says (I'll condense): Under the condition of
high electric fields, the velocity of individual carriers will exceed
their terminal drift velocity (10^7 cm/s and 6.5x10^6 cm/s for electrons
and holes in silicon) and become "hot" carriers. These have sufficient
energy in a collision to promote valence-band electrons to the
conduction band, creating a hole-electron pair. The impact ionization
effect is multiplicative, with newly-generated holes or electrons
involved in the ionization of further hole-electron pairs.

Most authorities, e.g. Thornton et.al. derive a multiplication factor,
M, e.g., with 1/M = 1 - (V/Vbr)^n where n = 1.5 to 6.5. We see that
M -> infinity as V -> the breakdown voltage, V_br. Some, e.g. Ghandi,
start with ionization coefficients for the number of hole-electron
pairs produced per-carrier per-cm traveled in the E-field, integrating,
etc., to develop separate M_n and M_p terms for the electron and hole
carriers, etc. entering a depletion layer. Even with different
exponents (4 and 6 resp), in the end they get similar results.

Few speculate in detail about the origination of carriers to start the
process, but all agree the factor M may be quite large, so one single
electron can generate quite a flood. In one noisy 15V zener, I have
measured typically 90 million electrons/event, and even up to nearly
500 million (more about that later). Do these events start with one
single carrier, perhaps at a surface defect? If so, the statistical
speculations I put forward, to which you object, Bill, are completely
appropriate.

BTW, as far as I can tell, Bill, no "unstable avalanche ... susceptible
to entraining by a medium Q resonator" is required.

Winfield Hill

unread,
Aug 2, 1997, 3:00:00 AM8/2/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...

>
> I agree with Jeroen in the use of the word "noise" to describe this
> output from a biassed zener. The reason for that is that the source
> of what we see on the scope are randomly-sized negative impulses
> from what I called "microavalanches" in the zener. [snip]
> [however] the output impulses are always in one direction, negative,

> and are always a relative sharp edge...

Below, the results of a few hours spent writing up a few minutes of
observation yesterday!

The first zener diode I chose showed an incredibly strong relaxation-
oscillation effect, just as Tony described. It was a Motorola 1N5245B
with manufacturing code 939. This is a 15V 5% 1/2W zener with a small
opaque-grey glass body. Interestingly, the next diode in the 1N5245B
drawer showed little or no effect, so I went back to the first one for
a detailed examination.

The amplitude of the spikes increased as I increased the current,
peaking around 50uA, where I took some more detailed measurements.

/| 1N5245B at 50uA
200mV FS / |
/| / | /|
/| / | /| / | /| / | /|
/ | /| / | / | / | /| / | / |/ | /| _____
| / |/ | /| / |/| / |/ | / |/ | / |/ |
|/ | / |/ |/|/ |/ | /|/ |
|/ |/ |
/
scope trace, continuous events, 10us FS 14.41 V
average value

Spike charge and energy. At low currents, say below 5uA, this diode
seemed happy enough in its (avalanche) discharge, but at higher
currents the spike events would start, but in a curious way.

The charge slope, which is 140mV/us, implies a circuit capacitance
(zener and cable) of about 314pF, but measuring this by adding a
1000pF 2% cap in parallel showed an actual effective value of 217pF
(much higher than Motorola's typical values). For example, at 50uA,
apparently a steady non-event current of about 20uA is always flowing
and attempts to force higher currents through the zener are ignored,
but for no more than a hundred nanoseconds, or so. First the ignored
30uA steadily charges the capacitance to a higher voltage. Then
suddenly some location inside the zener aggressively avalanches with
a discharge step ranging from -10 to -200mV, taking less than 10ns
(the limit of the scope I was using).

Electrons per event. We see that the discharge suddenly grabs up to
315pF * 205mV = 65pC from the capacitance, implying up to 6mA currents
and 400 million electrons in the event. The discharge events average
90 million electrons, and few are less than 1/2 that.

Spike period and statistics. The event-discharge time intervals are
quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
min/max). Observing with a 10us window, I _always_ count from 12 to
15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.
This is more like a relaxation oscillator with a noisy threshold and
a noisy discharge step, and less like a chaotic or random process.

Temperature. Hmmm, at 50uA the diode is dissipates about 0.75mW on
average, but the power during a 10ns step is about 90mW. Can this
miniscule 0.9nJ pulse of energy taken from the capacitance have any
effect? 500mW zeners are transient rated for 20W/1ms = 20mJ, which
presumably changes the junction temperature by say +150C. We can
adjust for our 10ns pulse: sqrt(10ns/1ms) * 20mJ => 60uJ/150C, and
obtain a +2.5 C/uJ temperature-rise for the whole junction at 10ns.

OK, sheer WAG speculation hat ON.
Let's assume a single localized event and estimate the thermal
spreading distance at say 20 microns in 10ns (check this later).
We guess that less than 0.5ppm of the junction area is available
to absorb energy during the event, leading to an instantaneous
micro-localized temperature rise of say +450C. This would increase
the number of intrinsic carriers available by 500x, exceeding the
doped level, and creating a "mesoplasma" current discharge.
Note that damaging mesoplasmas must be at much higher temperatures
(core well over 1000C) for a much longer time to do any damage.
Speculation hat OFF.

Higher currents. Upon increasing the current above 75uA, the "normal"
quiet diode avalanche process asserts itself more strongly and the
"voltage soar with negative-return spiking" occurs less often.

,| | |, | , ___+150mV
|||| ||: || |
|||| |, |||| ||:||
,._,.-,-_.,I||I,-.I|L|,_.-,_,._,.-||II,._,.-,-I||II|, __ 0mV

scope trace at 100uA, scattered events (5us/div)

Negative resistance. Curiously, the voltage is _reduced_ at higher
currents, as measured by an integrating DVM. This is because the
soar-with-spike-discharge bursts occur less frequently, slightly
reducing the average voltage. For example, my 1N5245 dropped about
40mV before resuming normal zener impedance properties.

continuous events (large)
volts continuous events /
14.41 - (small) __,..-=--,,.__ scattered events
14.40 - \ _,.-'~'`` `'-.,_ /
14.39 - _,-'` '-,_ rare events
14.38 - ,-'` '-,_ \
14.37 - / ``''===----
14.36 - | | | / | | |
20 uA 50 75 / 100 150 200
current -> /
/
"negative-resistance" region
Zener voltage goes down with increasing current.

I'm not inclined to make much of this "negative-resistance" region,
especially as a possible oscillator component, since it's just an
artifact of an average measurement and is swamped by the larger spikes
occuring in real time. Interestingly, the extensive 30-page Motorola
zener writeup with 60 graphs and tables, etc. ignores the possibility.
Also, their "zener voltage vs zener current" graphs in the 500mW data
sheet show curves of zener voltage over a 10uA to 20mA current range
for zener values from 2.4V to 220V. None of the 46 curves reveals a
negative-resistance region.

In their older literature, Motorola has an interesting voltage-noise
vs zener-voltage curve, which shows a strong peak near 15 to 20V, with
a noise density of 2500 uV/Hz^1/2 at 15V. Yes, 2.5mV - Hah! That works
out to 2.5V rms for a 1MHz bandwidth - I better recheck that number!

James P. Meyer

unread,
Aug 2, 1997, 3:00:00 AM8/2/97
to

On 2 Aug 1997, Winfield Hill wrote:

> OK, sheer WAG speculation hat ON.
> Let's assume a single localized event and estimate the thermal
> spreading distance at say 20 microns in 10ns (check this later).

What would you estimate to be the thickness of the active part
of the junction at the applied voltage?

Jim

slo...@sci.kun.nl

unread,
Aug 2, 1997, 3:00:00 AM8/2/97
to Winfield Hill

In article <5ru8qo$2...@fridge-nf0.shore.net>,

So here is my over-simplification - I was trying to avoid postulating
different M_n and M_p terms. I've got to change my assertion to

A stable (self-sustainging) avalanche process giving a stable current
has (to have) an avalanche gain of one (for the charge carrier with the
lower avalanche gain)- each (positive?) charge carrier on average (has
to) generate one new positive charge carrier.

From Win's earlier post, this means operating at a voltage difference
where each (negative?) charge carrier generates 125 electrons(?). If Win
could expand his references to Thornton and Gandi - are they cited in
AoE? - one might be able to see how general applicable this ratio is.

Thus the avalanche current flows in more or less discrete lumps of
typically 125 electrons (standard deviation +/-11 electrons), and the
noise level is root 125 times 1.09 (about 12) times worse than you'd get
with single independent electrons. Still entirely predictable, if you can
put a number on the ratio of ionisation rates.

>
> Few speculate in detail about the origination of carriers to start the
> process, but all agree the factor M may be quite large, so one single
> electron can generate quite a flood. In one noisy 15V zener, I have
> measured typically 90 million electrons/event, and even up to nearly
> 500 million (more about that later). Do these events start with one
> single carrier, perhaps at a surface defect? If so, the statistical
> speculations I put forward, to which you object, Bill, are completely
> appropriate.

The charge carrier to start the process is most likely the thermally
generated charge carriers responsible for the leakage current through the
diode at low reverse voltages ( from 1V to say 80% of the avalanche
voltage, where multiplication is negligible).

Once the self-sustaining avalanche is under way, it generates its own
charge carriers. If we must make analogies with photodetectors, a zener
diode is operating in the "Geiger mode" as used in SPAD - single photo
avalanche - diodes as opposed to the non-self-sustaining multiplication
mode used in avalanche photo-diodes and photomultiplier tubes.

The maximum gain of simple avalanche photodiodes and PMT's has to be
limited to the region where the feedback from anode back to photo-cathode
is less than one, otherwise you haven't got a detector any more - just a
dead expensive zener diode or its vacuum tube equivalent.

> BTW, as far as I can tell, Bill, no "unstable avalanche ... susceptible
> to entraining by a medium Q resonator" is required.

It is required to explain the results seen by Tony Williams and Jeroen
Belleman. It may be required to explain the noise on real zener diodes
above 8V. How is it that Linear Technology and National Semiconductor can
make "buried" and "sub-surface"zeners that are a lot quieter than
classical (1N823 - 1N827) type reference zeners? Okay - these operate
below 8V with a tunnelling component in the multiplication process.

Tony Williams

unread,
Aug 3, 1997, 3:00:00 AM8/3/97
to

In article <5rvlb0$p...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:

> Below, the results of a few hours spent writing up a few minutes of
> observation yesterday!
>
> The first zener diode I chose showed an incredibly strong relaxation-
> oscillation effect, just as Tony described. It was a Motorola 1N5245B
> with manufacturing code 939. This is a 15V 5% 1/2W zener with a small
> opaque-grey glass body. Interestingly, the next diode in the 1N5245B
> drawer showed little or no effect, so I went back to the first one for
> a detailed examination.

Good News is a second confirmation of what I have been seeing.
Bad News is that he does a much more professional job of
observation and interpretation than I have done.


> The amplitude of the spikes increased as I increased the current,
> peaking around 50uA, where I took some more detailed measurements.
>
> /| 1N5245B at 50uA
> 200mV FS / |
> /| / | /|
> /| / | /| / | /| / | /|
> / | /| / | / | / | /| / | / |/ | /| _____
> | / |/ | /| / |/| / |/ | / |/ | / |/ |
> |/ | / |/ |/|/ |/ | /|/ |
> |/ |/ |
> /
> scope trace, continuous events, 10us FS 14.41 V
> average value

Agree with the picture at low shunt-C, but at higher C the bottoms
of the discharges start to sit at less random voltages.

Now why is "50uA" the magic number? Is it even maybe that setting to
50uA is just a good way of getting the optimum voltage for this discharge
to happen?



> Spike charge and energy. At low currents, say below 5uA, this diode
> seemed happy enough in its (avalanche) discharge, but at higher
> currents the spike events would start, but in a curious way.
>
> The charge slope, which is 140mV/us, implies a circuit capacitance
> (zener and cable) of about 314pF, but measuring this by adding a
> 1000pF 2% cap in parallel showed an actual effective value of 217pF
> (much higher than Motorola's typical values). For example, at 50uA,
> apparently a steady non-event current of about 20uA is always flowing
> and attempts to force higher currents through the zener are ignored,
> but for no more than a hundred nanoseconds, or so. First the ignored
> 30uA steadily charges the capacitance to a higher voltage. Then
> suddenly some location inside the zener aggressively avalanches with
> a discharge step ranging from -10 to -200mV, taking less than 10ns
> (the limit of the scope I was using).
>
> Electrons per event. We see that the discharge suddenly grabs up to
> 315pF * 205mV = 65pC from the capacitance, implying up to 6mA currents
> and 400 million electrons in the event. The discharge events average
> 90 million electrons, and few are less than 1/2 that.
>

I am not in full agreement with your interpretation above.

1. At higher shunt-C the discharges are clearly exponential and I
have earlier reported that discharges appeared to come from about
500 ohms source-R for my 10v zener. (Thin ice here) Would this not
imply that the number of electrons available for discharge is not
a fixed quantity? Even to the extent of saying that the electron
flow is dependant on voltage, dynamically during a discharge?

2. I also tried to estimate how much of the 50uA was used for
charging versus how much was going through the zener as a
"dc-leakage". My sums said that almost all the 50uA was being used
for charging and I saw nothing like your 20/30uA split. Will go
back and have a more careful look at that.

3. I am in agreement with the apparent anomolies when measuring
stray+diode capacitance, but feel slightly uncomfortable about it.
Perhaps there is something there that needs explaining.

> Spike period and statistics. The event-discharge time intervals are
> quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
> min/max). Observing with a 10us window, I _always_ count from 12 to
> 15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
> the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.

This is a very variable characteristic, pick up any zener and you
get different degrees of "activity". The variable seems to be
the voltage range of pk-pk "avalanchers" that any diode has.

> This is more like a relaxation oscillator with a noisy threshold and
> a noisy discharge step, and less like a chaotic or random process.

Perfectly correct, but the randomness in the size of the avalanches
is the thing that makes it appear to produce random noise. Or are
you implying that there may be a discrete number of avalanche sites
and it is therefore not as random as it seems?



> Temperature. Hmmm, at 50uA the diode is dissipates about 0.75mW on
> average, but the power during a 10ns step is about 90mW. Can this
> miniscule 0.9nJ pulse of energy taken from the capacitance have any
> effect? 500mW zeners are transient rated for 20W/1ms = 20mJ, which
> presumably changes the junction temperature by say +150C. We can
> adjust for our 10ns pulse: sqrt(10ns/1ms) * 20mJ => 60uJ/150C, and
> obtain a +2.5 C/uJ temperature-rise for the whole junction at 10ns.
>
> OK, sheer WAG speculation hat ON.
> Let's assume a single localized event and estimate the thermal
> spreading distance at say 20 microns in 10ns (check this later).
> We guess that less than 0.5ppm of the junction area is available
> to absorb energy during the event, leading to an instantaneous
> micro-localized temperature rise of say +450C. This would increase
> the number of intrinsic carriers available by 500x, exceeding the
> doped level, and creating a "mesoplasma" current discharge.
> Note that damaging mesoplasmas must be at much higher temperatures
> (core well over 1000C) for a much longer time to do any damage.
> Speculation hat OFF.

This is outside my competance and I am interested to see where
this speculation/argument leads to.

>
> Higher currents. Upon increasing the current above 75uA, the "normal"
> quiet diode avalanche process asserts itself more strongly and the
> "voltage soar with negative-return spiking" occurs less often.
>
> ,| | |, | , ___+150mV
> |||| ||: || |
> |||| |, |||| ||:||
> ,._,.-,-_.,I||I,-.I|L|,_.-,_,._,.-||II,._,.-,-I||II|, __ 0mV
>
> scope trace at 100uA, scattered events (5us/div)
>
> Negative resistance. Curiously, the voltage is _reduced_ at higher
> currents, as measured by an integrating DVM. This is because the
> soar-with-spike-discharge bursts occur less frequently, slightly
> reducing the average voltage. For example, my 1N5245 dropped about
> 40mV before resuming normal zener impedance properties.

My C10 produces another shape before this one, a tendency for those
relaxation triangles to get flat tops and bottoms. Then it goes
into the above (what I called Mode.4) and it also reduces in amplitude
as you describe. This last mode of osc is quite aggressive, it has
the capability to kick a 10uF capacitor and is my reason for a new
doubt about the traditional advice of "stick a 0.1 across it".

I have previously speculated that a new timing mech may also be coming
into play here.... each of the spikes are followed by a dwell period
and perhaps these are the result of each discharge having enough joules
to kick the local die temperature into a non-osc state temporarily.
This would tie up with the reduction of the osc at higher currents.

>
> continuous events (large)
> volts continuous events /
> 14.41 - (small) __,..-=--,,.__ scattered events
> 14.40 - \ _,.-'~'`` `'-.,_ /
> 14.39 - _,-'` '-,_ rare events
> 14.38 - ,-'` '-,_ \
> 14.37 - / ``''===----
> 14.36 - | | | / | | |
> 20 uA 50 75 / 100 150 200
> current -> /
> /
> "negative-resistance" region
> Zener voltage goes down with increasing current.
>
> I'm not inclined to make much of this "negative-resistance" region,
> especially as a possible oscillator component, since it's just an
> artifact of an average measurement and is swamped by the larger spikes
> occuring in real time. Interestingly, the extensive 30-page Motorola
> zener writeup with 60 graphs and tables, etc. ignores the possibility.
> Also, their "zener voltage vs zener current" graphs in the 500mW data
> sheet show curves of zener voltage over a 10uA to 20mA current range
> for zener values from 2.4V to 220V. None of the 46 curves reveals a
> negative-resistance region.

Agree with the curve above, except that there is also a "rare-events"
region at very low current in many, but not all, zeners.

>
> In their older literature, Motorola has an interesting voltage-noise
> vs zener-voltage curve, which shows a strong peak near 15 to 20V, with
> a noise density of 2500 uV/Hz^1/2 at 15V. Yes, 2.5mV - Hah! That works
> out to 2.5V rms for a 1MHz bandwidth - I better recheck that number!

No comment.

Winfield Hill

unread,
Aug 3, 1997, 3:00:00 AM8/3/97
to

slo...@sci.kun.nl, <slo...@sci.kun.nl> said...

>
>In article <5ru8qo$2...@fridge-nf0.shore.net>,
> hi...@rowland.org (Winfield Hill) wrote:
>>
>> Bill Sloman, <slo...@sci.kun.nl> said...
>>-> [snip]
>>-> Despite Winfield Hill's opinion on the subject, a stable avalanche
>>-> process giving a stable current has an avalanche gain of one - each
>>-> charge carrier on average generates one new charge carrier, ...

>>
>> Some of a zener-diode's current is no doubt associated with low
>> avalanche gains, but I certainly haven't advanced any opinions about
>> that. In fact, my understanding is much higher gains than unity are
>> usually associated with avalanche processes. This is the argument put
>> forward in the old Motorola literature, complete with a nice drawing.
>>
>> Let's review what Gandi says (I'll condense): Under the condition of
>> high electric fields, the velocity of individual carriers will exceed
>> their terminal drift velocity ... and become "hot" carriers. These

>> have sufficient energy in a collision to promote valence-band
>> electrons to the conduction band, creating a hole-electron pair. The
>> impact ionization effect is multiplicative, with newly-generated holes
>> or electrons involved in the ionization of further hole-electron pairs.
>>
>> Most authorities, e.g. Thornton et.al. derive a multiplication factor,
>> M, e.g., with 1/M = 1 - (V/Vbr)^n where n = 1.5 to 6.5. We see that
>> M -> infinity as V -> the breakdown voltage, V_br. Some, e.g. Ghandi,
>> start with ionization coefficients for the number of hole-electron
>> pairs produced per-carrier per-cm traveled in the E-field, integrating,
>> etc., to develop separate M_n and M_p terms for the electron and hole
>> carriers, etc. entering a depletion layer. Even with different
>> exponents (4 and 6 resp), in the end they get similar results.
>
> So here is my over-simplification - I was trying to avoid postulating
> different M_n and M_p terms. I've got to change my assertion to
>
> A stable (self-sustainging) avalanche process giving a stable current
> has (to have) an avalanche gain of one (for the charge carrier with the
> lower avalanche gain)- each (positive?) charge carrier on average (has
> to) generate one new positive charge carrier.
>
> From Win's earlier post, this means operating at a voltage difference
> where each (negative?) charge carrier generates 125 electrons(?). If Win
> could expand his references to Thornton and Gandi ...

Bill, I don't have a very good reference library here at home, and I have
limited time at work to make usenet postings, but I would like to answer
from memory and try to set some things straight.

Gandi wrote a book called "Semiconductor Power Devices", and Thornton
et.al. wrote "Characteristics and Limitations of Transistors," However
any detailed discussion of avalanche breakdown physics should mirror the
arguments there. In the small sampling I have done, in what I suspect is
an extensive literature, I have seen several quite different derivative
approaches, but generally with similar results.

I don't recall having ever seen any M = 1 argumemts before yours. Can
you provide a reference to the effect you're thinking of? Are we perhaps
using different terms? At low electric fields, mobile carriers are
insufficiently accelerated before collisions to be capable of ionization,
however at sufficiently high electric fields, carriers can accelerate
enough to be capable of ionizating collisions and are "hot carriers."
For moderate electric field strengths, creating a depletion-layer width
just above the mean-free path length, hot-carrier collisions may produce
just one new electron-hole pair for each collision, but the new carriers
are accelerated and also become hot carriers making more ionizing
collisions, etc. The avalanche multiplication factor, M, is the total
number of carriers traversing the depletion region, resulting from one
single starting carrier. There's no doubt M is _much_ more than unity,
to be of any interest.

The "breakdown" voltage is usually defined as M = infinity, but the
stable increased "leakage" currents we see at high voltages below
breakdown, must also correspond to large M, but well below infinity!
We're no doubt slightly below the "bulk" breakdown voltage for modest
zener currents, except perhaps for a few small regions of the diode.

In semiconductor device equations, I suppose any value above M = 0 is
an "avalanche gain", however only much higher gains can produce currents
significantly above the usual low-voltage leakage current. What argument
do you use to show unstable currents if M is larger than unity?
Certainly a PMT tube has a reasonably stable gain with a very high M,
like 2x10^6 at 1kV for one tube. The value M = 125 I used at one point
was picked out of a hat for speculation, as was clear.

> The charge carrier to start the process is most likely the thermally
> generated charge carriers responsible for the leakage current through
> the diode at low reverse voltages ( from 1V to say 80% of the avalanche
> voltage, where multiplication is negligible).

I don't know much about the doping of classic zener diodes, but for other
semiconductor devices, generally the current from doping is much higher
than the thermally-generated current. Only at some rather high
temperature will the thermally-generated carrier density surpass the
mobile carriers. E.g. a MOSFET with a heavily-doped p+ "zener"
breakdown-protection well (which keeps avalanche currents away from the
gate area) has say 2.5E15 atoms/cm^3 and an intrinsic temperature of 360C.

> Once the self-sustaining avalanche is under way, it generates its own

> charge carriers. ...

I'm uncomfortable with labelling any increase in conductivity, due to
M >> 1 avalanche gain, a self-sustaining process. [E.g. I wouldn't
call the continuing current in a resistor, due to its conductivity, a
self-sustaining process.] Sure M = infinity is self sustaining, but if
occurring in very small regions of the junction, it's likely a starting
point for a highly-localized mesoplasma thermal runaway (e.g. above 360C
for the MOSFET above), which I'd rather call by its proper name, and
which may be quickly extinquished by natural means.

> The maximum gain of simple avalanche photodiodes and PMT's has to be
> limited to the region where the feedback from anode back to photo-cathode
> is less than one, otherwise you haven't got a detector any more - just a
> dead expensive zener diode or its vacuum tube equivalent.

Aha. A photoelectron accelerated in a vacuum, smashing into a dynode and
creating a flood of secondary electrons is a different beast entirely.
Are you introducing here the concept of a positively-charged secondary
particle reverse-accelerated by the E-field to strike the photocathode?

>> BTW, as far as I can tell, Bill, no "unstable avalanche ...
>> susceptible to entraining by a medium Q resonator" is required.

> It is required to explain the results seen by Tony Williams and Jeroen
> Belleman. It may be required to explain the noise on real zener diodes
> above 8V.

Bill, a "medium Q resonator" or any other reonator, certainly isn't
required to see what I saw last Friday, replicating Tony's observations.
Your term "unstable avalanche" is descriptive, but misleading. See my
two follow-on posts to Tony for some rather different thought processes,
neither of which well fits the term "unstable" to my mind. First my WAG
"mesoplasma" current-discharge calculations, and second a Motorola
reference to a "microplasma discharge" theory.

> How is it that Linear Technology and National Semiconductor can
> make "buried" and "sub-surface"zeners that are a lot quieter than
> classical (1N823 - 1N827) type reference zeners? Okay - these operate
> below 8V with a tunnelling component in the multiplication process.

The tunnelling-current component certainly helps, but careful control of
all the mobile-carrier sources is a usual reason for surface passivation
or buried structures. Motorola talks about using a highly-doped
phosphosilicate glass layer to act as a "getter" during manufacturing,
diffusing contaminants away from the junction.

Winfield Hill

unread,
Aug 3, 1997, 3:00:00 AM8/3/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...

>
> Winfield Hill <hi...@rowland.org> wrote:
>
>> The first zener diode I chose showed an incredibly strong relaxation-
>> oscillation effect, just as Tony described. It was a Motorola 1N5245B
>> with manufacturing code 939. This is a 15V 5% 1/2W zener with a small
>> opaque-grey glass body. ...

>
> Good News is a second confirmation of what I have been seeing.

Haven't some others chimed as well, confirming your observations?

>> The amplitude of the spikes increased as I increased the current,
>> peaking around 50uA, where I took some more detailed measurements.
>>
>> /| 1N5245B at 50uA
>> 200mV FS / |
>> /| / | /|
>> /| / | /| / | /| / | /|
>> / | /| / | / | / | /| / | / |/ | /| _____
>> | / |/ | /| / |/| / |/ | / |/ | / |/ |
>> |/ | / |/ |/|/ |/ | /|/ |
>> |/ |/ |
>> /
>> scope trace, continuous events, 10us FS 14.41 V
>> average value
>
> Agree with the picture at low shunt-C, but at higher C the bottoms
> of the discharges start to sit at less random voltages.

Hmm, interesting. I only glanced at higher C (1300pF total) and saw
greatly reduced negative step amplitudes, or many fewer steps.

> Now why is "50uA" the magic number?

It isn't - it's a continuoum function, peaking near 50uA for my part.

>> effective value of 217pF (much higher than Motorola's typical values).

To compare with Motorola's typical curve, we can subtract say 130pF of
scope and cable capacitance, but we still get around 90pF, or 3x what
they imply. This deserves further examination.

>> ... at 50uA,apparently a steady non-event current of about 20uA is
>> always flowing and ... higher currents .. are ignored, 30uA steadily


>> charges the capacitance to a higher voltage. Then suddenly some
>> location inside the zener aggressively avalanches with a discharge

>> step ranging from -10 to -200mV, taking less than 10ns...


>
> I am not in full agreement with your interpretation above.
>
> 1. At higher shunt-C the discharges are clearly exponential and I
> have earlier reported that discharges appeared to come from about
> 500 ohms source-R for my 10v zener.

Ahh, great! That would be imply a discharge current of 10 to 20mA - in
the same ballpark as the 6mA I estimated for 10ns. If my discharge was
really in 3 to 5 ns, we actually have matching event-size observations.

> 2. ... almost all the 50uA was being used for charging and I saw


> nothing like your 20/30uA split.

I'm not surprised - I'll bet that varies entirely part-to-part.

>> Spike period and statistics. The event-discharge time intervals are
>> quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
>> min/max). Observing with a 10us window, I _always_ count from 12 to
>> 15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
>> the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.
>
> This is a very variable characteristic, pick up any zener and you
> get different degrees of "activity". The variable seems to be
> the voltage range of pk-pk "avalanchers" that any diode has.

Tony, I wonder if you also observe the anomolous statistics?

>> This is more like a relaxation oscillator with a noisy threshold and
>> a noisy discharge step, and less like a chaotic or random process.
>
> Perfectly correct, but the randomness in the size of the avalanches
> is the thing that makes it appear to produce random noise. Or are
> you implying that there may be a discrete number of avalanche sites
> and it is therefore not as random as it seems?

Yes, I think at the low current we're considering, we really are seeing a
crude type of relaxation oscillator with perhaps only a few active sites
involved. In these devices, when the current charges the voltage above
some slightly noisy threshold (varying no more than 50mV in my case), a
microplasma discharge avalanche is triggered, discharging a somewhat
indeterminant amount of charge before stopping. Then the process starts
all over - just like a relaxation oscillator. See below.

>> Temperature. Hmmm, at 50uA the diode is dissipates about 0.75mW on
>> average, but the power during a 10ns step is about 90mW. Can this
>> miniscule 0.9nJ pulse of energy taken from the capacitance have any
>> effect? 500mW zeners are transient rated for 20W/1ms = 20mJ, which
>> presumably changes the junction temperature by say +150C. We can
>> adjust for our 10ns pulse: sqrt(10ns/1ms) * 20mJ => 60uJ/150C, and
>> obtain a +2.5 C/uJ temperature-rise for the whole junction at 10ns.
>>
>> OK, sheer WAG speculation hat ON.
>> Let's assume a single localized event and estimate the thermal
>> spreading distance at say 20 microns in 10ns (check this later).
>> We guess that less than 0.5ppm of the junction area is available
>> to absorb energy during the event, leading to an instantaneous
>> micro-localized temperature rise of say +450C. This would increase
>> the number of intrinsic carriers available by 500x, exceeding the
>> doped level, and creating a "mesoplasma" current discharge.
>> Note that damaging mesoplasmas must be at much higher temperatures
>> (core well over 1000C) for a much longer time to do any damage.
>> Speculation hat OFF.

Tony, I came across some very interesting remarks in Chapter 4 of the
material in the Motorola TVS/Zener databook (1994 edition, page 11-18):

"Between the minimum currents shown in Figure 4 and the


leakage currents, there is the "knee" region. The avalanche
mechanism may not occur simultaneously across the entire area
of the P-N junction, but first at one microscopic site, then
at an increasing number of sites as further voltage is applied.
This action can be accounted for by the "microplasma discharge"

theory and correlates with several breakdown characteristics.
"An exaggerated view of the knee region is shown in Figure 5.
As can be seen, the breakdown or avalanche current does not
increase suddenly, but consists of smoothly rising current
versus increments each with a sudden break point.
"At the lowest point, the zener resistance (slope of the
curve) would test high, but as current continues to climb,
the resistance decreases. It is as though each discharge site
has a high resistance with each succeeding site being in
parallel until the total resustance is very small.
"In addition to the resistive effects, the micro plasmas may
act as noise generators. The exact process of manufacturing
affects how high the noise will be, but in any event there will
be some noise at the knee, and it will diminish considerably as
current is allowed to increase."

My comment: The "resistance knee" arguments don't exactly square up
with our observations, but the "microscopic sites" contributing parallel
avalanche pathways cetainly does! Too bad they don't pass along any
references to the "microplasma discharge" theory!

>> Higher currents. Upon increasing the current above 75uA, the
>> "normal" quiet diode avalanche process asserts itself more strongly
>> and the "voltage soar with negative-return spiking" occurs less often.
>>
>> ,| | |, | , ___+150mV
>> |||| ||: || |
>> |||| |, |||| ||:||
>> ,._,.-,-_.,I||I,-.I|L|,_.-,_,._,.-||II,._,.-,-I||II|, __ 0mV
>>
>> scope trace at 100uA, scattered events (5us/div)
>>
>> Negative resistance. Curiously, the voltage is _reduced_ at higher
>> currents, as measured by an integrating DVM. This is because the
>> soar-with-spike-discharge bursts occur less frequently, slightly
>> reducing the average voltage. For example, my 1N5245 dropped about
>> 40mV before resuming normal zener impedance properties.
>
> My C10 produces another shape before this one, a tendency for those
> relaxation triangles to get flat tops and bottoms. Then it goes
> into the above (what I called Mode.4) and it also reduces in amplitude
> as you describe.

Yes. I didn't observe a spike-amplitude reduction so much as a greatly
reduced frequency of occurance. It's the average voltage that drops.

> This last mode of osc is quite aggressive, it has the capability to
> kick a 10uF capacitor and is my reason for a new doubt about the
> traditional advice of "stick a 0.1 across it".

Interesting. Just how big is the 10uF kick? Maybe the microplasm
discharge can be much more energetic if a bigger capacitor is available
to continue forcing the higher voltage while supplying much more energy.

> I have previously speculated that a new timing mech may also be coming
> into play here.... each of the spikes are followed by a dwell period
> and perhaps these are the result of each discharge having enough joules
> to kick the local die temperature into a non-osc state temporarily.
> This would tie up with the reduction of the osc at higher currents.

Although a WAG estimate gives surprisingly high micro-region temperatures
for a <10ns discharge, afterwards surely it must rapidly drop as the heat
spreads, returning to normal levels long before the next event starts.

Tony, I find this all very interesting. I'm surprised more isn't said
about it in the literature and also that I didn't think of checking it
before myself. Thanks much.

Tony Williams

unread,
Aug 4, 1997, 3:00:00 AM8/4/97
to

In article <5s2t1s$2...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:

Have some results of more careful measurements, taken over lunch.

1. A re-look at stray capacitance, Cs, and I-leakage sideways loss
of current when charging at 50uA.

I carefully timed a 60mV section of the reasonably linear recharge ramp
for 4700pF and 9400pF 1% external shunt-Cs. I got 7.8uS and 15uS.

sum.1 [4700pF + Cs] * 60mV = [50uA - I-leakage] * 7.8uS

sum.2 [9400pF + Cs] * 60mV = [50uA - I-leakage] * 15uS

Subtracting [sum2 - sum1] gives I-leakage = 10.8uA.
------------------

Putting I-leakage into either sum gives Cs = 392pF
----------

The caution to be drawn here is that it does not take much error in
the timing measurements to send the results well off-beam.

[Win said]


> >> effective value of 217pF (much higher than Motorola's typical values).
>
> To compare with Motorola's typical curve, we can subtract say 130pF of
> scope and cable capacitance, but we still get around 90pF, or 3x what
> they imply. This deserves further examination.
>
> >> ... at 50uA,apparently a steady non-event current of about 20uA is
> >> always flowing and ... higher currents .. are ignored, 30uA steadily
> >> charges the capacitance to a higher voltage. Then suddenly some
> >> location inside the zener aggressively avalanches with a discharge
> >> step ranging from -10 to -200mV, taking less than 10ns...

[me]


> > 2. ... almost all the 50uA was being used for charging and I saw
> > nothing like your 20/30uA split.


Ok Win, you got 217pF/20uA and I got 392pF/11uA for different diodes,
so we *are* singing off the same songsheet here.
-------------------------------------------------------------------------

2. A re-look at the discharge shape and timings.

I timed the discharges for various external (shunt-C + Cstray).
The discharge is exponential in shape and my best guess is that
it is >RC and <2RC. So I give source-R sums for both, RC first.

1000+392pF = 0.7uS (approx)... R-source= 503 to 251 ohms.

4700+392 = 2.5uS.............. R-source= 491 to 245 ohms.

9400+392 = 5uS................ R-source= 511 to 255 ohms.

> > 1. At higher shunt-C the discharges are clearly exponential and I
> > have earlier reported that discharges appeared to come from about
> > 500 ohms source-R for my 10v zener.

[Win]


> Ahh, great! That would be imply a discharge current of 10 to 20mA - in
> the same ballpark as the 6mA I estimated for 10ns. If my discharge was
> really in 3 to 5 ns, we actually have matching event-size observations.

I am unhappy with that 6mA and 20mA, especially your derivation of I
by simply calculating Vzener/500ohms. I don't think the microavalanches
are aiming towards 0v at all.

If you assume the "RC to 2RC" estimate is about right you can take
V = Vpk e^-T/RC and substitute RC or 2RC for T and set V = (Vpk - 90mV)
in order to get an estimate of a Vpk aiming voltage for the RC discharge.

That gives Vpks around 120/130mV and Ipks of 125mV/500, 250uA.
That is one twelth of your estimate.

I don't have a current probe, but stuck a 2-ohm resistor in series
with the 0v end of the cap. 1mA Ipk would produce 2mV, which I should
be able to see on the scope at 5mv/div. There was nothing visible.

-----+ +----- +50uA
| |
| | _____-50uA This is the current through a 100R
| / in series with 9400pF. It confirms
| / the estimate of 250uA.
| /
| /
|/_____________ -200/-300uA, mostly -280uA.

(Note, this current waveform gives me a problem. I can clearly
see a charging current of +50uA in the cap. But I have "proved"
above that it should be about 11uA less than that. Hmm, looking at
Ipk = -280 v Imin= -50uA suggests I should redo the RC or 2RC estimate.)
-------------------------------------------------------------------------

> > This last mode of osc is quite aggressive, it has the capability to
> > kick a 10uF capacitor and is my reason for a new doubt about the
> > traditional advice of "stick a 0.1 across it".
>
> Interesting. Just how big is the 10uF kick? Maybe the microplasm
> discharge can be much more energetic if a bigger capacitor is available
> to continue forcing the higher voltage while supplying much more energy.
>

Ok, Results are:- 10uF/134uA, 3 to 5mV pk-pk. 2u2/154uA, 5 to 9mV pk-pk.
-------------------------------------------------------------------------

> >> Spike period and statistics. The event-discharge time intervals are
> >> quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
> >> min/max). Observing with a 10us window, I _always_ count from 12 to
> >> 15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
> >> the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.
> >
> > This is a very variable characteristic, pick up any zener and you
> > get different degrees of "activity". The variable seems to be
> > the voltage range of pk-pk "avalanchers" that any diode has.
>
> Tony, I wonder if you also observe the anomolous statistics?

My scope (or my eyesight) is not good enough to do that. However,
watching it for long periods does suggest a pattern. Most of the
pk-pks live within a certain band, together with occasional
excursions well outside the band.

I should point out here that added shunt-C does reduce the
pk-pk variations dramatically. At just 4700pF most of the
excursions are about 90mV pk-pk.
-------------------------------------------------------------------------

> Yes, I think at the low current we're considering, we really are seeing a
> crude type of relaxation oscillator with perhaps only a few active sites
> involved. In these devices, when the current charges the voltage above
> some slightly noisy threshold (varying no more than 50mV in my case), a
> microplasma discharge avalanche is triggered, discharging a somewhat
> indeterminant amount of charge before stopping. Then the process starts
> all over - just like a relaxation oscillator. See below.

I believe that your observation is correct. Carefully watching waveforms,
suggests that your 10/12 discharge-sites is not far off for 0pF, reducing
to 4 to 6 sites for 4700pF. Best guesses only.
-------------------------------------------------------------------------

> Tony, I find this all very interesting. I'm surprised more isn't said
> about it in the literature and also that I didn't think of checking it
> before myself. Thanks much.

It *is* interesting, and so easy to do. I suspect that it is
well documented somewhere though. Perhaps that fact that it
appears to be so unpredictable as to have no application is the
reason for having little in the literature.

slo...@sci.kun.nl

unread,
Aug 4, 1997, 3:00:00 AM8/4/97
to Winfield Hill

In article <5s2t2c$2...@fridge-nf0.shore.net>,
hi...@rowland.org (Winfield Hill) wrote:

< big snip >

> I don't recall having ever seen any M = 1 argumemts before yours. Can
> you provide a reference to the effect you're thinking of?

The argument is well known in chemical kinetics, and was first used by
Hinshellwood and Lindeman in the 1920's. I couldn't find the original
reference when I was writing my Ph.D. thesis, so I'm not going to try
now.

The essential idea is that a chemical reaction proceeding at a definite
rate, or an avalanche process transfering a definite current is a
quasi-equilibrium. If it weren't, the reaction rate or the avalanche
current would change very rapidly. If you dig deeper, the essential
assumption is that the process of chemical change or avalanche gain is
much faster than the changes in reaction rate or avalanche current at
which you are looking.

The avalanche process in IMPATT diodes is used to generate 30GHz
oscillations, so it would seem to be faster than 5psec.

In this context, if the avalanche current is to remain stable from
nanosecond to nansecond, the rate at which holes regenerate hole-electron
conductor pairs has to be almost exactly equal to one. The fact that
electrons generate - say - 125 hole-electron pairs means that the
avalanche is sustained if just one of those holes generates one
hole-electron pair on the other side of the junction, so an individual
hole then only needs a 0.8% chance of generating a hole-electronpair to
sustain the avalanche. To sustain a "stable" avalanche it must have
exactly that chance of generating a hole-electron pair.

> Are we perhaps using different terms? At low electric fields, mobile
> carriers are insufficiently accelerated before collisions to be capable
> of ionization, however at sufficiently high electric fields, carriers can
> accelerate enough to be capable of ionizating collisions and are "hot
> carriers." For moderate electric field strengths, creating a
> depletion-layer width just above the mean-free path length, hot-carrier
> collisions may produce just one new electron-hole pair for each collision,
> but the new carriers are accelerated and also become hot carriers making
> more ionizing collisions, etc. The avalanche multiplication factor, M, is
> the total number of carriers traversing the depletion region, resulting from
> one single starting carrier. There's no doubt M is _much_ more than unity,
> to be of any interest.
>
> The "breakdown" voltage is usually defined as M = infinity, but the
> stable increased "leakage" currents we see at high voltages below
> breakdown, must also correspond to large M, but well below infinity!

In fact, well below unity for the less effective carrier.

> We're no doubt slightly below the "bulk" breakdown voltage for modest
> zener currents, except perhaps for a few small regions of the diode.
>
> In semiconductor device equations, I suppose any value above M = 0 is
> an "avalanche gain", however only much higher gains can produce currents
> significantly above the usual low-voltage leakage current. What argument
> do you use to show unstable currents if M is larger than unity?

> Certainly a PMT tube has a reasonably stable gain with a very high M,
> like 2x10^6 at 1kV for one tube.

And if you try to run a higher gain, the occasional positive ion produced
at the anode gets back to the photocathode, producing more electrons,
which ionise more of the (tiny amount of) residual gas left in the tube
to produce more postive ions ....

> The value M = 125 I used at one point
> was picked out of a hat for speculation, as was clear.

But it ties up very nicely with the maximum stable gain you can get out of
an avalanche photodiode.

> > The charge carrier to start the process is most likely the thermally
> > generated charge carriers responsible for the leakage current through
> > the diode at low reverse voltages ( from 1V to say 80% of the avalanche
> > voltage, where multiplication is negligible).
>
> I don't know much about the doping of classic zener diodes, but for other
> semiconductor devices, generally the current from doping is much higher
> than the thermally-generated current. Only at some rather high
> temperature will the thermally-generated carrier density surpass the
> mobile carriers. E.g. a MOSFET with a heavily-doped p+ "zener"
> breakdown-protection well (which keeps avalanche currents away from the
> gate area) has say 2.5E15 atoms/cm^3 and an intrinsic temperature of 360C.

Yes, but in a zener diode near avalanche the biassing keeps the intrinsic
charge carriers in places where they can't carry any current. This is
why a P/N junction is effective as a rectifier ...

> > Once the self-sustaining avalanche is under way, it generates its own
> > charge carriers. ...
>
> I'm uncomfortable with labelling any increase in conductivity, due to
> M >> 1 avalanche gain, a self-sustaining process. [E.g. I wouldn't
> call the continuing current in a resistor, due to its conductivity, a
> self-sustaining process.]

Neither would I. Resistor are conductors, with fully populated conduction
bands.

> Sure M = infinity is self sustaining,

Not merely self-sustaining, but massively increasing!

> but if
> occurring in very small regions of the junction, it's likely a starting
> point for a highly-localized mesoplasma thermal runaway (e.g. above 360C
> for the MOSFET above), which I'd rather call by its proper name, and
> which may be quickly extinquished by natural means.

I don't see what postulating a "highly-localised mesoplasma thermal
runaway" actually does for you - what does it actually explain?

> > The maximum gain of simple avalanche photodiodes and PMT's has to be
> > limited to the region where the feedback from anode back to photo-cathode
> > is less than one, otherwise you haven't got a detector any more - just a
> > dead expensive zener diode or its vacuum tube equivalent.
>
> Aha. A photoelectron accelerated in a vacuum, smashing into a dynode and
> creating a flood of secondary electrons is a different beast entirely.
> Are you introducing here the concept of a positively-charged secondary
> particle reverse-accelerated by the E-field to strike the photocathode?

Yes, see above.

> >> BTW, as far as I can tell, Bill, no "unstable avalanche ...
> >> susceptible to entraining by a medium Q resonator" is required.
>
> > It is required to explain the results seen by Tony Williams and Jeroen
> > Belleman. It may be required to explain the noise on real zener diodes
> > above 8V.
>

> Bill, a "medium Q resonator" or any other resonator, certainly isn't


> required to see what I saw last Friday, replicating Tony's observations.

It is necessary to explain Tony's observations with medium Q resonators

> Your term "unstable avalanche" is descriptive, but misleading. See my
> two follow-on posts to Tony for some rather different thought processes,
> neither of which well fits the term "unstable" to my mind. First my WAG
> "mesoplasma" current-discharge calculations, and second a Motorola
> reference to a "microplasma discharge" theory.

Motorola's reference to "microplasma theory" is just two words in the
1980 Motorola Zener Diode catalogue, to which I too have access. Your
"mesoplasma" is worked out in more detail, but strikes me as an
unnecessary.

To explain the low current behaviour you and Tony and Jeroene Belleman
has seen, you need only invoke the idea, clearly expressed in the
literature on "Geiger mode" single photon avalanche diodes (SPADs), that
a sufficiently low avalanche current self-extinguishes due to statistical
fluctuations in the number of holes generated. If you assume that at
100uA current is transferred through a junction with a 1psec propagation
delay, some five holes have to generate hole-electron pairs on the
negative side of the junction every picosecond. Roughly once every
150psec, none of them will make it, and the avalanche will be
extinguished.

The current from your bias resistor then charges up the diode capacitance
(and any other capacitance that is handy)until thermal excitation
produces a charge carrier. See Robert J.McIntryre "On the Avalanche
Initiation Probability of Avalanche Diodes Above the Breakdown Voltage"
IEEE ED-20 pages 637-42 (1973). The initiation probablity appears to rise
with voltage, which could explain the relatively low variation in your
charging times.

Once the avalanche is under way the current rises rapidly until circuit
inductance or contact resistance or space charge limit the effective
voltage across the junction to that required to maintain a stable
avalanche.

This current then discharges the capacitance, reducing the voltage across
the junction to give us Tony's exponential decay, until the current is
low enough to spontaneously self-extinguish. As the DC current rises, the
time required for the avalanche to self-extinguish rises quite rapidly -
giving the intermittent voltage spikes seen by Win from 50uA to 75uA and
the "rare" spikes seen out to 200uA.

Simple, and just two assumptions - the self-extinguishing avalanche with
a 1psec wide junction, and some 460,000 avalanche sites to divide the
100uA leakage current into the 0.2pA per site required to explain
13.5+/-1.5 avalanche initiations every 10usec.

Tony's results with big capacitors may be explicable in terms of the
above model and some inductance. We probably need to draw in Motorola's
point that as the current rises more sites become active - I think this
could be explained by modest self-heating (10C or so) in the active
channels.

Mike

unread,
Aug 5, 1997, 3:00:00 AM8/5/97
to

Winfield Hill wrote:
>
> slo...@sci.kun.nl, <slo...@sci.kun.nl> said...
> >
> >In article <5ru8qo$2...@fridge-nf0.shore.net>,
> > hi...@rowland.org (Winfield Hill) wrote:
> >>
> >> Bill Sloman, <slo...@sci.kun.nl> said...
> >>-> [snip]

When I left this discussion, the claim was oscillations in the VHF-UHF
range.

Now, the best you can come up with is surface contamination noise in the
microamp region - slightly above DC!

Winfield - I'm truly sorry you got dragged into this mess - I have been
telling others to watch for your posts, as I felt they were the most
valuable in this newsgroup.

I think everyone got lost on the original post. Who made it?

Best Regards,

Mike

Hosting Jonathan Ramsey's TCP/IP with Pascal source:
http://www.csolve.net/~add/zips/internet.zip (471K)

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
to

Winfield Hill, <hi...@rowland.org> said...

>Tony Williams, <to...@ledelec.demon.co.uk> said...
>> Winfield Hill <hi...@rowland.org> wrote:
>>> incredibly strong relaxation-oscillation effect, just as Tony
>>> described. ... Motorola 1N5245B, code 939. A 15V 5% 1/2W zener...

>>>
>>> /| 1N5245B at 50uA
>>> 200mV FS / |
>>> /| / | /|
>>> /| / | /| / | /| / | /|
>>> / | /| / | / | / | /| / | / |/ | /| _____
>>> | / |/ | /| / |/| / |/ | / |/ | / |/ |
>>> |/ | / |/ |/|/ |/ | /|/ |
>>> |/ |/ |
>>> /
>>> scope trace, continuous events, 10us FS 14.41 V
>>> average value
>>
>> Agree with the picture at low shunt-C, but at higher C the bottoms
>> of the discharges start to sit at less random voltages.
>>> effective value of 217pF (much higher than Motorola's typical values).
>>> [snip]

>>> ... at 50uA,apparently a steady non-event current of about 20uA is
>>> always flowing and ... higher currents .. are ignored, 30uA steadily
>>> charges the capacitance to a higher voltage. Then suddenly some
>>> location inside the zener aggressively avalanches with a discharge
>>> step ranging from -10 to -200mV, taking less than 10ns...
>>
>> I am not in full agreement with your interpretation above.
>>
>> 1. At higher shunt-C the discharges are clearly exponential and I
>> have earlier reported that discharges appeared to come from about
>> 500 ohms source-R for my 10v zener.
>
> Ahh, great! That would be imply a discharge current of 10 to 20mA - in
> the same ballpark as the 6mA I estimated for 10ns. If my discharge was
> really in 3 to 5 ns, we actually have matching event-size observations.

The measurements above were with 160pF of circuit capacitance.

After more careful measurements with my Tek 500MHz scope and 1GHz 1pF FET
probe, I have a slightly different view. With no external capacitance, the
discharge steps appear to have several components, the largest of which is
50 to 550 mV in size and only takes about 1.0ns (corrected). Hmmm, this is
slower than the 0.7ns I measured for the probe/scope combo, and also too
slow to account for by the internal RC of the diode. so perhaps it's a real
time duration.

>> 2. ... almost all the 50uA was being used for charging and I saw
>> nothing like your 20/30uA split.

OK, Tony, now after a careful capacitance measurement of 60pF for my noisy
zener (which doesn't change from a few volts below, up to and into the
avalanche state, etc.), it appears that possibly ALL of its current is made
up of microplasma discharges (as Motorola calls them), just as you
observed.

Calculating the sink current during the 1ns microplasma discharge event, I
get I = C dV/dt = from 5 to 35mA and about 30 to 220 million electrons.
And about E = itV = 0.5nJ of avalanche energy in the biggest 1ns steps,
plus sometimes as much again in the next 4 to 10ns.

Adding parallel capacitance reduced the step sizes, as you said. For
modest capacitances, like 1nF, I still observed an constant-current
discharge. However with a 0.1uF capacitor I saw a 4us exponential RC
discharge decay, as you saw, with the fastest portion taking 1.5us. I
didn't double-check the greatly slowed charging slopes.

total capacitance 60pF 1.06nF 0.1uF
discharge step size -250mV -105mV 23mV
discharge ramp time 1.0ns 26ns 1.5us
calculated sink current 15mA 4.3mA 1.5mA
" avalanche energy 0.22nJ 1.65nJ 34nJ
energy scaled by sqrt(t) 7.0u 10u 28uJ/ns^1/2

>> [snip]


>> This last mode of osc is quite aggressive, it has the capability to
>> kick a 10uF capacitor and is my reason for a new doubt about the
>> traditional advice of "stick a 0.1 across it".

I looked with a big capacitor for some occaisional whopper discharges, as
your part provided, but mine didn't oblige. However, I agree completely
with your scepticism.

>> I have previously speculated that a new timing mech may also be coming

>> into play here.... each of the spikes are followed by a dwell period...

Isn't that just the time required to build the voltage back up to the
microplasma-event threshold level? But I don't know what to make of the
apparently increased "energy scaled by square-root time" with big
capacitors (i.e. the increased temperature-jump potential), shown by the
calculation in the last row. Maybe larger microplasma areas are involved
for longer time durations.

Winfield Hill

unread,
Aug 5, 1997, 3:00:00 AM8/5/97
to

slo...@sci.kun.nl, <slo...@sci.kun.nl> said...

>
>In article <5s2t2c$2...@fridge-nf0.shore.net>,
> hi...@rowland.org (Winfield Hill) wrote:
>
> The essential idea is that a chemical reaction proceeding at a definite
> rate, or an avalanche process transfering a definite current is a
> quasi-equilibrium. If it weren't, the reaction rate or the avalanche
> current would change very rapidly.

Yes, I've heard of that. However, we clearly see that in fact the
avalanche current does change very rapidly.

> The avalanche process in IMPATT diodes is used to generate 30GHz
> oscillations, so it would seem to be faster than 5psec.

Surely the device physics (lifetimes, carrier, impurity and defect
densities, depletion-layer thickness, etc) must be very different for
those diodes. Perhaps the time scales for our jelly-bean zeners are in
the slow sub-ns territory.

> In this context, if the avalanche current is to remain stable from
> nanosecond to nansecond, the rate at which holes regenerate
> hole-electron conductor pairs has to be almost exactly equal to one.

...

Why is it necessary to invoke an important role for both carriers? Can't
the bulk of the avalanche current be from carriers travelling one way?
We're just talking about the multiplication of hot carriers through the
depletion layer. If just below breakdown (say 50mV), the energy of a
significant portion of the carriers fails to reach the ionization
threshold (say 2.5 ev), before experiencing an phonon collision, then we
have a low value of multiplication, M. But at a slightly higher voltage,
this story changes completely, with whole reams of new carriers generated
in many cascading stages for a 15V zener, and a very high M. This would
be a rapidly increasing current, just as we have observed. Perhaps light
is even emitted locally, providing photoelectrons to help the process.

>> Sure M = infinity is self sustaining,
> Not merely self-sustaining, but massively increasing!

Fine, that's what we see. I think M -> to a very high number, at which
point something else provides limiting for the microplasma.

> I don't see what postulating a "highly-localised mesoplasma thermal
> runaway" actually does for you - what does it actually explain?

I see mostly sporadic discharge events, with 1ns durations. They must be
a pretty localized processes. Whether the avalanche needs any help from
new thermal carriers is not so important, however the current, if at all
localized, represents a rather high current density. The avalanche
process is reminesent of gas discharge physics, hence the plasma.

> Motorola's reference to "microplasma theory" is just two words in the
> 1980 Motorola Zener Diode catalogue, to which I too have access. Your
> "mesoplasma" is worked out in more detail, but strikes me as an
> unnecessary.

I'm not sure you should so glibly dismiss their reference. In truth, I
very much liked the mesoplasma idea when it occurred to me, thinking
first about silicon suppressors and then about the simularity to
radioactive-decay detector traces, which are single-triggered events.
Anyway, that's what the scope traces seem to be showing. Even my simple
physics seemed plausible and Motorola's reference to a microplasma theory
sounds worth examining. Why are you so skeptical of the idea of a very
small number of active sites? Think of the dislocations and impurity
centers which could be responsible for that.

> To explain the low current behaviour you and Tony and Jeroene Belleman
> has seen, you need only invoke the idea, clearly expressed in the
> literature on "Geiger mode" single photon avalanche diodes (SPADs),
> that a sufficiently low avalanche current self-extinguishes due to
> statistical fluctuations in the number of holes generated. If you
> assume that at 100uA current is transferred through a junction with
> a 1psec propagation delay, some five holes have to generate
> hole-electron pairs on the negative side of the junction every
> picosecond. Roughly once every 150psec, none of them will make it,
> and the avalanche will be extinguished.

Aside from my discomfort with your 1ps timescale, these numbers just
don't add up as an explanation for my observations. I see as many as
220,000,000 electrons in a single 1.0ns event, whereas your 100uA for
150ps provides less than 100,000 electrons. You'd need to invoke over
2000 of your SPAD processes, synchronized during the 1000ps interval, and
then waiting for about 85,000ps before synchronously starting again.

> The current from your bias resistor then charges up the diode

> capacitance (and any other capacitance that is handy) until thermal


> excitation produces a charge carrier.

Fine, exactly what we already said wrt charging the capacitance, however,
it appears to me the probability of a new event is much more related to
the voltage level, than to the time duration. Hence the concept of a
noisy threshold. Also, surely plenty of thermal carriers are around
already.

> This current then discharges the capacitance, reducing the voltage
> across the junction to give us Tony's exponential decay, until the
> current is low enough to spontaneously self-extinguish.

Sure the current discharges the capacitance, as I calculated, however,
except for very high parallel capacitances, it's not a "decay" and it
isn't exponential. Instead it's a relatively steady discharge current,
e.g. with 1000pF in parallel, 4.3mA lasting for 26ns. Furthermore, it
stops suddenly after the voltage has ramped down to a lower level, while
the current is still at full strength.

>>>
>>> /| 1N5245B at 50uA
>>> 200mV FS / |
>>> /| / | /|
>>> /| / | /| / | /| / | /|
>>> / | /| / | / | / | /| / | / |/ | /| _____
>>> | / |/ | /| / |/| / |/ | / |/ | / |/ |
>>> |/ | / |/ |/|/ |/ | /|/ |
>>> |/ |/ |
>>> /
>>> scope trace, continuous events, 10us FS 14.41 V
>>> average value

I'll admit the steady, repeatable, rather-high current and its sudden
cessation do puzzle me and I'm sure it's an important clue which must be
explained. This may be the observation which requires the use of both
holes and electrons, to get a very high M.

> As the DC current rises, the time required for the avalanche to
> self-extinguish rises quite rapidly - giving the intermittent voltage
> spikes seen by Win from 50uA to 75uA and the "rare" spikes seen out to
> 200uA.

No Bill, it's quite different. At higher average currents, a "steady"
current flows at the _lower_ voltage level, so apparently the voltage
isn't high enough to initiate one of these microplasma avalanches we've
been examining (perhaps a series of very small events? - but not at all
like the microplasma discharges). Then something seems to happen and the
slightly noisy steady current stops, allowing the voltage to rise and
whammo!

> Simple, and just two assumptions - the self-extinguishing avalanche
> with a 1psec wide junction, and some 460,000 avalanche sites to divide
> the 100uA leakage current into the 0.2pA per site required to explain
> 13.5+/-1.5 avalanche initiations every 10usec.

Nice attempt, but needs more work!

slo...@sci.kun.nl

unread,
Aug 5, 1997, 3:00:00 AM8/5/97
to Winfield Hill

In article <5s6f90$9...@fridge-nf0.shore.net>,

hi...@rowland.org (Winfield Hill) wrote:
>
> slo...@sci.kun.nl, <slo...@sci.kun.nl> said...
> >
> >In article <5s2t2c$2...@fridge-nf0.shore.net>,
> > hi...@rowland.org (Winfield Hill) wrote:

<snip>

> > To explain the low current behaviour you and Tony and Jeroene Belleman
> > has seen, you need only invoke the idea, clearly expressed in the
> > literature on "Geiger mode" single photon avalanche diodes (SPADs),
> > that a sufficiently low avalanche current self-extinguishes due to
> > statistical fluctuations in the number of holes generated. If you
> > assume that at 100uA current is transferred through a junction with
> > a 1psec propagation delay, some five holes have to generate
> > hole-electron pairs on the negative side of the junction every
> > picosecond. Roughly once every 150psec, none of them will make it,
> > and the avalanche will be extinguished.
>
> Aside from my discomfort with your 1ps timescale, these numbers just
> don't add up as an explanation for my observations. I see as many as
> 220,000,000 electrons in a single 1.0ns event, whereas your 100uA for
> 150ps provides less than 100,000 electrons. You'd need to invoke over
> 2000 of your SPAD processes, synchronized during the 1000ps interval, and
> then waiting for about 85,000ps before synchronously starting again.

You want 220 million electrons in 1nsec? I can adjust the model to fit. I
don't believe you can go from nothing to 35mA and back again in 1nsec, so
I don't have to believe the numbers I get, but a 35mA current travelling
across a 3.3fsec wide junction would self-extinguish after about 1nsec.

Probability that a hole generates an electron when crossing the junction
of 0.992, number of holes crossing a 3.3fsec junction 726, 0.992^726
equals 0.3%, so an even chance of no electrons every nanosecond. Very
crude model, but it captures the basic idea.

The numbers for Tony's discharges exponentially decay from 260uA to about
50uA over an appreciable fraction of a microsecond and then die, are much
more believeable.

Your nanosecond spikes have got to involve some inductance.

>
> > The current from your bias resistor then charges up the diode
> > capacitance (and any other capacitance that is handy) until thermal
> > excitation produces a charge carrier.
>
> Fine, exactly what we already said wrt charging the capacitance, however,
> it appears to me the probability of a new event is much more related to
> the voltage level, than to the time duration. Hence the concept of a
> noisy threshold. Also, surely plenty of thermal carriers are around
> already.

The published leakage currents - 100nA/200nA for your diode and Tony's
respectively - are way high compared with the few hundred nanoseconds you
wait before an avalanche restarts, but note that the thermal charge
carrier has to generate its electron close to the cathode if the electron
is going generate its full complement of 125 holes before hitting the
anode to get an even chance of starting an avalanche. As the voltage
across the junction rises, the targe area gets bigger as the avalanche
gain increases.

And of course, we can invoke a lot of parallel avalanche sites, and divide
the leakage current over the lot of them, while assuming that at low
currents we are only looking at one.


> > This current then discharges the capacitance, reducing the voltage
> > across the junction to give us Tony's exponential decay, until the
> > current is low enough to spontaneously self-extinguish.
>
> Sure the current discharges the capacitance, as I calculated, however,
> except for very high parallel capacitances, it's not a "decay" and it
> isn't exponential. Instead it's a relatively steady discharge current,
> e.g. with 1000pF in parallel, 4.3mA lasting for 26ns. Furthermore, it
> stops suddenly after the voltage has ramped down to a lower level, while
> the current is still at full strength.

This is markedly different from Tony's exponential decay, and sounds more
like an LC ring killed when the current hits zero.

I see it exactly the other way around. The "steady" current is low enough
that there is a finite change that the avalanche will self-extinguish;
when this happens the current into the junction charges the diode
capacitance until the avalanche re-initiates, discharges the capacitance
and recovers to the quasi-stable "steady" current that persists until the
statistical fluctuation in avalanche current hits zero.

> Nice attempt, but needs more work!

It looks like I'll have to write my own AoE before I can get the idea
across ...

Roy McCammon

unread,
Aug 5, 1997, 3:00:00 AM8/5/97
to Winfield Hill

Winfield Hill wrote:

> Spike period and statistics. The event-discharge time intervals are
> quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
> min/max). Observing with a 10us window, I _always_ count from 12 to
> 15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
> the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.
> This is more like a relaxation oscillator with a noisy threshold and
> a noisy discharge step, and less like a chaotic or random process.

This is pure speculation based on some of the chaos
theory that I have read.

Some chaotic process exhibit a bifrucation of states as
a function of some parameters. I wonder if either you or
Tony has seen this. I think it might manifest itself by
showing no oscilation at low current (I think that has
already been established). Then as currnet is increased,
you reach a two state one period oscilation. Increase
the current more and and you might see a 4 state oscilation
with two periods. Keep increasing the current and see more
states and more periods. I'm fishing here. Did anything
like that show up?

Opinions expressed herein are my own and may not represent those of my employer.


Roy McCammon

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Aug 5, 1997, 3:00:00 AM8/5/97
to Bill Sloman

Bill Sloman wrote:

> In article <33E6D3...@Today.Thanks>, Mike <NoS...@Today.Thanks> says:

> >I think everyone got lost on the original post. Who made it?
>
> I think I have that dubious honour.


I'd have to say that it is the best
thread this year.

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
to

Winfield Hill at hi...@rowland.org says...
>
>Bill Sloman, <slo...@sci.kun.nl> said...
>>
>> R.J.McIntyre "Theory of microplasma instability in silicon" J.Appl.Phys.
>> volume 32 pages 983-95 (1961) looks promising. Sadly, our library
>> only goes back to 1968. Posts from readers with older libraries might
>> tell me whether it is worth ordering this from the inter-library
>> loan service.

OK, I got it, but it's not so interesting, heavy into statistical theory
aimed at determining if a microplasma stops because the number of carriers
randomly fluctuates to zero, even for graded or step junctions (he claims
that it does).

> I'm on the trail of a series of articles by a bunch of fellas: McKay, Rose,
> Senitskz, Moll, Miller, Goetzberger, Stepehns, Haitz, Cynoweth and Wolff.
> All in the late 50's and early 60's. Fortunately our library ...

Yeasssss!!! Here, buried in our library's stacks, I found the real mother
lode: A dozen papers, reporting electron multiplication and avalanche
breakdown studies, starting in 1953 and extending for 10 years [I lose the
trail in 1961; a citation search by our librarian should pick it up again].

After scanning the papers, I'm too excited about what I read not to report it
briefly. They're mostly in Physical Review, but a few of the later ones are
in Journal of Applied Physics (JAP).

Bill, these papers totally support and flesh out both the microplasma theory
and the large-M breakdown mechanisms - just as I've been suggesting that you
consider more seriously. They also include extinguishment aspects similar to
some of the mechanisms in the IMPATT and SPAD diodes you've mentioned, but
perhaps with somewhat different time scales.

First, we have K.G. McKay and K.B. McAfee in 1953 (91, 1079), and continuing
with McKay in 1954 (94, 877). Their junction evidentally had a small number
of lower-voltage sites, and breakdown would commence with a single site
running at its full current (say 50uA), with 0.5 to 2us "pulse-width
modulation" durations. After increasing the total junction current to over
50uA, this site would be on continously, and a new site would start, say at
32uA. And etc.

Also in 1954, P.A. Wolff (95, 1415) writes a theory paper and says that the
mean-free path for electron-phonon interaction is 200A, but for ionizing
electric-field strengths (6x10^5 V/cm), it drops to 15A for electron-hole
pair production. This helps set the stage for very small plasma sizes.

Then in 1956 come A.G. Chynoweth and K.G. McKay "Photon Emission from
Avalache Breakdown in Silicon" (102, 369), who say the microplasmas are a few
hundred A in diameter and occur at many separate places, and that these
microplasmas also emit light (!), probably when energetic electron-hole pairs
recombine. The emitted photons had between 1.9 and 3.1 ev of energy, peaking
at 2.2 ev, and occurred at a low rate relative to the electron current.
(Light emission was first reported in 1955, but not localized.)

Incidentally, Chynoweth and McKay are the first I see in the literature using
the term "microplasma" and they don't reference it to someone else.

Then we have D.J. Rose "Microplasmas in Silicon" (105, 413) in 1957 who
suggests chance-fluctuation current decreases for terminating a microplasma.
He uses a 500A microplasma size, and estimates a 36C temperature rise in the
microplasmas, which he uses to argue for a slightly reduced ionization
coefficient and a failure to simply reignite. He estimates both transit
times and thermal time constants of about 0.1ns.

In 1958, we have B. Senitzky and J.. Moll (110, 612) who fully confirm that
junctions break down in tiny spots and also call these spots microplasmas.
They measured values of M from 140 to 400, dropping as the microplasma
saturated at say 100uA. They also estimated a lower temperature increase in
the microplasma of 1.2x10^5 C/amp.

In 1960, there's a massive two-paper set by Batdorf, A.G. Chenoweth and
others in JAP. (31, 1153). They credit Rose with the name, "microplasma" and
they concentrated on attempting to achieve breakdown without microplasmas at
all, but "macroplasmas" instead. They were partially successful, although
the breakdowns were slightly concentrated and tended to become more so at
higher currents, i.e. microplasmas after all.

One interesting Senitzky and Moll finding (reported by Batdorf) was that a
microplasma originating at an inhomogeneity would carry higher breakdown
currents by an expansion of the breakdown area, rather than by the formation
of additional breakdown sites. BTW, this could be exactly what's happening
in my own test diode. In this way a single "event" can carry far more than
0.1mA. This probably isn't happening in the quiet 15V zener diode I rejected
for testing. Of course, another possibility is that my part's microplasmas
are say 5mA rather than 0.1mA each. This I'd like to examine further.

Finally, in 1963 we have Haitz et.al. "Localized Photomultiplication Studies
on Microplasmas" (JAP. 34, 1581), who also worked to achieve silicon
junctions with very hard (i.e. sharp) breakdowns. They also made specific
measurements of the factor M inside a microplasma, and saw as high as 10^6.
However, when switched on, generally a single microplasma had a "fixed
current". They used plots of 1/M vs voltage, which are straight lines
heading toward 1/M = 0 or M -> infinity. They showed that M has a very high
voltage coefficient, e.g. M=100 at 31.32V doubling to 200 at 80mV higher.
They found single bright microplasmas in some crystals, which they attributed
to surface defects, but in others they were smaller and grouped together.

In conclusion, I'm delighted to have this pile of papers in front of me.
This is especially so, given Bill Sloman's skepticism about the step sizes I
reported, and of any necessity or value in invoking microplasmas as a
mechanism, plus his scorn for Motorola's "two-word comment" as a useful
reference. I agree that some of Bill's knowledge and intuition is borne out
by these papers, but much of what I suggested and he discounted, is seen to
be fully accepted by these researchers.

--
Winfield Hill hi...@rowland.org
Rowland Institute for Science
Cambridge, MA 02142


Tony Williams

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Aug 5, 1997, 3:00:00 AM8/5/97
to

In article <5s7bb3$n...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:
[snip]
>
> We do have a very fast single-shot scope at the Institute. Sheesh, this is
> turning into a real project.

Did we ever get a Job Number that we can book all this time to?

Winfield Hill

unread,
Aug 5, 1997, 3:00:00 AM8/5/97
to

slo...@sci.kun.nl at slo...@sci.kun.nl says...

>
> hi...@rowland.org (Winfield Hill) wrote:
>>
>> Aside from my discomfort with your 1ps timescale, these numbers just
>> don't add up as an explanation for my observations. I see as many as
>> 220,000,000 electrons in a single 1.0ns event, whereas your 100uA for
>> 150ps provides less than 100,000 electrons. ...

>
> You want 220 million electrons in 1nsec? I can adjust the model to fit. I
> don't believe you can go from nothing to 35mA and back again in 1nsec,...

Let me get this straight. You simply don't believe my measurements?
Perhaps, since q = CV, you prefer to think the capacitance of the diode
has suddenly changed?

> Your nanosecond spikes have got to involve some inductance.

You imply I wouldn't take proper care? I'd estimate it's under 2nH, which
corresponds to less than 24mV for 12 mA/ns. Whereas I saw more than -200mV
steps at the 12mA current level. And etc. Since the inductive voltgae-step
component is a small fraction of the total step, this is why my waveforms
basically show no substantial inductive or ringing effects.

> ... As the voltage across the junction rises, the targe area gets bigger


> as the avalanche gain increases.

Let's see, so now you do begin to admit to gains of M>>1.0 in our diodes?

>>> This current then discharges the capacitance, reducing the voltage
>>> across the junction to give us Tony's exponential decay, until the
>>> current is low enough to spontaneously self-extinguish.
>>
>> Sure the current discharges the capacitance, as I calculated, however,
>> except for very high parallel capacitances, it's not a "decay" and it
>> isn't exponential. Instead it's a relatively steady discharge current,
>> e.g. with 1000pF in parallel, 4.3mA lasting for 26ns. Furthermore, it
>> stops suddenly after the voltage has ramped down to a lower level, while
>> the current is still at full strength.
>
> This is markedly different from Tony's exponential decay, and sounds more
> like an LC ring killed when the current hits zero.

It would be more pleasant if you'd stop simply denying what I see and report.
First, we know these diodes vary dramatically from part to part, but we also
know to understand the physics, and feel comfortable predicting zener use in
designs, etc., it's necessary to explain observations. Bill, I'm not seeing
an LC ring, and obviously would have seen and stated if so. Anyway, how
would it get suddenly damped if I was? Possibly such a thing could happen
once under the right conditions (current injected the other way, but from
where?) however my measurements were consistant across the thousands of
discharges I observed.

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
to

Bill Sloman, <slo...@sci.kun.nl> said...

>
>In article <33E6D3...@Today.Thanks>, Mike <NoS...@Today.Thanks> says:
>>
>> When I left this discussion, the claim was oscillations in the VHF-UHF
>> range. Now, the best you can come up with is surface contamination noise
>> in the microamp region - slightly above DC!
>
> I think Win, Tony and Jeroen Belleman are all seeing stuff around 1MHz.
> The falling edges, corresponding to avalanche initiation are uniformly
> faster than their scopes can follow, ...

All my early measurements were with a 2.7ns probe system. Hey, that's much
faster than 1MHz.

As you can see from one of my posts early this AM to Tony, I raised the
ante with my elegant Tektronix 1GHz 1pF FET probe, which showed 1.0ns
negative discharges for my subject diode, without any extra capacitance.
[The spiking ramp slowed to about 26ns with an extra 1000pF in parallel.]
Although careful measurements with the same setup, at the same time, shows
0.7ns probe-plus-scope response time, I had to take the 1.0ns measurements
with the digital scope sampling in "equivalent-time" sampling mode. With
this mode turned off, I could see that the digitized individual spikes were
rather similar for the trigger setting I was using, yet the use of multiple
erratic spikes to build up a detailed waveshape and time was unsettling.
So it's possible my diode was actually spiking at faster than 1.0ns.

We do have a very fast single-shot scope at the Institute. Sheesh, this is
turning into a real project.

>> I think everyone got lost on the original post. Who made it?


>
> I think I have that dubious honour.

What was the original topic?

Also, who is Mike <NoS...@Today.Thanks> anyway? I didn't see his post.

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
to

Bill Sloman, <slo...@sci.kun.nl> said...
>
> <giant snip>

>
>> Too bad they don't pass along any
>> references to the "microplasma discharge" theory!
>
> R.J.McIntyre "Theory of microplasma instability in silicon" J.Appl.Phys.
> volune 32 pages 983-95 (1961) looks promising. Sadly, our library

> only goes back to 1968. Posts from readers with older libraries might
> tell me whether it is worth ordering this from the inter-library
> loan service.

I'm on the trail of a series of articles by a bunch of fellas: McKay, Rose,

Senitskz, Moll, Miller, Goetzberger, Stepehns, Haitz, Cynoweth and Wolff.

All in the late 50's and early 60's. Fortunately our library goes back
that far so I should be able to find them, or I'll walk over to MIT's
Barker Engineering library (if I can find the time). I found my references
by following a remark by Giacoletto at MSU, who did some of the early work
in minority-carrier lifetimes and surface effects in junction devices in
the mid 50's.

Anyway, thanks Bill for the extra reference; McIntyre wasn't mentioned.
How'd you come across it?

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
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Roy McCammon at rbmcc...@mmm.com says...

>
>Winfield Hill wrote:
>
>> Spike period and statistics. The event-discharge time intervals are
>> quite regular for my diode, typically from 0.4 to 1.0us (0.2 to 1.5us
>> min/max). Observing with a 10us window, I _always_ count from 12 to
>> 15 events. This is 13.5 +/= 1.5 events/10us and is not at all like
>> the 13.5 +/- 7.2 (two sigma) we'd expect from random statistics.
>> This is more like a relaxation oscillator with a noisy threshold and
>> a noisy discharge step, and less like a chaotic or random process.
>
> This is pure speculation based on some of the chaos
> theory that I have read.

I certainly think the process has chaotic elements, but I was trying
to point out a surprising degree of regularity as well.

> Some chaotic process exhibit a bifrucation of states as
> a function of some parameters. I wonder if either you or
> Tony has seen this.

Yes, there do seem to be different modes of operation, sometimes
seen occuring together, perhaps in different parts of the junction,
but in parallel. It seems clear there are multiple small sites.
Hmmm, it would be highly speculative to try to classify the events,
identify the guilty parties and then characterize each.

Winfield Hill

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Aug 5, 1997, 3:00:00 AM8/5/97
to

Tony Williams at to...@ledelec.demon.co.uk says...
>
> [Win]
>> Ahh, great! That would imply a discharge current of 10 to 20mA - in

>> the same ballpark as the 6mA I estimated for 10ns. If my discharge was
>> really in 3 to 5 ns, we actually have matching event-size observations.
>
> I am unhappy with that 6mA and 20mA, especially your derivation of I
> by simply calculating Vzener/500ohms. I don't think the microavalanches
> are aiming towards 0v at all.

I'm not sure what you mean here, but my discharges do have a constant,
rather than exponential slope (except for 0.1uF). In that sense they're
headed for 0V. Then they suddenly stop.

> I don't have a current probe, but stuck a 2-ohm resistor in series
> with the 0v end of the cap. 1mA Ipk would produce 2mV, which I should
> be able to see on the scope at 5mv/div. There was nothing visible.
>
> -----+ +----- +50uA
> | |
> | | _____-50uA This is the current through a 100R
> | / in series with 9400pF. It confirms
> | / the estimate of 250uA.
> | /
> | /
> |/_____________ -200/-300uA, mostly -280uA.

Very interesting. Do I see a dropping current, but the suddenly a complete
cessation. Aha.

Hey Tony, I like the idea of a sense resistor - I'll try that too.

What do you see with no capacitor at all? Anything like mine? Or instead,
maybe a step ON and then later OFF?

> (Note, this current waveform gives me a problem. I can clearly
> see a charging current of +50uA in the cap. But I have "proved"
> above that it should be about 11uA less than that. Hmm, looking at
> Ipk = -280 v Imin= -50uA suggests I should redo the RC or 2RC estimate.)

After taking measurements with my nice Tek scope and probe combo, I'm
convinced that for my noisy test diode, _all_ the current comes from these
microplasmas.

>-------------------------------------------------------------------------
>
>>> This last mode of osc is quite aggressive, it has the capability to
>>> kick a 10uF capacitor and is my reason for a new doubt about the
>>> traditional advice of "stick a 0.1 across it".
>>
>> Interesting. Just how big is the 10uF kick? Maybe the microplasm
>> discharge can be much more energetic if a bigger capacitor is available
>> to continue forcing the higher voltage while supplying much more energy.
>>
>
> Ok, Results are:- 10uF/134uA, 3 to 5mV pk-pk. 2u2/154uA, 5 to 9mV pk-pk.

Yes indeed. More energy in the discharge with bigger capacitors.

>-------------------------------------------------------------------------
>
>> ... I think at the low current we're considering, we really are seeing a


>> crude type of relaxation oscillator with perhaps only a few active sites
>> involved. In these devices, when the current charges the voltage above
>> some slightly noisy threshold (varying no more than 50mV in my case), a
>> microplasma discharge avalanche is triggered, discharging a somewhat
>> indeterminant amount of charge before stopping. Then the process starts
>> all over - just like a relaxation oscillator. See below.
>
> I believe that your observation is correct. Carefully watching waveforms,
> suggests that your 10/12 discharge-sites is not far off for 0pF, reducing
> to 4 to 6 sites for 4700pF. Best guesses only.
>-------------------------------------------------------------------------
>
>> Tony, I find this all very interesting. I'm surprised more isn't said
>> about it in the literature and also that I didn't think of checking it
>> before myself. Thanks much.
>
> It *is* interesting, and so easy to do. I suspect that it is
> well documented somewhere though. Perhaps that fact that it
> appears to be so unpredictable as to have no application is the
> reason for having little in the literature.

Well, hey hey Tony! I did find a pile of literature done well before our
time, over 35 years ago, when some other smart folks still thought this was
interesting. Looks like many folks spent years on it. See my next post.

Bill Sloman

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Aug 5, 1997, 3:00:00 AM8/5/97
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In article <33E6D3...@Today.Thanks>, Mike <NoS...@Today.Thanks> says:
>
>Winfield Hill wrote:
>>
>> slo...@sci.kun.nl, <slo...@sci.kun.nl> said...
>> >
>> >In article <5ru8qo$2...@fridge-nf0.shore.net>,

>> > hi...@rowland.org (Winfield Hill) wrote:
>> >>
>> >> Bill Sloman, <slo...@sci.kun.nl> said...
>> >>-> [snip]
>
>When I left this discussion, the claim was oscillations in the VHF-UHF
>range.
>
>Now, the best you can come up with is surface contamination noise in the
>microamp region - slightly above DC!

I think Win, Tony and Jeroen Belleman are all seeing stuff around 1MHz.
The falling edges, corresponding to avalanche initiation are uniformly

faster than their scopes can follow, so there may be components in the
100-200MHz range that my informants claimed to have seen back around 1970.
One of the comments made by my informants was that they had to borrow
a really fast scope to see the oscillation.

If you think surface contamination noise can explain what is being
reported, you have to explain the variation with diode current, and
the variation with extra capacitance hung across the diode.

I'm sure that for master of Spice this will be a trivial exercise. I
shall look forward to your simulations this afternoon (Dutch time -
later this morning - US time).

<snipped apology to Win, who seems to be having a whale of a time>

>I think everyone got lost on the original post. Who made it?

I think I have that dubious honour.

Bill Sloman (slo...@sci.kun.nl) | Precision analog design
TZ/Electronics, Science Faculty, | Fast analog design and layout
Nijmegen University, The Netherlands | Very fast digital design/layout
| e-mail for rates and conditions.

Bill Sloman

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Aug 5, 1997, 3:00:00 AM8/5/97
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<giant snip>

> Too bad they don't pass along any
> references to the "microplasma discharge" theory!

R.J.McIntyre "Theory of microplasma instability in silicon" J.Appl.Phys.


volune 32 pages 983-95 (1961) looks promising. Sadly, our library
only goes back to 1968. Posts from readers with older libraries might
tell me whether it is worth ordering this from the inter-library
loan service.

Winfield Hill

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Aug 6, 1997, 3:00:00 AM8/6/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...
>
> Winfield Hill <hi...@rowland.org> wrote:
>[snip]

>> Sheesh, this is turning into a real project.
>
> Did we ever get a Job Number that we can book all this time to?

Yes, we did. The number is 42.

-- Win


Tony Williams

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Aug 6, 1997, 3:00:00 AM8/6/97
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In article <5s8490$h...@fridge-nf0.shore.net>, Winfield Hill

<URL:mailto:hi...@rowland.org> wrote:
>
> Tony Williams at to...@ledelec.demon.co.uk says...

> > I am unhappy with that 6mA and 20mA, especially your derivation of I


> > by simply calculating Vzener/500ohms. I don't think the microavalanches
> > are aiming towards 0v at all.
>

> I'm not sure what you mean here, but my discharges do have a constant,
> rather than exponential slope (except for 0.1uF). In that sense they're
> headed for 0V. Then they suddenly stop.

I am beginning to suspect that your 0.5W 15v diode is quite different
to my 400mW 10/12v diodes. Looking at my total stock I do see quite
a variation in the discharge "resistance" (for want of a better word).
I suggest that any speculation on the discharge-mechanism should
include the possibility of something that allows for this variation.

>
> > I don't have a current probe, but stuck a 2-ohm resistor in series
> > with the 0v end of the cap. 1mA Ipk would produce 2mV, which I should
> > be able to see on the scope at 5mv/div. There was nothing visible.
> >
> > -----+ +----- +50uA
> > | |
> > | | _____-50uA This is the current through a 100R
> > | / in series with 9400pF. It confirms
> > | / the estimate of 250uA.
> > | /
> > | /
> > |/_____________ -200/-300uA, mostly -280uA.
>

> Very interesting. Do I see a dropping current, but the suddenly a complete
> cessation. Aha.

Yes, I do see the discharge switch-off whilst a finite current still flows.


> Hey Tony, I like the idea of a sense resistor - I'll try that too.

Don't forget that you must use a current-shunt whose value is small
compared with the discharge "resistance" in the die, otherwise you
seriously alter the experimental conditions. This may be a problem
with your particular 15v dut, with it's fast discharging and is
the reason I suggested a current probe in another post.

>
> What do you see with no capacitor at all? Anything like mine? Or instead,
> maybe a step ON and then later OFF?

Similar to your descriptions but it's pushing my 20meg scope and
I do not wish to report any results from that.

>
> > (Note, this current waveform gives me a problem. I can clearly
> > see a charging current of +50uA in the cap. But I have "proved"
> > above that it should be about 11uA less than that. Hmm, looking at
> > Ipk = -280 v Imin= -50uA suggests I should redo the RC or 2RC estimate.)
>

> After taking measurements with my nice Tek scope and probe combo, I'm
> convinced that for my noisy test diode, _all_ the current comes from these
> microplasmas.

Agreed, in a separate post that crossed with this one.

However, this is a relevant place to return to that photosensitivity
question. I have previously reported that shining a torch beam onto
the zener drastically reduces the size of the oscillations. Silly me,
the answer is obvious now.... shining the torch beam onto the zener
simply causes it to generate a photocurrent that drains off some of
the 50uA stimulus (sideways) and the operating point of the relaxation
osc just moves downwards under a reduced stimulus. In fact, you can get
an estimate of the photocurrent by pushing the stimulus back up until
it returns to the original picture.

(My measuring diodes are now wrapped in foil to avoid day by
day variations).

[output with big shunt-C]

> > Ok, Results are:- 10uF/134uA, 3 to 5mV pk-pk. 2u2/154uA, 5 to 9mV pk-pk.
>

> Yes indeed. More energy in the discharge with bigger capacitors.

Just a remark here. I am reasonably happy that external shunt-C up
to about 10nF will not materially affect the avalanching mechanism that
is seen just on the diode itself. But the joules required to kick larger
values of external C may distort the experiment.

> Well, hey hey Tony! I did find a pile of literature done well before our
> time, over 35 years ago, when some other smart folks still thought this was
> interesting. Looks like many folks spent years on it. See my next post.

I saw it. Got any sleeping pills in stock? :-)

Kenneth R. Burch

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Aug 6, 1997, 3:00:00 AM8/6/97
to

From an oscillator circuit perspective, here are some additional references that
might be of some interest.


Clement and Starliper describe an obscure circuit containing 5 diodes (and no
other components). One of these is a zener diode. They state that the circuit
is a relaxation oscillator with an output that is a string of small amplitude
pulses at a rate of approximately 40 kHz.

R. D. Clement and R. L. Starliper, "Relaxation Oscillators - Old and New",
Electronics World, may 1971, pp36-37.


Older references include an L/C circuit which uses a Zincite crystal diode
and dates back to 1924.

Edwid F. Ehlinger, "The Modern Solid-State Oscillator", QST, September 1971,
p49.

This article references "The Crystodyne Principle", Radio News, 1924., which
credits the circuit to O. V. Lossev, a Russian inventor.

"The Crystodyne Principal", Radio News, Vol. 6, No. 3, September 1924, pp294-295.


Other related papers of the time include

I. Podliasky, "Crystodyne Receivers and Amplifiers", Radio News, Vol. 6, No. 4,
October 1924, pp470,540,542.

J. E. Anderson, "Vacuum Tube Oscillators Record Distant Earthquakes", Radio News,
Vol. 6, No. 5, November 1924, pp660-662,831-832.

Greenleaf W. Pickard, "The Discovery of the Oscillating Crystal", Radio News,
Vol. 6, No. 7, January 1925, pp1166,1270.

O. V. Lossev, "Oscillating Crystals", Radio News, Vol. 6, No. 7, January 1925,
pp1167,1287-1291.

J. Piesch, "The "Singing" Crystal", Radio News, Vol. 8, No. 7, January 1927,
pp788-789,903-905.

Tony Williams

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Aug 6, 1997, 3:00:00 AM8/6/97
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In article <5sac5j$l...@fridge-nf0.shore.net>, Winfield Hill

<URL:mailto:hi...@rowland.org> wrote:
>
> Tony Williams at to...@ledelec.demon.co.uk says...

> > In fact, the "dc-current" that any ammeter sees, say at 50uA, is actually
> > an integrated version of the succesive cap charge/discharges. It puts a
> > nice little twist on what precisely causes the shape of the knee of a zener.
>
> That's an astute observation. What "Joe Engineer" should take away from
> this thread is the fact that modest zener currents are often made up of
> pulse-width averages of discrete current levels, crudely speaking.

Well, the smooth curve of a zener knee is what started this
particular thread. We all think (thought!) 'leakage' caused it.

That reminds me, I've been meaning to do a VI characteristic
with the zener well slugged versus allowing it to osc. Just
out of curiousity. Must do that sometime.

> > I don't know Win, these tens of mA bother me. You are not actually
> > seeing them, you are deriving them from timing measurements off
> > a relaxation oscillator.

> > ... I am uneasy about the L/C ratio around your 60pF circuit. ...
> > I distrust that 60pF column, it may be being distorted by some L.

> Bill also raised this issue (hah! getting me a bit steamed up).
> I was very careful Tony, and there's no LC effect in my test setup.
>
> However, I've got to do more investigation into these 1ns events.
> What are they all about. Very surprising and disturbing, but quite real.

Confession time. When I re-looked at my total stock yesterday I
realised that some of the edges seen were really being limited by
the slew-rate of my scope. Just on a few of the higher-voltage
diodes. Posts were crossing each other and the very fast edges
that were reported in the documentation of the 50's/60's suggested
that the extreme current spikes you were reporting were almost
certainly correct. So I was beginning to be converted to the
high current pre-spikes, but put this post up anyway.

I believe the mA of current-spike you are calculating from
the dV/dT you see across the capacitance and believe you will
confirm the 4.3mA with the 2R shunt in series with the 1000pF.

In fact I am even prepared to speculate even further......

We are talking of the 50's and 60's. Early researchers would have
had a scope like mine (20meg) and probably would have got similar
results to mine. Someone has been mentioned in those papers, can't
remember, who appears to have had something much faster and was
able to show faster edges, but only of 100uA amplitude I think.

The bell that is going off in my hindbrain is signalling the
possibility that, in the intervening 35+ years, no one has looked
at these things with a scope as fast as you have today. Have you
considered the possibility that these mA of discharge-current have
always been there, just waiting for someone with a fast enough
scope to see and investigate?

Am I being fanciful here? Did scopes with <1nS risetime exist
in the 60's or not? I've forgotten what the 555 could do.


[big snip]

> > Well, what I see up in Mode.4 is spikes ( or clusters of) which
> > are separated by relatively long periods at the lower discharge
> > voltage. If you expand one of those spikes, each appears to be
> > just one charge and discharge of the relaxation osc, with a
> > dwell time in between. We still have the stimulus flowing, so
> > what on earth stops it from recharging the cap immediately?
>
> I assume you're referring to a voltage waveform something like this,
> from my earlier post (no parallel capacitor):


>
> ,| | |, | , ___+150mV
> |||| ||: || |
> |||| |, |||| ||:||
> ,._,.-,-_.,I||I,-.I|L|,_.-,_,._,.-||II,._,.-,-I||II|, __ 0mV
>
> scope trace at 100uA, scattered events (5us/div)
>

> Ahh, yes, we do seem to have a nice steady current flowing between the spike
> events, which is a little to high for one fully-saturated microplasma, and
> must be some type of quiet mode of several microplasmas working together....
>
> When the spiking starts, it's just the regular stuff we had before the
> steadiness.
>
> As to what starts this, Bill suggests it's the same process which all the
> researchers seem to agree upon for stopping a microplasma (that ending step
> you see). The steady current, which is a low near-starving level for
> maintaining high M in the microplasma, randomly stops for a very small
> fraction of a ns, afterwhich the microplasma remains off. A modest raised
> temperature of a microplasma channel (if not too high) can help provide a
> basis for it not to immediately restart, staying off long enough for all
> the nearby carriers, previously helping sustain the current flow, to be
> swept away during one of these hesitations.
>
> The thing that puzzles me is the apparent stability of the quiet flow.
> Convinced now of the dominance of the microplasmas, and their high M, which
> increases the current flow until each microplasma saturates, how can we have
> these steady currents, which don't appear to exactly represent the summation
> of fully-switched ON microplasmas? The answer could involve a very rapid
> switching of these currents inside the junction with its capacitance, and
> not apparent at the terminals. If I remember correctly, one of the papers
> pointed out that when two microplasmas are running at the same time, one
> switching on can influence the other to switch off, possibly by dipping the
> local voltage slightly, etc. ...

I think this Mode.4 characteristic has to wait until the exact
mechanism of the 'normal' relaxation oscillator is determined.
It is almost certainly derivation of that, possibly with some
joules factored into the avalanche site.

Winfield Hill

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Aug 6, 1997, 3:00:00 AM8/6/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...

>
> Winfield Hill <URL:mailto:hi...@rowland.org> wrote:
>>
>> Tony Williams at to...@ledelec.demon.co.uk says...
>>>
>>> I am unhappy with that 6mA and 20mA, especially your derivation of I
>>> by simply calculating Vzener/500ohms. I don't think the microavalanches
>>> are aiming towards 0v at all.
>>
>> I'm not sure what you mean here, but my discharges do have a constant,
>> rather than exponential slope (except for 0.1uF). In that sense they're
>> headed for 0V. Then they suddenly stop.
>
> I am beginning to suspect that your 0.5W 15v diode is quite different
> to my 400mW 10/12v diodes. Looking at my total stock I do see quite
> a variation in the discharge "resistance" (for want of a better word).
> I suggest that any speculation on the discharge-mechanism should
> include the possibility of something that allows for this variation.

That's an excellent suggestion. Yes, our parts do seem quite different.

>>> I don't have a current probe, but stuck a 2-ohm resistor in series
>>> with the 0v end of the cap. 1mA Ipk would produce 2mV, which I should
>>> be able to see on the scope at 5mv/div. There was nothing visible.
>>>
>>> -----+ +----- +50uA
>>> | |
>>> | | _____-50uA This is the current through a 100R
>>> | / in series with 9400pF. It confirms
>>> | / the estimate of 250uA.
>>> | /
>>> | /
>>> |/_____________ -200/-300uA, mostly -280uA.
>>

>> Very interesting. Do I see a dropping current, but the suddenly a complete
>> cessation. Aha.
>
> Yes, I do see the discharge switch-off whilst a finite current still flows.

Ahh, very much in line with some of the old literature. Others show
undiminished current pulses, which then switch off. I think that's maybe
what mine does.

>> Hey Tony, I like the idea of a sense resistor - I'll try that too.
>
> Don't forget that you must use a current-shunt whose value is small

> compared with the discharge "resistance" in the die ...

Yes, I'm like your 2 ohm value, maybe 2.5 ohms with four 10-ohm surface
mount resistors, matched to a 50-ohm coax. Thankfully my 500MHz scope
has a 1mV/div imput. I have some of those fast Tek current probes,
the little ones you slide a wire through, but I don't think they'll
match the 0.7ns risetime of the scope.

> However, this is a relevant place to return to that photosensitivity
> question. I have previously reported that shining a torch beam onto
> the zener drastically reduces the size of the oscillations. Silly me,
> the answer is obvious now.... shining the torch beam onto the zener
> simply causes it to generate a photocurrent that drains off some of
> the 50uA stimulus (sideways) and the operating point of the relaxation
> osc just moves downwards under a reduced stimulus. In fact, you can get
> an estimate of the photocurrent by pushing the stimulus back up until
> it returns to the original picture.

Not only that, but it provides more carriers. For the lowest-voltage
microplasma site you may be normally seeing, it speeds it's repetition rate.
For other sites, it may lower the starting threshold so they can now join
the action.

A standard method for measuring M was to shine light on the junction and
measure the increase in electron flux over the photoelectron flux without
bias. If the light was a very small spot, which could be moved about, a
light-emitting portion of the junction could be specifically checked for
microplasma activity.

> Just a remark here. I am reasonably happy that external shunt-C up
> to about 10nF will not materially affect the avalanching mechanism that
> is seen just on the diode itself. But the joules required to kick larger
> values of external C may distort the experiment.

Yes I agree. My test diode seems to act toally different with a 0.1uF -
more like yours do with lower capacitances. I don't understand what's
going on in that instance, but haven't thought much about it or explored
that yet. For example, how does the diode even know about the external
capacitor? Maybe the much higher energy available for a short time is a
fsctor. Also as you suggest, internal resistances make be a key.

I think we're having fun now!

Winfield Hill

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Aug 6, 1997, 3:00:00 AM8/6/97
to

slo...@sci.kun.nl, <slo...@sci.kun.nl> said...

>
> hi...@rowland.org (Winfield Hill) wrote:
>> Bill Sloman, <slo...@sci.kun.nl> said...
>>>
>>> R.J.McIntyre "Theory of microplasma instability in silicon" J.Appl.Phys.
>>> volume 32 pages 983-95 (1961) looks promising. ...
>>
>> OK, I got it, but it's not so interesting, ...
>
> Our library did have it buried in the stacks, after all,

Ah, you can get the '63 paper, and then maybe even the earlier JAP papers.
But the really interesting ones are some of the Physical Review papers.

> the introduction does have a few interesting features. Fig 7 on page 987
> shows two typical current pulse shapes for diodes with high and low bulk
> thermal resistances respectively, ...

Well, I didn't mean to disparage McIntyre's paper, and figure 7 is a nice
picture, showing explicitly what ealier authors had described in writing.

> Fig 8 also describes the inital current spike which Win can find with his
> fast scope and probe - on the previous page the text says "Generally this
> transient to I'1 is too fast for an oscilloscope to follow .." but that
> was back in 1961.

Yes, he shows the benefit of local capacitance to maintaining a higher voltage
in the beginning, the observations in these papers don't support much more than
0.1mA current in a microplasma, even at the start, and generally argue each
microplasma acts separately. I read them more carefully to see if there's a
good theoretical basis for the limited microplasma size, although many admit to
the possibility of growth and some assert the same.

> So my scepticism about his interpretation of his observations seems to be
> ill-founded. Pity. That initial spike looked very inductive. I might add
> that I wouldn't dream of questioning the raw data he adduced.

Thanks, Bill. If you smile, you can question it anytime you want! ;-)

>> Yeasssss!!! Here, buried in our library's stacks, I found the real mother
>> lode: A dozen papers, reporting electron multiplication and avalanche

>> breakdown studies, starting in 1953 and extending for 10 years...


>> They're mostly in Physical Review, but a few of the later ones are

>> in the Journal of Applied Physics (JAP).


>>
>> Bill, these papers totally support and flesh out both the microplasma theory
>> and the large-M breakdown mechanisms - just as I've been suggesting that you
>> consider more seriously. They also include extinguishment aspects similar to
>> to some of the mechanisms in the IMPATT and SPAD diodes you've mentioned, but
>> perhaps with somewhat different time scales.
>

> McIntyre uses a 1psec transit time across the junction ...

Yes, those electrons are very speedy indeed. Although others place it somewhat
10x slower.

>> First, we have K.G. McKay and K.B. McAfee in 1953 (91, 1079), and continuing
>> with McKay in 1954 (94, 877). Their junction evidentally had a small number
>> of lower-voltage sites, and breakdown would commence with a single site
>> running at its full current (say 50uA), with 0.5 to 2us "pulse-width
>> modulation" durations. After increasing the total junction current to over
>> 50uA, this site would be on continously, and a new site would start, say at
>> 32uA. And etc.
>

> McIntyre cites G.L.Pearson and B.Sawyer Proc IRE volume 40 page 348 (1952),

I'd like to see that paper - perhaps they deserve more credit for the story,
although McKay at Bell Labs seems to have been a dominant player in the
beginning, identifying the simularity of high-voltage zener breakdown to that
of the Townsend avalanche process in a gas (although in a footnoe they thank
D.J. Rose for suggesting this). Neither Pearson nor Sawyer show up in the
subsequent literature, except when referenced for breakdown slopes and
temperature coefficient data and studies. Ahhh, and except for the 1958
Chynoweth and Pearson paper you mention below.

> and K.G.McKay Phys.Rev. volume 94 page 877 (1954).

Yes I have that paper (see 20 lines above).

>> Also in 1954, P.A. Wolff (95, 1415) writes a theory paper and says that the
>> mean-free path for electron-phonon interaction is 200A, but for ionizing
>> electric-field strengths (6x10^5 V/cm), it drops to 15A for electron-hole
>> pair production. This helps set the stage for very small plasma sizes.
>>
>> Then in 1956 come A.G. Chynoweth and K.G. McKay "Photon Emission from
>> Avalache Breakdown in Silicon" (102, 369), who say the microplasmas are a few
>> hundred A in diameter and occur at many separate places, and that these
>> microplasmas also emit light (!), probably when energetic electron-hole pairs
>> recombine. The emitted photons had between 1.9 and 3.1 ev of energy, peaking
>> at 2.2 ev, and occurred at a low rate relative to the electron current.
>> (Light emission was first reported in 1955, but not localized.)
>

> As Win suggested. He didn't use it to explain anything, though ...
>
> McIntyre cites this paper as A G Chynoweth and G L Pearson
> J.Appl.Phys,. volune 29 1103 (1958).

Hmmm, I missed that later reference (I hope our JAP collection goes back that
far). Perhaps they have more detail.

>> Incidentally, Chynoweth and McKay are the first I see in the literature
>> using the term "microplasma" and they don't reference it to someone else.
>>
>> Then we have D.J. Rose "Microplasmas in Silicon" (105, 413) in 1957 who
>> suggests chance-fluctuation current decreases for terminating a microplasma.
>> He uses a 500A microplasma size, and estimates a 36C temperature rise in
>> the microplasmas, which he uses to argue for a slightly reduced ionization
>> coefficient and a failure to simply reignite. He estimates both transit
>> times and thermal time constants of about 0.1ns.
>

> I am a lot happier with a 36C temperature rise in a microplasma, rather
> than a 360C rise in a mesoplasma. And I was perfectly happy to latch on
> the multiplicity of avalanche sites, which solved one problem with the
> self- extinguishing avalanche model. It was just that your "mesoplasma's"
> seemed to be getting more complicated than the data demanded.

Hey Bill, I may not have gotten the name right, but my concept was appropriate.
Don't be so hard on my "Speculation Hat ON" plus WAG calculations - that's what
disclaimers are for anyway!

Nonetheless, I still have the problem that very high currents that must flow,
all at once, to create my -100 to -200mV spikes in just 1ns, and even the rare
-0.4V or -0.5V spikes I've seen. At first glance, this simply isn't supported
by any of these papers.

Then I have the case for my diode with 1000pF, which shows a nice classic step
and pulse of discharge, mentioned in McKay and McAfee's first paper and many
since, and in McIntyre's graph. So that's nice, except my current is 4mA
instead of 0.1mA.

Both the spike and the pulse look like single events and still puzzle me. The
latter must be a single event because of the step on and off (which I'm going
to recheck). If the higher current I observe is occurring in a small region,
then we're obviously seeing a higher temperature, etc. etc.

I'm also beginning to wonder if my test diode is unique - I've only looked at
two diodes for Pete's sake! Maybe this one part is a total anomaly.

> What is important is that you have found the academic work on the subject
> that lets us interpret our observations in a reasonably self-consistent
> way, without having to waste the time elaborating our own theories. Who
> knows - Mike <NoS...@Today.Thanks> may even elaborate his Spice model for
> his zener diode to include these effects - though his most recent post
> had him barking up some other tree.
>
> Of course, when he uses the elaborated model to simulate his
> transistor-zener regulator, it may take a while for it to clock through
> enough 1psec steps to model it's turn-on transients. ...

Actually, I don't think it would be too hard to create a useful Spice model of
all this. A small number of microplasmas could be created and run in parallel
with slow nanosecond-timescale noisy pulse widths, adding up on avearage to
the desired zener current.

slo...@sci.kun.nl

unread,
Aug 7, 1997, 3:00:00 AM8/7/97
to hi...@rowland.org, to...@ledelec.demon.co.uk

In article <ant06202...@ledelec.demon.co.uk>,

Tony Williams <to...@ledelec.demon.co.uk> wrote:
>
> In article <5sac5j$l...@fridge-nf0.shore.net>, Winfield Hill
> <URL:mailto:hi...@rowland.org> wrote:
<snip>

> > I assume you're referring to a voltage waveform something like this,
> > from my earlier post (no parallel capacitor):
> >
> > ,| | |, | , ___+150mV
> > |||| ||: || |
> > |||| |, |||| ||:||
> > ,._,.-,-_.,I||I,-.I|L|,_.-,_,._,.-||II,._,.-,-I||II|, __ 0mV
> >
> > scope trace at 100uA, scattered events (5us/div)
> >
> > Ahh, yes, we do seem to have a nice steady current flowing between the

> > spike events, which is a little too high for one fully-saturated


> > microplasma, and must be some type of quiet mode of several microplasmas
> > working together....

More WAG. What do we know about the current-carrying capacity of a single
avalanche/microplasma site? And how do we know it?

> > When the spiking starts, it's just the regular stuff we had before the
> > steadiness.
> >
> > As to what starts this, Bill suggests it's the same process which all the
> > researchers seem to agree upon for stopping a microplasma (that ending step
> > you see). The steady current, which is a low near-starving level for
> > maintaining high M in the microplasma, randomly stops for a very small
> > fraction of a ns, afterwhich the microplasma remains off. A modest raised
> > temperature of a microplasma channel (if not too high) can help provide a
> > basis for it not to immediately restart, staying off long enough for all
> > the nearby carriers, previously helping sustain the current flow, to be
> > swept away during one of these hesitations.

I'm not sure I like the wording here. The avalanche doesn't "randomly
stop for a very small fraction of a ns". It stops dead in a about a
picosecond - if McInTyre is to be believed - and it stops because the
random multiplication process required to sustain the current flow had
randomly come up with a multiplication factor of zero, which is to say
that a whole generation of charge carriers had made it across the
junction without generating any new charge carriers.

We don't need to postulate any "nearby charge carriers", nor do we need
to speculate how they might have helped to sustain the current flow,
which is convenient, because if they existed it would much more difficult
to explain how the avalanche abruptly stopped.

> > The thing that puzzles me is the apparent stability of the quiet flow.
> > Convinced now of the dominance of the microplasmas, and their high M, which
> > increases the current flow until each microplasma saturates, how can we
> > have these steady currents, which don't appear to exactly represent the
> > summation of fully-switched ON microplasmas? The answer could involve a
> > very rapid switching of these currents inside the junction with its
> > capacitance, and not apparent at the terminals. If I remember correctly,
> > one of the papers pointed out that when two microplasmas are running at the
> > same time, one switching on can influence the other to switch off,
> > possibly by dipping the local voltage slightly, etc. ...

McIntyre (1961)lists three mechanisms that might limit the current
flowing through a single avalanche site - spreading resistance,
space-charge effects and internal heating - and produces calculated
figures in terms of a cylinder of diameter l and length w, which isn't a
whole lot of use, but goes on to say that to explain measured
differential impedances of the order of 200R (not too far from Tony's
500R) it is necessary to assume that the microplasma occupies a cylinder
that is distinctly squat " it is necessary to assume that w/l may be
considerably below unity and possibly as small as 0.1".

If the current through the microplasma is stable, the avalanche process
must be being choked back to a level where impact ionisation at both ends
of the junction is producing just enough charge carriers - on average -
to sustain that constant current. Some of the voltage across the diode
must be being backed off in space charge or resistive drops to reduce the
voltage across the junction to that required to produce just enough
multiplication to sustain the avalanche. The self-heating of the channel
will also raise the avalanche threshold, and act to choke back the gain -
but rather more slowly. McIntyre adduces time constants in the region of
10nsec to 1usec.

Tony's work with lower currents and a slower scope may be seeing this.

He goes on to point out that self-heating of the whole of the junction
would have a bigger effect, with a longer time constant of the order of
10msec.

Tony Williams

unread,
Aug 8, 1997, 3:00:00 AM8/8/97
to

Ok, follow-up to my last post. More measurements, quite
interesting and I think significant.

After the scan of my stock I had a close look at the 5-off
BZX79C10s... they were all from the same packet, in fact next
to each other on the tape... One was my slow C10, another was
a "medium speed" and 3 were fast.

So I carefully scoped the mean volts and amps for all 5 diodes
under the same conditions.... 50uA, 9400pF shunt-C.

I don't think it has relevance, but I changed the 22k feed-R
for a 180k in order to make sure that the stimulus-I stayed
more constant during the dynamics.

Results below, quite an interesting pattern emerging, note
the apparent peak discharge currents in the 9400pF.

I can see some interesting possibilities for explanations
emerging. But I'm going to keep mouth shut and just present
the raw data.

---------------------------------------------------------------

1. Waveform off 3 of the diodes, more or less the same picture.

Volts.
/\ /\ /\ /\ +ramp= 5.6mV/uS
/ \ / \ / \ / \--- 10-15mV pk-pk
/ \/ \/ \/ \ Tdischarge= 0.8uS, RC?, don't know.

Amps
--+ + ----- +50uA
| |______ -60uA
| /
|/________ -100uA
| ________ ? maybe a current spike. (hint1)


The waveform is totally with that 10-15mV pk-pk band.

Inserting the 100R in series with the 9400pF did
cause significant change to the volts-picture so take
that current waveform with a pinch of salt ( or give one
of those to Win to look at with his fast scope) (hint1a)

---------------------------------------------------------------

2. Waveform off 1 diode.

Volts.

/\ /\ /\ /\ _____

/ \ / \ / \ / \--- 6-12mV pk-pk |


/ \/ \/ \/ \ |
\ / |

\ / +ramp= 5.4mV/uS |
\ /---------------------------- 20-25mV pk-pk
\ / Tdischarge= 2uS, RC. |
\ / |
\/__________________________________|__

Amps
--+ + ----- +50uA
| |______ -60uA
| /
| /
| /
| /
|/_____________ -150uA
|______________ ? maybe, don't know. (hint2)


80% of the time is spent in that 6-12mV, but for 20% of the
time there are larger excursions as an early discharge
fails to shut off. I could only resolve the big V/I pictures.

---------------------------------------------------------------

3. Waveform off one diode, my usual C10. This sketch NTS.


Volts.
/\ /\ /\ _____
/ \ / \ / \--- 10-20mV pk-pk |
/ \ / \ / \ |
\ / |
\ / +ramp= 5.3mV/uS |
\ /---------------------------- 80-100mV pk-pk
\ / Tdischarge= 5uS, RC. |
\ / |
\/__________________________________|__

Amps
--+ + ----- +50uA
| |______ -50uA
| /
| /
| /
| /
|/_____________ -300uA
|______________ ? think not. (hint3)

80% big swings, only 20% within that 10-20mV band.

Bill Sloman

unread,
Aug 8, 1997, 3:00:00 AM8/8/97
to

>> Just a remark here. I am reasonably happy that external shunt-C up
>> to about 10nF will not materially affect the avalanching mechanism that
>> is seen just on the diode itself. But the joules required to kick larger
>> values of external C may distort the experiment.
>
> Yes I agree. My test diode seems to act toally different with a 0.1uF -
> more like yours do with lower capacitances. I don't understand what's
> going on in that instance, but haven't thought much about it or explored
> that yet. For example, how does the diode even know about the external
> capacitor? Maybe the much higher energy available for a short time is a

> factor. Also as you suggest, internal resistances make be a key.

Should we consider the internal inductance of the bigger capacitors? The
Philps ESR versus frequency curves for ceramic capacitors show a sharpish
resonance at about 10MHz for 100nF capacitors, rising to about 100MHz
for 100pF types. Their data for film parts is similar, if shifted to
slightly lower frequencies.

The avalanche seems to turn on and off at sub-nanosecond speeds, so at
these transitions, the external capacitor is actually a parallel inductor.

Winfield Hill

unread,
Aug 8, 1997, 3:00:00 AM8/8/97
to

Tony Williams at to...@ledelec.demon.co.uk says...
>
>1. Waveform off 3 of the diodes, more or less the same picture.
>
> Volts.
> /\ /\ /\ /\ +ramp= 5.6mV/uS
> / \ / \ / \ / \--- 10-15mV pk-pk
> / \/ \/ \/ \ Tdischarge= 0.8uS, RC?, don't know.
>
>Amps
> --+ + ----- +50uA
> | |______ -60uA
> | /
> |/________ -100uA
> | ________ ? maybe a current spike.
>

Hah! Certainly looks like an oscillator!

I'm a bit confused by your current waveform and labelling...
Does it imply the diode current is like this:

--+ + ----- 0uA
| |______ -110uA
| /
|/________ -150uA
|


I'm also interested in the current decay. Is there a chance
stretching out your waveform might look like this:

__ _ ____ _ 0uA
| ____| |____| _ ?
| _ __ ____ ____ __| _ 110uA
|__| ___| |__| |_| || _ 150uA
|

Anyway, you get the idea: steady levels, multiples of say 40 to
50uA etc. rapidly switching on/off to provide the averages you see.
I assume the waveforms you see are somewhat noisy.

Winfield Hill

unread,
Aug 8, 1997, 3:00:00 AM8/8/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...

>
> Winfield Hill <URL:mailto:hi...@rowland.org> wrote:
>> Tony Williams at to...@ledelec.demon.co.uk says...
>>> In fact, the "dc-current" that any ammeter sees, say at 50uA,
>>> is actually an integrated version of the succesive capapacitor

>>> charge/discharges. It puts a nice little twist on what precisely
>>> causes the shape of the knee of a zener.
>>
>> That's an astute observation. What "Joe Engineer" should take away
>> from this thread is the fact that modest zener currents are often
>> made up of pulse-width averages of discrete current levels, crudely
>> speaking.
>
> Well, the smooth curve of a zener knee is what started this
> particular thread. We all think (thought!) 'leakage' caused it.

At this point we have an interesting picture of silicon-junction
avalanche breakdown, i.e. zener diode operation. It's an exotic
picture, not one usually put forward for our understanding of the use
of zener diodes.

We're told in a series of papers in Physical Review by K.G. McKay, A.G.
Chenoweth, D.J. Rose, P.A. Wolff and S.L. Miller, in the mid-1950's,
that the junction current is not constant, but consists of current
through small microplasmas, turning on and off at different microscopic
locations within the junction. When on, each microplasma runs at full
strength, typically from 50 to 100uA in the junctions they used.

Following Tony's approach of measuring current rather than voltage, I
set out to look for this in my Motorola 1N5245B test zener. Motorola
provides an extensive characterization of this series of zeners,
"general data 500mW" page 6-2 in the 1994 TVS/Zener book, including 18
figures and 12 tables, but you won't find any information about this
very fundamental operating parameter for zener diodes.

I used a very simple setup (below). All the zener flows through the
terminating resistor at the end of a coax cable, which is 50-ohms to
provide a 20uA/mV observation sensitivity. I soldered the short zener
leads right onto the end of the coax.
____ ___
'-- zener ----)____ --- __)--+-- scope input
supply ----- 100k ----+--- 0.1uF ---+ coax 50-ohm
shield feedthro terminator

Running the zener at 17uA, bypassed with a big capacitor, I hoped to
see the microplasma current-discharge activity under the condition of
constant voltage (currents up to 100uA would only drop the zener
voltage by 5mV).

It worked very well. The diode was quiet most of the time, but erupted
into microplasma discharges often enough to consume 17uA on average.

The uniformity of microplasma currents was very apparent. For my
diode, they all were about 40uA. Therefore the total zener current, a
function how many microplasmas were running at once, was always some
multiple of 40uA. Of course, since my average supplied current was
only 17uA, the higher 40*N currents could only be sustained for a small
fraction of the time, and most of the time the diode would be off, as
expected. It's this aspect about which the average zener user is
unaware, myself included a month ago.

A typical example shows a 1us event after of a period of say 10us of
quiet.


3 primary levels: _ _| the shortest spikes are <5ns
40 - 80 - 120uA __| || |____ ______
____| | |____
0 ________________| |________
i----- about 1.0us total -----i


With q=it charges of about 44, 24 and 4pC removed by the first three
40uA microplasmas, the total 73pC event discharged the 0.1uF capacitor
only v = q/C = 0.73mV. In addition, we note that when no zener current
flowed, the 0.1uF would charge less than 2mV. So even though the zener
current had been zero for 10us, and suddenly stepped up to 120uA (over
7x our 17uA standing current) in a 1.0us event, this would not have
been very noticeable by monitoring the voltage, except as some "noise."

The rise and fall times were generally faster than my scope can show in
single-shot mode, or 2ns. Not shown on the trace above, but often
apparent, were short cessations of current, or new 40uA currents,
lasting a few ns or less. This caused a grassy trace in places.

At higher average zener currents, I would sometimes see sustained
plateaus of current at say 240uA, lasting up to 10us.

Tony, I think anyone should be able to see this kind of activity, even
with a slow 20MHz scope, if you have a 5 or 2mV/div scale, although a
digital storage scope certainly simplifies things. It's most
remarkable when at low zener currents, like 10uA. I think these
microplasma steps are responsible for all the small increases in
current, above the say 0.6uA/V leakage slope, in the early knee of the
zener breakdown. This starts at about 14.345 V for my 15V diode, and
gets well underway with a modest 10mV (+0.06%) higher voltage:

volts current
10 5.1 uA
12 6.5
14 7.6
14.340 8.5
14.345 10.1
14.350 18.7
14.355 37.1
14.356 46.2
14.357 60.1
14.358 100 uA

You'll note that the zener impedance is about 25 ohms at 100uA, far
below the roughly 200 ohms Motorola implies in figure 8 of the data
sheet. I saw no evidence of any effects from bulk resistance, etc. in
my measurements.

But I wondered, what sign was there of the much higher current pulses I
had observed with this same diode, without any parallel capacitance?
Adjusting the trigger threshold to a higher level, the scope would
trigger only rarely. Playing with the average current, here's the
highest spike I saw, dropping 20mV across the 50-ohm scope resistor.

400uA _
|
||
||
| \
| |
quiet: = =
up to | |______ _ 80 uA
300 us! | |__ _ 40 uA
__________| |_____

OK, out of time, that's all for now. But don't worry, Bill, despite
the rare 400uA absolute maximum spike mentioned above, I was able to
see my giant >5mA ns-long spikes just fine, and now understand why they
dominate, when running my zener without a bypass capacitor. In fact,
the reason became apparent to me before my technician finished the
2.5-ohm surface-mount test fixture, making the measurements somewhat
anticlimatic. Challenge for the day, readers: with some thought, you
may see it as well.

Here's a smasher hint, the zener voltage waveform with 114pF of total
capacitance, at 50uA. The discharge step takes well under 2ns (the
limit of my measurement).

14.63V ________
\ -0.31V step
\________
14.32V

Tony Williams

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Aug 8, 1997, 3:00:00 AM8/8/97
to

In article <5sfdvc$d...@fridge-nf0.shore.net>, Winfield Hill

<URL:mailto:hi...@rowland.org> wrote:
>
> Tony Williams at to...@ledelec.demon.co.uk says...
> >
> >1. Waveform off 3 of the diodes, more or less the same picture.
> >
> > Volts.
> > /\ /\ /\ /\ +ramp= 5.6mV/uS
> > / \ / \ / \ / \--- 10-15mV pk-pk
> > / \/ \/ \/ \ Tdischarge= 0.8uS, RC?, don't know.
> >
> >Amps
> > --+ + ----- +50uA
> > | |______ -60uA
> > | /
> > |/________ -100uA
> > | ________ ? maybe a current spike.
> >
>
> Hah! Certainly looks like an oscillator!
>
> I'm a bit confused by your current waveform and labelling...
> Does it imply the diode current is like this:
>
> --+ + ----- 0uA
> | |______ -110uA
> | /
> |/________ -150uA
> |

Our posts are crossing. My waveform at the top is still the
current in the external 9400pF... you are already off onto
measuring with the current-shunt in series with the zener.

I have read your other post and have put a shunt in series
with a zener, just for a quick look. Later this evening I
will do some measurements, but a preliminary glance showed
that it is almost precisely your sketch above, if it were
to be inverted. I may be able to reply to the other post
in a few hours. (I feel it diplomatic to consult with my
social secretary first, aka SWMBO).

There is something there you haven't commented on yet....

(9400+100)pF, say, is being shifted by about 12mV in 0.8uS.
ie Q = CV, 9500pF * 12mV = 114 pC.

In the top sketch, say 80uA linear for 0.8uS, = 64 pC.

The discharge is (114-64), 50pC, short.

I think I can see a spike about 200nS long at the front edge
of the current waveform... 50 pC = I * 200nS, I = 250uA.

Now, I also reported that inserting the 100R shunt does
disturb that particular waveform and I do suspect that the
250uA front edge may be considerably larger.

I am trying to confirm to you that the discharge does appear
to be a two-step process... a big short gulp (maybe time-limited?)
followed by a more leisurely discharge until about 100uA zener
current. This is what I think you mentioned after your first
look for yourself.

That post with the three pictures on was also trying to show
the variance across diodes.... the differences in the size of the
first gulp and the subsequent leisurely discharges.


> I'm also interested in the current decay. Is there a chance
> stretching out your waveform might look like this:
>
> __ _ ____ _ 0uA
> | ____| |____| _ ?
> | _ __ ____ ____ __| _ 110uA
> |__| ___| |__| |_| || _ 150uA
> |
>
> Anyway, you get the idea: steady levels, multiples of say 40 to
> 50uA etc. rapidly switching on/off to provide the averages you see.
> I assume the waveforms you see are somewhat noisy.


I have had a quick look... No, I see no sign of the discharge
current shifting in discrete steps. Yes, a continuously
scanning scope is noisy. Although you can get a lock, what you
see is many discharges overlaid on the screen. I will re-look
because you are obviously pursuing a line of thought here but
don't build your hopes up too much.

It would be really useful if someone else with a storage scope
could also do these experiments and get some confirmations.

(Hint, hint)

Tony Williams

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Aug 9, 1997, 3:00:00 AM8/9/97
to

In article <5sf7rb$6...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:
>
> Tony Williams, <to...@ledelec.demon.co.uk> said...
[snip]

Ok Win, I put a 50R current-shunt in series with the zener, instead
of my original 100R in series with the 9400pF cap. But not with the
extreme tidiness of your circuit above.

First Result:-

At 50uA stimulus I was pleased to see nearly exactly inverted
versions of the cap-current, when corrected for the 50uA stimulus
flowing in the zener at different times...... Good.

Second Result:-

I went down to low current, to the region I originally called Mode.1.
In this region the zener is just starting to fire, random snaps and
not yet really looking like a repetitive relaxation osc. At 17uA
my diodes would appear to be already in Mode.2, so I had to go down
to the 1-5uA region.

I did not see any zener currents with discrete steps. What I saw,
over several diodes, were fixed-amplitude current pulses about
80-100uA in size and about 200nS in duration. At 9400pF shunt-C
the pulses had a slight ramp and with 0.22uF across that they were
nearly flat-topped.
-------------------------------------------------------------------

I repeat here my thoughts on this 2-step discharge, in Mode.2:-

Discharge.1 (D1) is probably voltage-triggered, short-lived, and
with the possibility of a high current flow. Across my stock of
zeners diodes I see a wide variation in D1-capability. This means
that a D1 may or may not be strong enough to pull all the Charge
out of whatever circuit-C there may be there, by itself.

D1 is the current where you are seeing stepped increments, possibly
from various discharge-sites conspiring together every now and
again. I have not yet seen this but have noted a tendency for
the leading edges of the current to be jumpy... I will go back
and see if there are any integer relationships visible.

Discharge.2 (D2) follows on from D1, triggering unknown, probably
actually triggered by D1. D2 for me is always exponential and the
source resistance has been measured from 500R to less than 100R.

There is a clear tendency for zeners with a large D1 to be at the
lower source-R in D2, and vice-versa. eg, My slow C10 has negligible
D1 and is up at 500R for D2 whereas the "fast" C10 has a big D1 and
in D2 the discharge-R is <100R. Instinctively that does make sense.

For all diodes I have looked at, D2 always ends with a finite current
flowing, around the 80/120uA region and I would suggest that the
stopping mechanism for the D2 discharge *is* current-related.
-------------------------------------------------------------------

[V/I characteristics]

>This starts at about 14.345 V for my 15V diode, and
> gets well underway with a modest 10mV (+0.06%) higher voltage:

>
> volts current
> 10 5.1 uA
> 12 6.5
> 14 7.6
> 14.340 8.5
> 14.345 10.1
> 14.350 18.7
> 14.355 37.1
> 14.356 46.2
> 14.357 60.1
> 14.358 100 uA
>
> You'll note that the zener impedance is about 25 ohms at 100uA, far
> below the roughly 200 ohms Motorola implies in figure 8 of the data
> sheet. I saw no evidence of any effects from bulk resistance, etc. in
> my measurements.

Yes, I did this plot as well, but take care with your conclusions.

If you do it over smaller current increments and measure the dV/dI
for every increment you may see the zener impedance varying from
+200R to -200R in small regions over the range 5 to 100uA. I did it
with 10uF and 10uA steps to see this but also caught tantalising hints
of more rapid changes in Zout in certain places. I think a plot of I
at 10mV increments, then dV/dI, may produce some interesting results.
-------------------------------------------------------------------

For the record, I also did a series of gross measurements, fwd drop
mV/decade, rev slope resistance, etc. I see no signs of a correlation
between any bulk-silicon results and the oscillation activity.
-------------------------------------------------------------------

I've stuck my neck out so much on this 42-Job that I'm not
even going to think about what that is.

Winfield Hill

unread,
Aug 9, 1997, 3:00:00 AM8/9/97
to

Tony Williams, <to...@ledelec.demon.co.uk> said...
>
> Winfield Hill <hi...@rowland.org> wrote:
>>
>> We're told in a series of papers in Physical Review ... the junction
>> current is not constant, but consists of small microplasmas, turning

>> on and off at different microscopic locations within the junction.
>> When on, each microplasma runs at full strength, say 50 to 100uA.
>> [big snip] I used a very simple setup [snip] Running the zener at
>> 17uA, bypassed with a big capacitor, ... [snippity] The diode was

>> quiet most of the time, but erupted into microplasma discharges
>> often enough to consume 17uA on average.
>>
>> The uniformity of microplasma currents was very apparent. For my
>> diode, they all were about 40uA. Therefore the total zener current,
>> a function how many microplasmas were running at once, was always
>> some multiple of 40uA. [snip]

>>
>> 3 primary levels: _ _| the shortest spikes are <5ns
>> 40 - 80 - 120uA __| || |____ ______
>> ____| | |____
>> 0 ________________| |________
>> i----- about 1.0us total -----i
>>
>> [snippity snip]
>> Tony, I think anyone should be able to see this kind of activity...

>
> Ok Win, I put a 50R current-shunt in series with the zener, instead
> of my original 100R in series with the 9400pF cap. ...

> At 50uA stimulus I was pleased to see nearly exactly inverted
> versions of the cap-current, when corrected for the 50uA stimulus
> flowing in the zener at different times...... Good.
>
> Second Result:-
>
> I went down to low current, to the region I originally called Mode.1.
> In this region the zener is just starting to fire, random snaps and
> not yet really looking like a repetitive relaxation osc. At 17uA
> my diodes would appear to be already in Mode.2, so I had to go down
> to the 1-5uA region.
>
> I did not see any zener currents with discrete steps. What I saw,
> over several diodes, were fixed-amplitude current pulses about
> 80-100uA in size and about 200nS in duration. At 9400pF shunt-C
> the pulses had a slight ramp and with 0.22uF across that they were
> nearly flat-topped.

Aha, yes. Now I am focussing in on the issue of your declining current
during each event. Can we ascribe this kind of activity to a single
microplasma?

We need to more agressively address the issue of the size of each
microplasma's current. In the early literature I cited, it was
generally stated that the size of the microplasma might increase (e.g.
for larger currents) and that this hadn't been established. Several
papers asserted that it did, but without good evidence.

Yesterday, however, I scanned other paper, "Light Emission and Noise
Studies of Individual Microplasmas ..." by A.G. Chenoweth and K.G.
McKay, in J.A.P. 30, 1811 (1959). [These two fellows apparently spent
over 5 years working with ionization rates and microplasmas at Bell
Labs, and Chenoweth later became Head of Materials Science.] In this
study, they carefully examined each tiny microplasma spot with a
microscope and also measured its brightness with a PMT as they
increased the current.

They used a "large condenser" to insure a steady voltage during the
microplasma discharges.

For a current of 0 to almost 200uA, only one microplasma was active
(having become visible at 50uA). However, the "basic microplasma size"
was about 100uA. Above 100uA, the current flow was stable (not
switching on and off) and increased. At some point an additional 100uA
microplasma was observed switching on and off in the current traces.
By 200uA, it was visible optically. They say the 3rd and 4th
microplasmas didn't start current on/off activity until 320 and 700uA.
Therefore a current of up to about 1.1mA was carried by just four (4)
microplasmas, implying at least a 2.5x expansion capability, although
two of the microplasma no doubt exceeded that. So these measurements
and others they made clearly implied that a single microplasma can
carry a sustained current well above it's step starting level.

However, Chenoweth and McKay went further stating,

"... though the magnitude of the current instability is
constant for a given microplasma, increasing the bias
slightly causes the microplasma to become stable while
its current increases with bias. In this latter region,
the linear dependence of the light intensity on the net
current shows that the cross-section area of the micro-
plasma, perpendicular to the direction of current flow,
must increase linearly with the current."

Of course, we have McIntyre's later paper, which Bill likes to quote,
showing a slope (fig 7), but the compelling measurements in Chenoweth
and McKay's paper, not to mention Tony's new measurements, make this
seem more acceptable.

Next, let's consider again the measurements I made with the single
(ha!) diode I have studied. I've added a few more points plus some
spreadsheet calculations:
---- microplasma -----
total plasma (single =40uA)
>> volts current current %duty excess
>> 10 5.1uA 0.0uA 0.0%
>> 12 6.5 0.0 0.0
>> 14 7.6 0.0 0.0
>> 14.340 8.5 0.7 1.7
>> 14.345 10.1 2.3 5.7
>> 14.350 18.7 10.9 27
>> 14.355 37.1 29.3 73
>> 14.356 46.2 38.4 96 0x
>> 14.357 60.1 52.3 100 0.3x
>> 14.358 100 uA 92.2 100 1.3x
14.359 150 142.2 100 2.6x
14.360 190 182.2 100 3.6x

Now a different picture emerges. Notice the extreme current increase
with a small change in voltage. On a graph it's a striking slope.
From 14.357 to 14.360, a change just 3mV, we can see a nice straight
line from 52 to 182uA, with each data point right in place. If treated
as a dynamic resistance, this is an amazing 23 ohms from 50uA up.

Before Tony objects, let me argue this is very real: my diode doesn't
start playing negative-resistance games (another subject deserving our
microscopic examination) until another 10 to 15mV and 400 to 600uA.

Continuing the line of thought, we know that my diode's "current
instability constant" as used in the paper above, is 40uA. So I
suspect that just above 40uA. just one microplasma is running much of
the time, possibly doubling its conduction with a voltage increase of
about 1.5mV (I'll check on the bench the next time I have a chance).

OK, here I'm very uncomfortable ascribing much significance to dynamic
resistance concepts, preferring to think instead about the huge effect
of small electric-field changes on the avalanche multiplication factor
and microplasma size.

Now let's return to Tony's statement:
"I saw .. fixed-amplitude current pulses about 80-100uA in size and


about 200nS in duration. At 9400pF shunt-C the pulses had a slight
ramp and with 0.22uF across that they were nearly flat-topped."

Now Tony's measurements make more sense to me. With a small 9400pF
capacitor, he can expect a -2mV drop in 200ns with 100uA. Consider the
effect -2mV has on the current for my diode! No wonder he sees a
slight ramp! On the other hand, with 0.22uF he doesn't see this ramp.
Yes, exactly. Now we all see this clearly.

I have lots more to say, but am out of time. SWMBO, etc.

>
> I've stuck my neck out so much on this 42-Job ...

Hey, Tony, keep the faith on this 42-business.
Remember, we're getting the answer to:

The Meaning Of Life, The Universe And Everything.

slo...@sci.kun.nl

unread,
Aug 9, 1997, 3:00:00 AM8/9/97
to hi...@rowland.org, to...@ledelec.demon.co.uk

<snipped lots of interesting stuff>

When I first started hypothesising about what was going on in these
diodes, I was figuring that most of the randomness came because the
avalanche would restart at a more or less arbitrary time, at just one
avalanche site.

Now it looks much more as if the uncertainty lies in when the avalanches
turn off.

What looks like a good way of explaining Win's large initial current
spikes is to assume that the voltage across the junction builds up to a
point where a number of the lowest threshold avalanche sites can turn on,
then when one turns on, all turn on.

The current through each site then rises rapidly until the total charge
transferred from the diode capacitance pulls the voltage down to the
threshold level or below.

Note that the current in the lowest threshold site will rise fastest, and
keep on rising longest. If the threshold voltages form a Gaussian
distribution, the lowest few threshold voltages will be more widely
spaced than the threshold's immediately above them, so that the bulk of
the current is likely to be spread over a lot of avalanche sites.

These low-current avalanches will decline as the substrate heats up and
the voltage across the junction continues to fall, and they will have a
high probablity of turning off due to statistical fluctuations in the
number of charge carriers, so that most of them disappear within
nanoseconds of avalanche initiation. The few lowest lying channels will
havebuilt up higher currents, and will last a lot longer.

Note that a channel has a higher chance of fluctuating down to one or two
charge carrier than it has of turning off, which would explain Win's step
patterns.

Now - why are Tony's results different? Tony only sees a significant
initial current surge on his worst diode, though some sort of initial
spike is visible with most of his diodes.

My hypothesis would be that in Win's diodes the theshold voltages are
more closely spaced - the standard deviation on the distribution would be
perhaps three times smaller than in Tony's diode - so that in Tony's
diodes many fewer channels get turned on , and the lowest-threshold
channel is the only one that survives the initial few nanoseconds. The
gap to the next lowest-threshold site determines how much current builds
up in the lowest-threshold site before the voltage across the junction
falls to the threshold voltage.

Tony Williams

unread,
Aug 10, 1997, 3:00:00 AM8/10/97
to

In article <5si38e$t...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:
[big snip]

> Aha, yes. Now I am focussing in on the issue of your declining current
> during each event. Can we ascribe this kind of activity to a single
> microplasma?
>
> We need to more agressively address the issue of the size of each
> microplasma's current. In the early literature I cited, it was
> generally stated that the size of the microplasma might increase (e.g.
> for larger currents) and that this hadn't been established. Several
> papers asserted that it did, but without good evidence.

[big snip]


> Now let's return to Tony's statement:
> "I saw .. fixed-amplitude current pulses about 80-100uA in size and
> about 200nS in duration. At 9400pF shunt-C the pulses had a slight
> ramp and with 0.22uF across that they were nearly flat-topped."
>
> Now Tony's measurements make more sense to me. With a small 9400pF
> capacitor, he can expect a -2mV drop in 200ns with 100uA. Consider the
> effect -2mV has on the current for my diode! No wonder he sees a
> slight ramp! On the other hand, with 0.22uF he doesn't see this ramp.

Hmm, my antennae go up when you start doing sums against a 2mV
dV across the zener.... at 100uA that 50-ohm current shunt has
already given you a 5mV dV-step. Plus, I keep muttering that
when the 50-ohm is inserted in series with a "fast" diode the
picture changes.... Is the test method modifying the results?

So, I put together a quick 2-pnp circuit to get rid of that 50
ohm shunt. The bottom of the zener was connected to pnp1, which
had 5mA emitter current and a 100-ohm collector resistance to
-15v. The scope was across that 100-ohm. pnp2 provided a +Vbe
for pnp1's base to sit on. At 5mA Ie in pnp1 the zener should
see 25/Ie, about 5-ohms instead of 50.

Results:- Below is the main I-shape and definitions for the results.


+------------------- I1, uA
|
|
+------------------- I2, uA
|\
| \
| \
| \
| +-------------- I3, uA
| |
| +-------------- W, width in uS. (approx!)
___| |_______

9400pF + Cstrays. 0.22uF added across.
------------------- -------------------
Idc I1 I2 I3 W I1 I2 I3 W

0.2 100uA, cannot lock. 90uA, cannot lock.
0.5 120uA, cannot lock. 100uA, cannot lock.

1 140 120 100 0.5 110 110 110 ?
2 150 140 100? 0.9 130 110 110 0.9?
4 180 140 110 1 150 120 120 ?
6 240 150 110 1.1 170 140 140 ?
8 270 150 100 1 200 140 140 ?
10 280 150 100 1.1 200 140 140 ?
15 310 150 100 1.1 250 140 140 ?
20 340 150 100 1.3? 300 150 130 10?
30 380 160 110 1.4 340 150 130 15
40 420 150 110 1.5 380 170 130 15
50 440 150 100 1.5 400 170 130 17?
60 480 150 110 1.6? 410 180 140 20?
70 500 150 110 1.7? 430 180 130 20?
80 500 150 110 2? 430 170 130 22?
90 510 160 120 2? 470? 180 130 22?
100 540 160 130 2? 480 180 140 30?
120 560 160 150 2? 500 180 150 30?
140 580 140 140 ? 500 150? 150? ?
160 580 150 150 ? 500 160? 160? ?
180 540... mode change, can't get a lock.

Notice the 140uA reading.... this is where I have previously
report the V-waveform as "going squarish" and it's nice to
get a confirmation from another direction. The characteristic
is that a previously ramping waveform has changed to being
horizontal. So, I tracked the current down to find the exact
point at which it changed.... about 135uA dc is the magic I.

There we go Win, shifting to a lower shunt-R does change the
I, particularly that front edge. Get your gnashers around that.

It's 12:51, Sunday Morn. I'm heading for a glass of Liebfrau
as a pre-prandial, before sitting down to beef and roast
potatoes.... and it's a 31C scorcher would you believe! Mad
dogs and Englishmen, or something.

Tony Williams

unread,
Aug 10, 1997, 3:00:00 AM8/10/97
to

In article <5si38e$t...@fridge-nf0.shore.net>, Winfield Hill
<URL:mailto:hi...@rowland.org> wrote:
[huge snip]

Nope, I'm not going to object because a reliable "dc" V/I plot
is almost impossible... both parameters are affected by the
zener oscillation. You can put a 10uF slug across it and still
not be certain whether the diode is hooting away inside it's
own little loop. To demonstrate that the table below is the
V/I for the diode in my previous post, at the same currents
and with same the shunt-C options. Note the different results.

9400pF + Cstrays. 0.22uF added across.
------------------- -------------------

Idc Vzener Vzener
0.2 10.153 10.154
0.5 10.151 10.156
1 10.154 10.157
2 10.159 10.157
4 10.163 10.162
6 10.165 10.163
8 10.168 10.163
10 10.168 10.164
15 10.170 10.165
20 10.170 10.165
30 10.173 10.166
40 10.173 10.169
50 10.173 10.169
60 10.171 10.169
70 10.172 10.170
80 10.174 10.170
90 10.174 10.171
100 10.173 10.171
120 10.169 10.172
140 10.169 10.173
160 10.170 10.174
20mV pk-pk avg. 12mV pk-pk avg.

Vzener, as seen by a DVM, is really the true Vzener +/- the
mean of the oscillation at the point of measurement. The above
shows how the conditions of test affect the readings.

However, do dV/dI on the tables above and it does show very
low "resistances" over this oscillatory range, 30 to 50 ohms
would be a reasonable guesstimate.

BTW. Slight perp. I had intended to do both these test tables
on the very fast C10, in order to maybe get something
equivalent to Win's 15v. Unfortunately I picked up the
wrong up, this is a medium-speed C10.

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