The thickness of a human hair ...
th...@btr.btr.com
breakthroughs (with semiconductors, nano-technology, etc.) as being "the size
and/or diameter of a human hair!"
Hmmm. Skeptic mode follows ...
I regularly use 0.005" and 0.002" silver wire, and I have no problems seeing
the 0.005" wire though I have to use a magnifier to view unspooled 0.002" wire.
So, whipping out my ol' micrometer, I measured hair diameter as found on
various body parts (which shall remain nameless! :-) and find that 0.008" is
the smallest I could find and/or see.
There's no way I can see (with the unaided eye) individual memory "cells" as
commonly found on [SD]RAM chips, yet the "press" constantly refers to those
cells as "the thickness of a human hair."
My "guess" is those RAM memory "cells" are 3 to 4 orders of magnitude SMALLER
than the diameter of a human hair.
So, is the "press" referring to cilia (as found on habitue' microorganisms) as
being "human hair", or is their standard-of-reference something else?
Please note the posting date is NOT April 1. :-)
Thad Floryan [ th...@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]
Thaddeus P. Floryan
>[...]
>BTW, I'm mildly surprised at your measurements - I thought hair was down
>around the thickness of a sheet of paper, 2 or 3 thousandths.
It all depends on how much trouble and/or pain one wishes to endure to find
a hair to measure! :-)
I originally clipped a few from various places, and measured those. I may
have mis-measured originally; I just "calibrated" the my interpretation of
the micrometer reading using auto feeler gauges (from 0.002 to 0.025 in 0.0005
steps), and reached 1/2 the reading of before (I'll have to find my original
post and see what time of day (I might have been asleep :-)).
Using a high-intensity lamp as a backlight, I found some others, and those
did measure 0.0011 - 0.0015".
Frankly, I was surprised (given the "problem" seeing 0.002" dia Ag wire);
though corrected (with glasses), my visual acuity was the best on a boat of
8 people a year ago in B.C., being able to see phone lines across the rivers
several miles away (which others couldn't even see using binoculars). Perhaps
it's the "color" of silver which renders it difficult to see.
Paper I've found around here measures 0.003 - 0.004" (yellow writing tablets
and fan-fold "computer" paper).
'Tis funny: in nearly 47 years I never bothered measuring a hair before! :-)
Back to the serious topic of measurements used in semiconductor manufacture:
is it not true that dimensions (or positioning accuracy) are often (always?)
expressed in terms of microns and/or Angstroms?
Those units are "small": I remember an Angstrom being a hundred millionth of
a centimeter, and a micron is the millionth part of a meter (or one thousandth
of a millimeter (or 0.0000393")). All definitely smaller than the diameter of
a hair! :-)
John Whitmore
es:
>Back to the serious topic of measurements used in semiconductor manufacture:
>is it not true that dimensions (or positioning accuracy) are often (always?)
>expressed in terms of microns and/or Angstroms?
Actually, the depths of diffusions are measured in microns
or Angstroms (or nanometers), while the lateral dimensions are commonly
in mils (thousandths of an inch). This is for historical reasons;
the literature that covered diffusion was scientific and used SI
units, while the literature that covered lithography was from
the printing industry, which measured in mils and inches.
Those lateral dimensions of interest only to the chip
designer (via widths, spacing rules) are small enough to
be inconvenient in mils, and are given (usually) in microns
where the numbers are of order unity. The die size and pad
dimensions (which would be of interest to a customer building
hybrids from the chips) are still specified in mils, however,
in the data sheets I've seen.
John Whitmore