[online] PhD Thesis Colloquium of student Mr. Biswapriyo Das.

Skip to first unread message

Wladek Grabinski

Oct 14, 2020, 4:45:55 AM10/14/20
to mos...@googlegroups.com
FROM: Professor Santanu Mahapatra ( শান্তনু মহাপাত্র ) 
Nano Scale Device Research Laboratory
Department of Electronic Systems Engineering (formerly CEDT)
Indian Institute of Science Bangalore
Bangalore 560012 INDIA

Dear Colleagues, 
Hope you are in good health amid this pandemic.

I would like to invite you and your team members to the online thesis colloquium of my PhD student Mr. Biswapriyo Das. In our institute, it is mandatory for a PhD student to give an open colloquium for his research work just before the thesis submission. In pre-COVID time, it used to be a physical presentation, attended by the institute community. However, during this evolving pandemic we are conducting the colloquium online. It thus gives us opportunity to invite researchers across the globe who are working on the similar problems in device-modeling .

You may find the details of the talk below. Hope to see you and your group members on 19th October at 3PM IST. MS Teams Link:

Title:  Atom-to-circuit modeling strategy for 2D transistors

Abstract: Two-dimensional (2D) materials are now being considered as viable options for CMOS (complementary metal-oxide-semiconductor) technology extension due to their diverse electronic and opto-electronic properties. However, introduction of any new material in the process integration phase of technology development in semiconductor industry is an expensive and time-consuming affair. It is also a difficult task to select an appropriate 2D material from the plethora without assessing their performance at circuit level. Thus, first-principles-based multiscale models that enable systematic performance evaluation of emerging 2D materials at device and circuit levels solely from their crystallographic information is in great demand. In this thesis, such an atom-to-circuit modeling framework, addressing three different levels of abstraction (viz. material, device and circuit), has been demonstrated.
Firstly, the model was implemented for a van der Waal’s heterostructure based all-2D metal-insulator-semiconductor field-effect transistor (MISFET), comprising of vertically stacked semi-metallic graphene, insulating hexagonal boron nitride (hBN) and semiconducting monolayer molybdenum disulphide (MoS­2). Our physics-based compact model demonstrates the effects of band gap opening in graphene due to its sublattice symmetry breaking interactions with underlying hBN layer. This apart, we have also studied the effects of semiconductor doping and the band gap variation of graphene at device and circuit levels. The model equations were thereafter implemented in a professional circuit simulator using its Verilog-A interface to facilitate design and simulation of integrated circuits.
Secondly, the scope of the proposed model was further extended to capture the non-quasi-static (NQS) effects in 2D transistors operating at very high frequencies, typically greater than its intrinsic cut-off frequency fT. Taking phosphorene as a prototypical example, a multiscale NQS model was developed for 2D transistors that can predict the channel-orientation-dependent high-frequency performance of devices and circuits solely from the crystallographic information of their constituent materials. The material-specific parameters obtained from density functional theory (DFT) calculations were used to develop a continuity equation based NQS model to gain insight into the high-frequency behaviours. It was found that channel orientation has strong impact on both the low and high frequency conductances, however it affects only the high-frequency component of capacitances. The model was then implemented in industry-standard circuit simulator using relaxation-time-approximation technique and simulations of analog and digital circuits were carried out to demonstrate its applicability for near cut-off frequency circuit operation.
Finally, the idea was also exercised for modeling novel quantum materials like 2D topological insulators (TI) and it was shown that the proposed analytical approach could be useful for developing compact models of topological insulator field effect transistors. A k. p Hamiltonian based continuum model was used to unveil the bandgap opening in the edge-state spectra of finite-width monolayer 1T' molybdenum disulphide (MoS2), molybdenum diselenide (MoSe2), tungsten disulphide (WS2) and tungsten diselenide (WSe­2). It was shown that the application of a perpendicular electric field effectuates a topological phase transition and it can simultaneously modulate the band gaps of both bulk and edge-states. The tuneable edge conductance, as obtained from the Landauer-Büttiker formalism, exhibits a monotonous increasing trend with applied electric field for deca-nanometer MoS­2, whereas the trend is opposite for other cases.

[1] Das, B. and Mahapatra, S., “An atom-to-circuit modeling approach to all-2D metal-insulator-semiconductor field-effect transistors”, npj 2D Mater Appl 2, 28 (2018).
[2] Das, B., Sen, D. and Mahapatra, S., “Tuneable quantum spin Hall states in confined 1Tʹ transition metal dichalcogenides”, Sci Rep 10, 6670 (2020).
Santanu Mahapatra ( শান্তনু মহাপাত্র )
Nano Scale Device Research Laboratory
Department of Electronic Systems Engineering (formerly CEDT)
Indian Institute of Science Bangalore
Bangalore 560012 INDIA

Adjunct Faculty IIIT-Allahabad

Phone: +91-80-2293-3090
Home Page: santanu.dese.iisc.ac.in
Lab Page: nsdrl.dese.iisc.ac.in

Reply all
Reply to author
0 new messages