Nov 2, 2020

Remember when the keyboard was the computer?

and in less than four (4) decades we are back: 

FROM Oric1:
a CPU (MOS 6502A @ 1 MHz) with 16KB ROM/48KB, Sound: AY-3-8912, Graphics: 40×28 text characters/ 240×200 pixels, 8 colours and simple connectivity - tape recorder I/O, Centronics compatible printer port, RGB video out, RF out, expansion port
TO Pi400:
a quad-core 64-bit @ 1.8GHz CPU Cortex-A72 (ARM v8) 64-bit (BCM2711) with 4GB RAM (LPDDR4-3200), wireless networking (IEEE 802.11b/g/n/ac wireless LAN, Bluetooth 5.0, BLE), dual-display output and 4K video playback it is ideal for surfing the web, creating and editing documents, watching videos, and learning to program using the Raspberry Pi
[read more: ]

[paper] SPICE Compact Model for Schottky-Barrier FETs

Sheikh Aamir Ahsan, Member, IEEE, Shivendra Kumar Singh, Chandan Yadav, Member, IEEE, Enrique G. Marín, Member, IEEE, Alexander Kloes, Senior Member, IEEE
and Mike Schwarz, Senior Member, IEEE
A Comprehensive Physics-Based Current–Voltage SPICE Compact Model 
for 2-D-Material-Based Top-Contact Bottom-Gated Schottky-Barrier FETs
IEEE Transactions on Electron Devices, vol. 67, no. 11, pp. 5188-5195, Nov. 2020
DOI: 10.1109/TED.2020.3020900

Abstract: In this article, we report the development of a novel physics-based analytical model for explaining the current–voltage relationship in Schottky barrier (SB) 2D material field effect transistors (FETs). The model has at its core the calculation of the surface-potential (SP) which is accomplished by invoking 2-D density of states in conjunction with Fermi–Dirac (FD) distribution for electron and hole statistics. The explicit computation for the SP, carried out using the Lambert-W function together with Halley’s method, is used to construct the SP-based band-diagram for realizing the transparency of the SBs. Thereafter, the ambipolar current is derived in terms of the electron and hole injection phenomena the thermionic emission and Fowler–Nordheim tunneling mechanisms at the SB contacts. Furthermore, drift-diffusion current is derived in terms of the SP and incorporated in the model to account for the scattering in the intrinsic 2D channel. Finally, the Verilog-A model is validated against experimental IV data reported in the literature for two different 2D material systems. This is the first demonstration of an explicit SP-based SPICE model for ambipolar SB-2-D-FETs that is simultaneously built on tunneling-emission and driftdiffusion formalisms.

Fig: (a) Band-diagram sketched along positive y-direction underneath the source electrode. Blue and black lines represent bands before and after applying Vgs. (b) ψ-based diagram sketched along positive x, constructed after calculating ψs and ψd. The geometrical screening length λ is given by λ ≈ (tox t2D)^1/2.

Acknowledgement: This work was supported in part by the National Project Implementation Unit (NPIU) through the third phase of Technical Education Quality Improvement Programme (TEQIP-III) Project and in part by DST-SERB Startup Research Grant under Award SRG/2019/001122.




[paper] Process Induced Vt Variability

Mandar S. Bhoir, Member, IEEE, Thomas Chiarella, Jerome Mitard, Naoto Horiguchi, Member, IEEE, and Nihar Ranjan Mohapatra, Senior Member, IEEE
Vt Extraction Methodologies Influence Process Induced Vt Variability:
Does This Fact Still Hold for Advanced Technology Nodes? 
IEEE Transactions on Electron Devices, vol. 67, no. 11, pp. 4691-4695, Nov. 2020
DOI: 10.1109/TED.2020.3025750.

Abstract: In this work, we have investigated the influence of Vt extraction procedure on overall Vt variability of sub-10 nm Wfin FinFETs. Using six different Vt extraction techniques (These are 1) constant current (CC) technique, 2) extrapolation in linear regime [ELR, also known as maximum trans-conductance (gm)] technique, 3) trans-conductance extrapolation (TCE) technique, 4) second-derivative (SD) technique, 5) ratio method (RM); and 6) transition method (TM) [1]) we have experimentally demonstrated that the Vt variability is independent of Vt extraction procedure (unlike reported earlier). Furthermore, through systematic evaluation on commonly used Vt extraction techniques, the physics behind this anomalous behavior is investigated. It is shown that the significant variation in metal gate work-function and gate dielectric charges in advanced CMOS nodes is mainly responsible for this behavior. This claim is further validated for FinFETs with deeply scaled fin-width and effective oxide thickness (EOT).


Fig: (a) Schematic illustration of different process-variability sources in FinFET; 
(b)Transfer characteristics for FinFETs with similar Vt, CC but different RSD.
These FinFETs have different Vt, ELR because of RSD induced gm, max variations

Acknowleegement: This work was supported in part by the Visvesvaraya Ph.D. Scheme, MeitY, Government of India MEITY-PHD-250 and in part by the Horizon 2020 ASCENT EU Project (Access to European Nanoelectronics Network) under Project 654384.

References:
[1] A. Ortiz-Conde, F. G. Sánche, J. J. Liou, A. Cerdeira, M. Estrada, and Y. Yue, “A review of recent MOSFET threshold voltage extraction methods,” Microelectron. Rel., vol. 42, no. 4, pp. 583—596, 2002, doi: 10.1016/S0026-2714(02)00027-6

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