[paper] Model for Cryo-CMOS Subthreshold Swing

Arnout Beckers, Jakob Michl, Alexander Grill, Member IEEE; Ben Kaczer, Marie Garcia Bardon, Bertrand Parvais, Bogdan Govoreanu, Kristiaan De Greve, Gaspard Hiblot, 

and Geert Hellings, Senior Member IEEE

Physics-Based and Closed-Form Model for Cryo-CMOS Subthreshold Swing

in IEEE Transactions on Nanotechnology, vol. 22, pp. 590-596, 2023,

DOI 10.1109/TNANO.2023.3314811.

IMEC, Leuven (B)

Institute for Microelectronics, TU Vienna (A)

Vrije Universiteit Brussel (B)

KU Leuven (B)

Abstract: Cryogenic semiconductor device models are essential in designing control systems for quantum devices and in benchmarking the benefits of cryogenic cooling for high-performance computing. In particular, the saturation of subthreshold swing due to band tails is an important phenomenon to include in low-temperature analytical MOSFET models, as it predicts theoretical lower bounds on the leakage power and supply voltage in tailored cryogenic CMOS technologies with tuned threshold voltages. Previous physics-based modeling required to evaluate functions with no closed-form solutions, defeating the purpose of fast and efficient model evaluation. Thus far, only the empirically proposed expressions are in closed form. This article bridges this gap by deriving a physics-based and closed-form model for the full saturating trend of the subthreshold swing from room down to low temperature. The proposed model is compared against experimental data taken on some long and short devices from a commercial 28-nm bulk CMOS technology down to 4.2 K.

FIG: (a) TEM picture of a mature imec technology node. (b) Electrostatic potential fluctuations near the channel/oxide interface. (c) Gaussian distributed depths of the potential wells. (d) Including the binding energy in the wells in the quantum picture gives a Laplace distribution of P(Eb). (e-f) Convolution (*) of P(Eb) with the sharp-edged 2-D DOS leads to a logistic/Fermi-like DOS function with an exponential tail.

[chapter] Near-Threshold Digital Circuits for Nearly-Minimum Energy Processing

Near-Threshold Digital Circuits for Nearly-Minimum Energy Processing

Massimo Alioto

Department of Electrical & Computer Engineering, National University of Singapore

in Enabling the Internet of Things; pp 95-148 

DOI: 10.1007/978-3-319-51482-6_4

This chapter addresses the challenges and the opportunities to perform computation with nearly-minimum energy consumption through the adoption of logic circuits operating at near-threshold voltages. Simple models are provided to gain an insight into the fundamental design tradeoffs. A wide set of design techniques is presented to preserve the nearly-minimum energy feature in spite of the fundamental challenges in terms of performance, leakage and variations. Emphasis is given on debunking the incorrect assumptions that stem from traditional low-power common wisdom at above-threshold voltages. The traditional EKV model is very useful for quick estimates, but it oversimplifies the IV characteristics that is observed in actual nanometer CMOS technologies [read more...]

[paper] Electronically tunable MOSFET-based resistor

Electronically tunable MOSFET-based resistor used in a variable gain amplifier or filter

W. L. Tan, C. H. Chang and L. Siek

Nanyang Technological University; Singapore 

2016 International Symposium on Integrated Circuits (ISIC), Singapore, 2016, pp. 1-4.

doi: 10.1109/ISICIR.2016.7829715

Abstract: We present a new design of an electronically tunable linear MOS resistor circuit that operates in the subthreshold saturation region, supported with mathematical derivations and simulation results using CSM0.13µm technology. For a given potential difference across the MOS resistor, its gate voltage will be automatically biased through feedback to provide the correct amount of current based on the desired resistance set through the bias current. Equating the output current of the OTA with the subthreshold equation of the EKV model. In comparison with an existing design, the proposed design offers equal tunabilty with 36 less transistors for unidirectional current and 28 less transistors with one more bias current transistor for bidirectional current. A bias current ranging between 10nA to 100nA offers a tunable linear resistance between 20MΩ to 140MΩ [read more...]