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

TL;DR

This paper introduces a physics-based, closed-form model for the subthreshold swing in cryogenic CMOS devices, enabling fast and accurate predictions of device behavior at low temperatures relevant for quantum computing and high-performance applications.

Contribution

It derives a novel closed-form analytical model for the subthreshold swing saturation trend from room temperature to cryogenic temperatures, improving upon previous empirical models.

Findings

Model accurately fits experimental data from 28-nm CMOS devices at 4.2 K.

Captures the full saturating trend of subthreshold swing at cryogenic temperatures.

Provides a practical tool for device design and benchmarking in cryogenic electronics.

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.