Physical Model of Low-Temperature to Cryogenic Threshold Voltage in MOSFETs

Abstract

This article presents a physical model of the threshold voltage in MOSFETs valid down to 4.2 K. Interface traps close to the band edge modify the saturating temperature behavior of the threshold voltage observed in cryogenic measurements. Dopant freezeout, bandgap widening, and uniformly distributed traps in the bandgap do not change the qualitative behavior of the threshold voltage over temperature. Care should be taken because dopant freezeout results in a different physical definition of the threshold voltage. Using different definitions changes significantly the threshold current level. The proposed model is experimentally validated with measurements in large-area nMOS and pMOS devices of a commercial 28-nm bulk CMOS process down to 4.2 K. Our modeling results suggest that a pMOSspecific phenomenon in the gate stack is responsible for the non-saturating temperature behavior of the threshold voltage in pMOS devices.

Power Performance Analysis of Digital Standard Cells for 28 nm Bulk CMOS at Cryogenic Temperature Using BSIM Models

“…Design requires well calibrated transistor models for low temperature operation, that can be used for circuit level simulations. There have been quite a few attempts to model the behavior of CMOS at low temperatures including but not limited to physics based semiempirical models, simplified-EKV models, virtual source (VS) models etc., [9][10][11][12][13], [23][24][25][26]. There is a need for a physics based, accurate, scalable, robust MOSFET BSIM compatible model for circuit simulation and technology assessment.…”

The functions of a reservoir offset voltage applied to physically defined p-channel Si quantum dots

“…This means that the width of the Si channel is not considered for simplicity. The simulation temperature is chosen to be 300 K because the simulation at low temperatures has the difficulty in convergence 29 – 31 due to the low intrinsic carrier density. Note that our target in the simulation is to grab the trend of the change in the energy band structures and the Fermi level by the reservoir offset voltage, so that the quantitative difference occurred by the different temperatures would not be critical for the conclusion.…”

XQsim

“…(2) Target-temperature extension. We extend CC-Model's temperature coverage by adjusting cryo-MOSFET's three fabrication-related and temperature-dependent MOSFET variables (i.e., carrier mobility [4], saturation velocity [30], and threshold voltage [5]) based on recent cryogenic MOSFET measurement at 4K. In addition, we also extend cryo-wire's resistivity model coverage to 4K range, by adopting previous measurement data from Intel [55] ().…”