Characterization and modelling of Si MOSFETs at liquid helium temperature

A generic analysis of the Si MOSFET operation in the LHT (liquid-helium temperature) range is presented. Analytical models providing current and transconductance transfer characteristics in the linear region and output characteristics in the nonohmic region are proposed. These models rely on a specific mobility law for very low temperature and take into account the effect of source-drain series resistance in both linear and nonlinear regions, which has a drastic influence on the maximum transconductance even for not-too-short channel lengths (L=10 mu m). The influence of carrier velocity saturation at LHT is also considered. A specific parameter extraction method that allows the determination of the main MOSFET parameters is presented. Features of the drain voltage dependence of the mobility at very low longitudinal electric field are pointed out.<>