A modified lucky electron model for impact ionization rate in NMOSFET's at 77 K

The nonstationary effects of electrons at 77 K, in the high field saturation region of the MOSFET, are modeled by incorporating an appropriate electron temperature decrease (-/spl Delta/T/sub e/) to the carrier energy, within the framework of a modified lucky electron model. For a thin oxide MOSFET (T/sub cx/=5 nm, L/sub 0/=0.5 /spl mu/m), /spl Delta/T/sub c/ is a function of the electric field in the saturation region, and increases rapidly with drain bias. However, for a thick oxide MOSFET (T/sub cx/=12.5 nm, L/sub g/=5 /spl mu/m), /spl Delta/T/sub e/=280 K is found to adequately describe the impact ionization rate. Our model also explains the crossover of the ionization rates in the thick oxide MOSFET at 77 K and 300 K.