A Modified Lucky Electron Model for Impact lonization Rate in NMOSFET's at 77 K

Abstract

The nonstationary effects of electrons at 77 K, in the highfield saturation region of the MOSFET, are modeled by incorporating an appropriate electron temperature decrease (-ATe) to the carrier energy, within the framework of a modified lucky electron model. For a thin oxide MOSFET (Tox = 5 nm, Lg = 0.5 μm), ATe is a function of the electric field in the saturation region, and increases rapidly with drain bias. However, for a thick oxide MOSFET (Tox = 12.5 nm, Lg = 5 μm), ATe = 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. © 1999 IEEE.