A thermal activation view of low voltage impact ionization in MOSFETs

Abstract

The authors present a thermal activation perspective for direct assessment of the low voltage impact ionization in deep-submicrometer MOSFETs. A comparison of the experimentally determined activation energy and a simple theoretical model is used to demonstrate the underlying mechanism responsible for impact ionization at low drain bias. The study indicates that the main driving force of impact ionization changes from the electric field to the lattice temperature with power-supply scaling below 1.2 V. This transition of driving force results in a linear relationship between log(I/sub SUB//I/sub D/) and V/sub D/ at sub-bandgap drain bias, as predicted by the proposed thermally-assisted impact ionization model.