Deep-depletion-layer impact-ionization-induced gate-oxide breakdown in thin-oxide n-MOSFETs

Abstract

This work extensively examines gate-oxide breakdown behaviours of n-MOSFETs by means of enhancement-type and depletion-type devices with various channel dimensions under different operation conditions. The results indicate that positive-charge accumulation in gate oxide is only one of the processes occurring during high-field stress but is not the main cause for gate-oxide breakdown. The accelerated gate-oxide breakdown in MOSFETs is initiated by interface states at the Si-SiO2 interface, which are generated from the following process: holes created by impact ionization in the deep-depletion layer of the drain are injected into the gate oxide and trapped near the Si-SiO2 interface; then they recombine with hot electrons crossing the interface. In addition, gate-oxide breakdown at the gate-and-drain overlap may lead to that between gate and source.