A comprehensive study of hot carrier stress-induced drain leakage current degradation in thin-oxide n-MOSFET's

Abstract

The mechanisms and characteristics of hot carrier stress-induced drain leakage current degradation in thin-oxide n-MOSFET's are investigated. Both interface trap and oxide charge effects are analyzed. Various drain leakage current components at zero V-gs such as drain-to-source subthreshold leakage, band-to-band tunneling current, and interface trap-induced leakage are taken into account, The trap-assisted drain leakage mechanisms include charge sequential tunneling current, thermionic-field emission current,:and Shockley-Read-Hall generation current. The dependence of drain leakage current on supply voltage, temperature, and oxide thickness is characterized. Our result shows that the trap-assisted leakage may become a dominant drain leakage mechanism as supply voltage is reduced. In addition, a strong oxide thickness dependence of drain leakage degradation is observed. In ultra-thin gate oxide (30 Angstrom) n-MOSFET's, drain leakage current degradation is attributed mostly to interface trap creation, while in thicker oxide (53 Angstrom) devices, the drain leakage current exhibits two-stage degradation, a power law degradation rate in the initial stage due to interface trap generation, followed by an accelerated degradation rate in the second stage caused by oxide charge creation.