A model of degradation mechanisms in metal-nitride-oxide-semiconductor structures

The degradation of a metal-nitride-oxide-semiconductor (MNOS) structure has been investigated using p-channel MNOS transistors with a relatively thick oxide layer. Significant degradation effects, e.g., a negative shift of the threshold voltage Vth or the flatband voltage VFB, an increase in the density of the SiO2-Si interface states, a deformation of the memory hysteresis curve, and increase in hole conduction in the oxide are observed during positive-bias stress to the gate. Based on these experimental results, a model of degradation mechanisms in the MNOS structure, where hole conduction in the oxide results in the degradation, is proposed.