Hot Carrier Instability Mechanism in Accumulation-Mode Normally-off SOI nMOSFETs and Their Reliability Advantage

Abstract

This work studies the degradation mechanism of the hot carrier instability in normally-off Accumulatin-Mode SOI nMOSFETs. From the experimental examination of degradations in transistor- transfer characteristics and low frequency noise level at various transistor operation bias regions, it is proposed that the major degradation in the Accumulation-Mode nMOSFETs is the positive charge and interface state generations at the front gate insulator/Si interface at the Drain side due to the injection of hot holes that are generated by impact ionizations caused by channel hot electrons. It is experimentally shown that the Accumulation-Mode nMOSFETs have higher hot carrier immunity than the Inversion-Mode FD-SOI nMOSFETs. Also, effects of the hot carrier stress to the transistor-transfer characteristics are shown to be smaller for devices with higher dopant concentration of SOI layer (NSOI), which originates from the smaller influence of the quality of the front gate insulator/Si interface to the current drivability in higher NSOI devices.