MOSFET parameter degradation after Fowler–Nordheim injection stress

We have investigated the degradation of tunnel oxides due to Fowler-Nordheim electron injection from polysilicon gate. Tested devices are n-MOSFET normally used for Flash EPROM applications with four different technologies for the tunnel oxide layer. Stresses have been performed at different source and drain bias conditions for a total injected charge up to 1 C/cm(2). The oxide characteristics and degradation have been determined comparing the MOSFET threshold voltage and transconductance peak for as received devices and after each stress step.