Transient hot-electron effect on n-channel device degradation (MOSFETs)

Hot-electron degradation mechanisms under AC stress using a pulsed gate and DC drain bias condition are investigated. The rate of device decay is monitored as a function of the gate pulse transient period. Simulation results reveal that during a fast turn-off transient, the electron concentration and electric field in the drain region are higher than their corresponding DC values, resulting in an increase in the peak substrate current. This, along with experimental data, shows these transient excess carriers to be responsible for the enhancement of device degradation under the described stress. The enhancement factor of the degradation is a function of the gate pulse transient time. Comparison between the analysis based on DC measurement and calculations based on transient simulation are shown. Better agreement with experimental data is obtained by using the transient analysis. The correlation between AC and DC stress data is also shown based on the impact ionization model.<>