SIMULATION OF LOGARITHMIC TIME-DEPENDENCE OF HOT-CARRIER DEGRADATION IN PMOSFETS

The time dependence of hot carrier degradation in PMOSFETs is simulate d on a 2D device simulator, MEDICI. The degradation is modelled by a s patially uniform negative fixed charge, introduced at the oxide-silico n interface. The effect on the device drain current, threshold voltage and transconductance is studied as a function of the extent and magni tude of the fixed charge. The extent of the fixed charge is identified with the drain extension due to the inversion, by the fixed charge, o f part of the channel adjacent to the drain junction. The drain extens ion is experimentally determined from the gate-to-drain capacitance, w hose stress time dependence therefore gives an indirect time dependenc e for the degradation of other device parameters. Simulation results s how a logarithmic time dependence of degradation in a number of device parameters, confirming earlier experimental observations. Simulation of the electron injection current reveals two peaks, the first one nea r the drain junction and the second one near the edge of the degradati on region. The second peak is considerably weaker and accounts for the progressively longer time needed to create additional degradation.