TIME-DEPENDENCE OF P-MOSFET HOT-CARRIER DEGRADATION MEASURED AND INTERPRETED CONSISTENTLY OVER 10 ORDERS OF MAGNITUDE

Hot-carrier degradation is measured and analyzed over ten orders of magnitude in time for three buried-channel p-MOSFET (p-channel metal-oxide-semicoductor field-effect transistors) types with different oxide thicknesses. We separate the effects of oxide charge and interface states by the charge-pumping technique. Two dominating effects are sufficient to describe the degradation for various gate lengths at many gate and drain voltages consistently over the full time span. First, for worst case degradation, negative oxide charge and interface states are generated by electrons near the drain. This charge is distributed homogeneously over the oxide thickness and it attracts an inversion layer that extends the drain and reduces the effective transistor length logarithmically in time. Simultaneously, this inversion layer prevents substantial degradation related to the interface states, since it masks their effects. A simple model for the logarithmic time dependence is presented. Second, at more negative gate voltages, holes cause interface states that reduce the transconductance with a power-law time dependence, comparable to the worst case n-MOSFET (n-channel MOSFET) degradation. The special initial-stage degradation on short time scales and the influence of other degradation mechanisms is shown to be insignificant in our transistors.