Hot-carrier NMOST degradation at periodic drain signal

Hot-carrier-induced NMOST degradation is considered for periodic drain-source signal. A general lifetime relationship is derived on the basis of quasi-static approximation and a lifetime model for DC condition. Two practical cases are discussed: sinusoidal drain signal from 0V to V/sub DD/ (circuit supply) and trapezoidal signal from 0V to V/sub DD/ (in special case, it reduces to triangular waveform). Compact, practically useful, formulas are proposed. The model for AC conditions is based on the same physical approximations that are traditionally used in the derivation of physically crude, but well applicable lifetime models in DC conditions. A strategy is proposed for building-in HC-reliability of NMOSFET subjected to a periodic large drain-signals in analog circuits.