NBT stress-induced degradation and lifetime estimation in p-channel power VDMOSFETs

Threshold voltage shifts found in commercial p-channel power VDMOSFETs during the NBT stressing are fitted using stretched exponential equation in order to estimate the device lifetime, as well as to discuss the impacts of stress conditions, choice of extrapolation parameters, and extrapolation model. Excellent agreement between the stretched exponential fit and experimental data found in later stress phases allows for an accurate estimation of device lifetime for the lowest stress voltage applied, which justifies the use of stretched exponential or some other suitable fit. The realistic failure criterion for devices and experimental conditions used in our study is found to fall in the 100–150 mV range. The lifetime estimates are found to strongly depend on the model used for extrapolation to normal operating conditions. The 1/VG model is shown to provide much faster output since it appears to allow the use of higher stress voltages while still yielding rather accurate lifetime estimates.