Analysis of recoverable and permanent components of threshold voltage shift in NBT stressed p-channel power VDMOSFET

In this study we investigate the dynamic recovery effects in IRF9520 commercial p-channel power vertical double diffused metal–oxide semiconductor field-effect transistors (VDMOSFETs) subjected to negative bias temperature (NBT) stressing under the particular pulsed bias. Particular values of the pulsed stress voltage frequency and duty cycle are chosen in order to analyze the recoverable and permanent components of stress-induced threshold voltage shift in detail. The results are discussed in terms of the mechanisms responsible for buildup of oxide charge and interface traps. The partial recovery during the low level of pulsed gate voltage is ascribed to the removal of recoverable component of degradation, i.e., to passivation/neutralization of shallow oxide traps that are not transformed into the deeper traps (permanent component). Considering the value of characteristic time constant associated with complete removal of the recoverable component of degradation, it is shown that by selecting an appropriate combination of the frequency and duty cycle, the threshold voltage shifts induced under the pulsed negative bias temperature stress conditions can be significantly reduced, which may be utilized for improving the device lifetime in real application circuits. (paper)