Recoverable and permanent components of VT shift in pulsed NBT stressed p-channel power VDMOSFETs

In this study we investigate NBTI in commercial IRF9520 p-channel VDMOSFETs under both static and pulsed bias stress conditions. The pulsed voltage stressing caused generally lower shifts as compared to static stressing performed at the same temperature with equal stress voltage magnitude, as a consequence of partial recovery during the low level of pulsed gate voltage. Recoverable and permanent components of threshold voltage shift in pulsed negative bias temperature stressed devices are investigated in detail. The existence of characteristic time constant (25 μs), related to a complete removal of the recoverable component of degradation, is clearly shown. Finally, the average value of permanent component of V_T shift induced by a single stress pulse is determined (1.34 × 10^-10 V).