High- PFET DC Hot-Carrier Mechanism and Its Relation to AC Degradation

Recently, negative bias temperature instability (NBTI) enhanced by local self-heating has been proposed as a mechanism for high-V_g PFET ??hot-carrier?? degradation. This is based on the idea that the effective temperature for NBTI is increased in the drain region due to a very localized self-heating effect reported in the literature by Pop and others. Our PFET dc stress data are consistent with local self-heating activated NBTI at high V_g , but at mid V_g, we observed similar behavior to typical NFET hot carriers, i.e., energy-driven hot carrier (EDHC). If self-heating is involved with the PFET high-V_g dc degradation, the question of ac behavior naturally arises. Our PFET ring-oscillator stress results demonstrate that the high-V_GS PFET hot carrier dominant under dc stress does not significantly contribute under typical CMOS switching conditions, whereas the mid-V_GS hot carrier does. This supports the idea that the predominant damage mechanism involved at high V_GS is NBTI enhanced by local self-heating with a thermal time constant longer than a few hundred picoseconds.