High-$V_{\rm GS}$ 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-$V_{\rm GS}$ PFET hot carrier dominant under dc stress does not significantly contribute under typical CMOS switching conditions, whereas the mid-$V_{\rm GS}$ hot carrier does. This supports the idea that the predominant damage mechanism involved at high $V_{\rm GS}$ is NBTI enhanced by local self-heating with a thermal time constant longer than a few hundred picoseconds.