High-$V_{\rm GS}$ PFET DC Hot-Carrier Mechanism and Its Relation to AC Degradation

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Recently, negative bias temperature instability (NBTI) enhanced by local self-heating has been proposed as a mechanism for high-<formula formulatype="inline"><tex Notation="TeX">$V_{g}$</tex></formula> 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 <formula formulatype="inline"><tex Notation="TeX">$V_{g}$</tex></formula> , but at mid <formula formulatype="inline"><tex Notation="TeX">$V_{g}$</tex></formula>, 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- <formula formulatype="inline"><tex Notation="TeX">$V_{g}$</tex></formula> dc degradation, the question of ac behavior naturally arises. Our PFET ring-oscillator stress results demonstrate that the high-<formula formulatype="inline"><tex Notation="TeX">$V_{\rm GS}$</tex></formula> PFET hot carrier dominant under dc stress does not significantly contribute under typical CMOS switching conditions, whereas the mid-<formula formulatype="inline"><tex Notation="TeX">$V_{\rm GS}$</tex></formula> hot carrier does. This supports the idea that the predominant damage mechanism involved at high <formula formulatype="inline"> <tex Notation="TeX">$V_{\rm GS}$</tex></formula> is NBTI enhanced by local self-heating with a thermal time constant longer than a few hundred picoseconds. </para>