Enhancement of BTI degradation in pMOSFETs under high-frequency bipolar gate bias

Abstract

Negative bias temperature (NBT) instability of p-MOSFETs with ultrathin SiON gate dielectric has been investigated under various gate bias configurations. The NBT-induced interface trap density (1 it ) under unipolar bias is essentially lower than that under static bias, and is almost independent of the stress frequency up to 10 MHz. On the contrary, 1 it underbipolar pulsed bias of frequency larger than about 10 kHz is significantly enhanced and exhibits a strong frequency dependence, which has faster generation rate and smaller activation energy as compared to other stress configurations. The degradation enhancement is attributed to the energy to be contributed by the recombination of trapped electrons and free holes upon the silicon surface potential reversal from accumulation to inversion.Index Terms-Dynamic stress, negative bias temperature instability (NBTI), pMOSFETs, recombination, ultrathin gate oxide.

Mechanism of Static and Dynamic Bias Temperature Instability in p- and n-MOSFETs

“…∆N it under the dynamic stress is approximately 30% smaller than that under the corresponding static stress. The above predication has been experimentally confirmed in our experiments (29) and in literatures (20,25).…”

“…We also found a reduced and frequency-independent degradation under the unipolar NBT stress (29). However, an opposite behavior was observed in our bipolar bias temperature (BT) experiments compared to that reported in literature: the degradation of pMOSFETs under high-frequency bipolar stress is significantly enhanced and the enhancement is strongly frequency-dependent (29). Moreover, the degradation enhancement is found to be closely related to the fall time (t F ) of the pulse waveform, namely, the time for V g switching from +V a to -V a , while it is almost independent of the rise time (t R ).…”

“…The degradation under the ac stress is frequencyindependent (20,25) or slowly decreases with increasing frequency (23,27). We also found a reduced and frequency-independent degradation under the unipolar NBT stress (29). However, an opposite behavior was observed in our bipolar bias temperature (BT) experiments compared to that reported in literature: the degradation of pMOSFETs under high-frequency bipolar stress is significantly enhanced and the enhancement is strongly frequency-dependent (29).…”

“…Therefore, the degradation enhancement in the stage B is more significant. This effect explains absence of ∆N it enhancement under the unipolar NBT stress and the rapid increase of ∆N it with V hi (29). Fig.…”