The Mysterious Bipolar Bias Temperature Stress from the Perspective of Gate-Sided Hydrogen Release

While the bias temperature instability has provided many puzzles for more than half a century, the observation that bipolar (+Vg/-Vg) AC stress can lead to larger degradation than DC or unipolar (Vg/0) AC NBTI/PBTI combined, is particularly mysterious. Interestingly, similar observations have been made for oxide breakdown and hot carrier injection. Both have been linked to accelerated hydrogen release from the oxide under alternating positive and negative bias which then causes the creation of near-interface states. Based on these observations, we investigate the phenomenon from the perspective of the recently proposed gate-sided hydrogen release model for BTI. We suggest a mechanism which can explain the accelerated degradation observed during bipolar AC stress and investigate and validate possibilities for mitigating the effect by reducing the oxide volume from which H is released.