Enhanced degradation in polycrystalline silicon thin-film transistors under dynamic hot-carrier stress

We address the mechanisms responsible for the enhanced degradation in the polysilicon thin-film transistors under dynamic hot-carrier stress. Unlike the monotonic decrease of maximum transconductance (G/sub m max/) in static stress, G/sub m max/ in dynamic stress is initially increased due to the channel shortening effect by holes injected into the gate oxide near the drain region and then decreased due to tail states generation at the gate oxide/channel interface and grain boundaries. The threshold voltage variations are dominated by two degradation mechanisms: (1) breaking of weak bonds and (2) breaking of strong bonds to obey the power-time dependence law with a slope of 0.4. The degradation of the sub-threshold slope is attributed to intra-grain bulk states generation.