Effect of Dynamic Bias Stress in Short-Channel (L=1.5 µm) p-Type Polycrystalline Silicon Thin-Film Transistors

Abstract

We have investigated the stability of short-channel (1.5 µm) p-type polycrystalline silicon (poly-Si) thin film transistors (TFTs) under AC bias stress. The threshold voltage of the short-channel (L=1.5 µm) poly-Si TFT was increased by about -7.44 V after AC bias stress, whereas the threshold voltage of the long-channel poly-Si TFT was relatively stable. A two-step degradation process was also observed. In the first step, the threshold voltage of short-channel poly-Si TFTs underwent a consistent positive shift for 100 s. In contrast, the threshold voltage started to undergo a negative shift when accompanied by significant degradation in the subthreshold region. This negative shift of threshold voltage and the significantly degraded subthreshold swing value in the short-channel TFT under dynamic stress may be mainly due to the generation of stress-induced deep- and shallow-level trapping states near the drain junction.