PHYSICAL MODELS FOR DEGRADATION EFFECTS IN POLYSILICON THIN-FILM TRANSISTORS

In this paper we present experimental data showing the degradation in performance of polysilicon Thin-Film Transistors (TFT's) under a variety of bias stress conditions. We propose a model to explain these degradation effects whereby device performance degrades due to changes in the effective density of defect states in the material. Unlike single-crystal devices which degrade from hot-carrier effects, we believe that poly-Si TFT's degrade primarily due to the presence of high carrier densities in the channel. We present good agreement between our computer simulations of the device characteristics and experimental data. Finally, we show that stressing under transient conditions leads to a more severe performance degradation than stressing under comparable steady-state conditions.