Evaluation technique for reliability in low-temperature poly-Si thin film transistors

Analysis of the degradation in n-ch TFT under dynamic stress by using pico-second time-resolved emission microscopy was performed. We have successfully detected an emission at the pulse fall edge. Emission intensity increased with decreasing pulse fall time. As the degradation depended on the pulse fall time, this dependence clearly illustrates that hot electrons are the dominant cause of the degradation under dynamic stress. Based on these dependence, we proposed model considering electron traps in poly-Si. Further, we analyzed thermal degradation in low temperature poly-Si thin film transistors by using infrared thermal imaging microscopy. Non uniform distribution was observed in the saturation region along the gate length. The increase of temperature was remarkable at large gate width, therefore, large voltage shift was observed. A universal relationship was obtained, independent of crystallinity of poly-Si. This curve suggests that we should take the degradation of gate oxide such as electron traps into account.