Enhanced electrical stability of thin film transistors based on nanocrystalline silicon films

In this work, nanocrystalline silicon (nc-Si) films were achieved by using normally processing method of amorphous silica thin film transistors (a-Si TFTs), plasma enhanced chemical vapor deposition (PECVD). The effects of PECVD process parameters on the crystallization rate of nc-Si films were comprehensively studied and then an optimized nc-Si film has been achieved with a crystallinity of 50.87%. The electrical properties and stability of nc-Si TFTs are further investigated and compared with a-Si TFTs. The Delta V (th) of the nc-Si TFTs are 0.14 V and -3.32 V under positive bias-temperature-illumination stress (60 degrees C, 30 V, 6000 nit) and negative bias-temperature-illumination stress (60 degrees C, -30 V, 6000 nit) after 1 h, which are 1.96 V and -5.51 V for a-Si TFT, respectively. The result reveals better photo stability of nc-Si TFTs than a-Si TFTs which is attributed to fewer defect states in nc-Si films.