The improvement and copper contamination of TFTs in active-matrix liquid-crystal displays (AMLCDs) will be discussed in this thesis. TFT with hydrogenated microcrystalline silicon films (mc-Si:H) came to be the attractive candidate due to its higher mobility and stable characteristics. We deposited mc-Si:H films by inductively coupled plasma chemical vapor deposition system (ICPCVD) to achieve fast deposition rate (4~5 Å /sec) which is faster than the conventional PECVD (around 0.1~1 Å/sec). The crystallization of mc-Si:H films deposited by ICPCVD at low temperature was explained by hydrogen etching model. With modulating the hydrogen dilution and rf power of ICPCVD, we can determine the crystallinity of silicon films. Two ways to increase the crystallinity of silicon films was designed: one is the plasma treatment on surface of substrate, and the other is on seed layer. Both methods increased the crystallinity of silicon films and were explained by hydrogen etching and influence of roughness surface. Besides, we discuss the effects of substrate temperature in crystallinity. Microcrystalline silicon films can be deposited at very low temperature as 250¢J, where we may deposit microcrystalline silicon films on flexible plastics substrate in the future. Additionally, we investigated the effects of copper contamination on active layer of TFTs. High resolution large-area AMLCDs will take copper gate and connection to replace aluminum for lowering the RC decay of aluminum connection. We observed that the mobility and output characteristics of TFTs were decreased with copper contamination which played as traps in the channel of TFTs. Besides, part copper contamination at the surface of a-Si layer would form the chemical oxide and eliminate surface state of channel. Therefore, the off current will be decreased.