Flat-panel Display China-africa Crystal Silicon Thin Film Transistor Leakage Current Nature Of The Study To Improve

As the core device of LCD module, TFT array is always focused on by both industry engineers and science. Amorphous silicon is the major material for TFT because of its low cost and matured process flow. It is very practical to improve the performance of a-Si:H TFT. As the pixel pitch getting smaller, the leakage current of a-Si:H TFT has become a big problem constraining the performance of LCD. The leakage current characteristic of a-Si:H TFT and the way to improve are investigated in this thesis.Basic TFT-LCD driving principle and physics of amorphous silicon device are reviewed first. After that, the mechanism of leakage current is studied at physics model level. Three leakage mechanisms, i.e., channel charge emission, back channel effect and Poole-frenkel effect hole current are reviewed. The current model discloses that the key factors of leakage current are the density of localized states at back channel interface and front channel interface, the electric field between source/drain and gate.Based on the physics model of leakage current, a set of experiments are proposed Process parameters such as film thickness and quality, Hydro-treatment after dry etching, N+doping are adjusted in order to verify the mechanisms. The result showed that graded N+doping process can effectively suppress poole-frenkel effect leakage current, which is consistent with the theory analysis.Another set of experiments are proposed with N+graded as the baseline. Parameters such as PECVD rf-Power, low power film thickness and the silane hydrogen ratio are adjusted. After that, the off-state current, on-state current and mobility are analyzed quantitatively. Among the experiment conditions, one condition showed low leakage current, which is lower than the original one by59%, good on-state current and uniformity. The improve method is effective and provide a way to decrease leakage current in mass production.