| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 94 === There has been a tendency to improve the characteristics of switches in AMLCD (active matrix liquid-crystal display) technology. Particularly, the large photo-induce leakage current is an issue that need to be imminently solved. In this thesis, the amorphous silicon thin film transistors (a-Si:H TFTs) with low photo-induced leakage current will be proposed and studied.
The first, an alternative method has been proposed to suppress photo leakage current of a-Si TFT operated at off-state. We introduce a deep level trap center, made by UV light treatment, into Si film to act as recombination centers. After treating conventional BCE TFTs by UV light, deep traps will be made in active layer by UV light. Experimental results have shown the photo leakage current of devices is lower than that of a-Si TFT without be treated by UV light. Although the mobility is decreased slightly, the degradation of mobility is still tolerable. The mechanism is mainly based on the photo leakage mechanics that deep traps have good ability to recombine electron hole pairs made by back light illuminate.
In addition, a novel a-Si:H TFT structure has been demonstrated to suppress the leakage current under back-light illumination. We will change source and drain metal pads in conventional structure to ITO. Using the heterojunction between ITO and a-Si to reduce photo leakage current. And ITO can be used in conventional island in structure to eliminate schottky leakage current. When under the gate-side illumination, the ITO new structure TFT shows a photo-induced leakage current as low as one order of magnitudes, compared to the conventional a-Si:H TFT device. The superior characteristics of the proposed structure can potentially provide better visual quality for AMLCD products. For that reason, the high performance provides the potential of the proposed a-Si:H TFT to apply for AMLCD and AMOLED technology.
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