Photo-leakage current of poly-Si thin film transistors with offset and lightly doped drain structure

The suppression of photo-leakage current (I-photo) has been an important issue in the fabrication of high-brightness liquid-crystal projectors. We have investigated the generation mechanism of I-photo in poly-Si thin film transistors (TFTs) with an offset structure. It is found that I-photo is mainly generated at the offset legion and the decrease in the offset length is important to suppress I-photo This is because the electric field is applied to the offset region and carriers, generated in the region, can be extracted. We have realized an offset poly-Si TFT with both high mobility and low I-photo by decreasing the offset length to 0.5 mu m with the lateral etching method.