An a-Si TFT with a new light-shield structure and its application to active-matrix liquid crystal displays

The authors have observed an increase in off-current in a gate-bottomed inverted-staggered a-Si TFT (thin film transistor) under gate side illumination, despite the prevention of light transmission into the channel region of the a-Si layer by the gate electrode. It was found that the leakage current is generated by irradiating the intrinsic a-Si layer, which protrudes from the gate electrode edge near the drain junction. A novel light-shield structure in which the intrinsic island is placed inside the gate electrode has been developed to reduce the light-induced leakage current. Using this structure and decreasing i-layer thickness to less than 200 nm, and the off-current is maintained at less than 10/sup -10/ A in the negative-gate-voltage region. It has been confirmed that an active-matrix liquid-crystal display using these TFTs has sufficient display performance stability up to 10/sup 5/-lx gateside illumination.<
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