Consideration of feed-through voltage in amorphous-Si TFT's

Feedthrough voltage is an important factor in designing integrated data drive circuits and display area in thin-film-transistor liquid-crystal displays (TFT LCDs). With respect to feedthrough voltage, only the gate-source overlay capacitance has been considered in amorphous-Si (a-Si) TFTs, because of their staggered structure with overlap area. It is pointed out that, in a-Si TFTs designed as active elements, feedthrough voltage is mainly due to the carrier redistribution. The main reason is that, since the field-effect mobility is low (W/L>1), the leakage current must be kept low (L>or=10 mu m), and an active layer is inserted in the overlap area (unlike the case with MOS device structures), the area of the active layer is large. Taking the carrier redistribution into account, the maximum difference between the voltage obtained using the modified model and the experimental voltage is within 20%. By comparison, the results obtained using the previous model for TFTs are approximately three times smaller than the experimental results.>