The mechanisms of on/off currents for the dual-gate a-Si:H thin film transistors with various length sizes of indium-tin-oxide top gate

Two types of dual-gate a-Si:H TFTs with four different sizes of transparent indium-tin-oxide (ITO) top gate length have been made for the static characteristics investigation. With various sizes of ITO top gate length, we clearly identify that the various on currents for the dual-gate TFTs with dual-gate driving are due to the high resistance of the parasitic intrinsic a-Si:H regions between the back electron channel and the source/drain contact. For the off state of the dual-gate TFTs, the Poole-Frenkel effect is also enhanced due to the back channel accumulation holes in the vicinity to the source/drain contact. Furthermore, we first observe that the dual-gate driving a-Si:H TFTs exhibit extremely low photo-leakage currents during a certain range of negative gate voltages under illumination. The high on-off current ratio under backside illumination makes the dual-gate TFTs the suitable devices as the switching elements in liquid crystal display (LCD) or other applications.