A Substrate Bias Effect on Recovery of the Threshold Voltage Shift of Amorphous Silicon Thin-Film Transistors

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) were fabricated on a flexible stainless-steel (SS) substrate. The stability of the a-Si:H TFT is a key issue for active matrix organic light-emitting diodes (AMOLEDs). The drain current decreases because of the threshold voltage shift (ΔVTH) during OLED driving. A negative voltage at a floated gate can be induced by a negative substrate bias through a capacitor between the substrate and the gate electrode without additional circuits. The negative voltage biased at the SS substrate can recover ΔVTH and reduced drain current of the driving TFT. The VTH of the TFT increased by 2.3 V under a gate bias of +15 V and a drain bias of +15 V at 65 °C applied for 3,500 s. The VTH decreased by -2.3 V and the drain current recovered 97% of its initial value under a substrate bias of -23 V at 65 °C applied for 3,500 s.