Suppressed Degradation of Elevated-Metal Metal-Oxide Thin-Film Transistors Under Bipolar Gate Pulse Stress

In this letter, investigations on the reliability of elevated-metal metal-oxide (EMMO) thin-film transistors (TFTs) under bipolar gate pulse stress are reported. Different from conventional amorphous indium-gallium-zinc oxide TFTs, EMMO TFTs exhibit negligible dynamic degradation during the pulse transitions and the device degradation is dominated by the DC mechanism. Though negative threshold voltage (V-th) shift is observed under both positive bias stress (PBS) and negative bias stress, the Vth shift caused by the bipolar pulse stress is smaller than that induced by the PBS with the same positive gate bias as in the bipolar gate pulse and the same effective PBS time, where the Vth shift introduced during the positive bias stage in the bipolar pulse stress is believed to be partially recovered during the negative bias stage. These degradation phenomena are proposed to be due to the improved quality of the channel and the gate oxide with the oxidizing thermal heat-treatment during the fabrication of EMMO TFTs, which eventually lead to a reliable performance for the EMMO TFTs under bipolar gate pulse stress.