Stability improvements of InGaZnO thin-film transistors on polyimide substrates with Al^sub 2^O^sub 3^ buffer layer

We investigate the effects of atomic layer deposition (ALD)-grown Al2O3 buffer layer on the device characteristics of flexible amorphous InGaZnO thin-film transistors (TFTs) fabricated on ultrathin polyimide (PI) films. The TFT with a buffer layer exhibited a saturation mobility of 8.6 cm2 V−1 s−1 and a subthreshold swing of 0.16 V dec−1 after annealing at 150 °C. Under negative bias temperature stress at 40 °C, the turn-on voltage instabilities of TFTs with and without the buffer layer were estimated to be −1.0 and −13.2 V, respectively. This marked difference is mainly due to the adsorption of water molecules on the PI film resulting in a positively charged surface.