Impact of Al2O3 Buffer Layer on Ultra-Thin Flexible Polyimide Substrates for Transparent and Flexible InGaZnO Thin Film Transistors

Effects of ALDsgrown Al2O3 buffer layer on the device characteristics of the flexible amorphous InGaZnO (IGZO) thin film transistors (TFTs) fabricated on ultra-thin polyimide films were investigated. The TFT with a buffer layer exhibited a saturation mobility of 8.6 cm2/Vs and a subthreshold swing of 0.16 V/dec, which was superior to those of the TFT without a buffer layer. Furthermore, under negative bias temperature stress, the turn-on voltage (Von) instabilities for the TFTs with and without the buffer layer were estimated to be −1.0 and −13.2 V, respectively, owing to the adsorption of water molecules on the PI surface resulting in positively-charged surface. Flexibility of the fabricated IGZO TFT was also evaluated. The Von experienced only a slight negative shift even under the severe bending condition of a curvature radius of 1 mm.