Impact of Al 2 O 3 Buffer Layer on Ultra-Thin Flexible Polyimide Substrates for Transparent and Flexible InGaZnO Thin Film Transistors

Effects of ALDsgrown Al 2 O 3 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 cm 2 /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 (V on ) 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 V on experienced only a slight negative shift even under the severe bending condition of a curvature radius of 1 mm.