Channel composition effect on the bias-illumination-stress stability of solution-processed transparent oxide thin-film transistors using amorphous aluminum-indium-zinc-oxide channel layers

Channel composition effect on the device stabilities of In-Zn-O (IZO) and Al-In-Zn-O (AIZO) thin-film transistors (TFTs) were investigated under negative gate bias illumination stress (NBIS) conditions. The fabricated TFTs with a top-gate bottom-contact structure did not show any marked shifts of threshold voltage (ΔV _th) under positive and negative bias stress for 104 s thanks to the self-passivation effect. While the channel composition effect was negligible under the bias stress conditions without any illumination, there were distinct variations in NBIS instabilities for the AIZO TFTs with various compositions. The value of ΔV _th of the IZO TFT was suppressed by incorporating Al from 2.44 to 1.82 V under the NBIS at blue wavelength. The increase in In composition was confirmed to enhance the carrier mobility but deteriorate the NBIS stability. The AIZO TFT with a In/Zn ratio of 3/7 and an incorporated Al of 5 mol% exhibited the best device characteristics among the fabricated devices, in which the μsat, SS, on/off ratio were estimated to be approximately 0.58 cm² V^-1 S^-1, 0.25 V/dec, and 3.5 × 10⁷, respectively. However, the value of ΔV _th was 6.39 V under the blue NBIS conditions. These composition dependent NBIS instabilities mainly originated from the photo-induced excitation from [_o] to [_o ²⁺].