Effect of an Al2O3/TiO2 Passivation Layer on the Performance of Amorphous Zinc–Tin Oxide Thin-Film Transistors

The effect of an Al2O3/TiO2 stacked passivation layer on the performance of amorphous ZnSnO (a-ZTO) thin-film transistors (TFTs) was investigated by comparing field-effect mobility (μFE) and subthreshold swing after passivation layer deposition. The values observed were 4.7 cm2/Vs and 0.64 V/decade, respectively, for uncoated TFTs and 4.6 cm2/Vs and 0.62 V/decade for passivated TFTs. In addition, excellent water vapor transmission was observed for electron beam-irradiated Al2O3/TiO2-passivated poly(ether sulfone) substrates in a humidity test, because the Al2O3/TiO2 passivation layer can enhance the interface properties between Al2O3 and TiO2. To investigate the origin of this enhancement, we performed x-ray photoelectron spectroscopy of both unpassivated and Al2O3/TiO2-passivated TFTs with a-ZTO back-channel layers after Ar annealing.