Operational stability of solution-processed indium-oxide thin-film transistors: Environmental condition and electrical stress

We investigate the operational stability of bottom-gate/top-contact-structured indium-oxide (In₂O₃) thin-film transistors (TFTs) in atmospheric air and under vacuum. Based on the thermogravimetric analysis of the In₂O₃ precursor solution, we utilize a thermal annealing process at 400 °C for 40 min to prepare the In₂O₃ films. The results of X-ray photoemission spectroscopy and field-emission scanning electron microscopy show that the electron is the majority carrier in the In₂O₃ semiconductor film prepared by a spin-coating method and that the film has a polycrystalline morphology with grain boundaries. The fabricated In₂O₃ TFTs operate in an n-type enhancement mode. When constant drain and gate voltages are applied, these TFTs in atmospheric air exhibit a more acute decay in the drain currents with time compared to that observed under vacuum. In the positive gate-bias stress experiments, a decrease in the field-effect mobility and a positive shift in the threshold voltage are invariably observed both in atmospheric air and under vacuum, but such characteristic variations are also found to be more pronounced for the atmospheric-air case. These results are explained in terms of the electron-trapping phenomenon at the grain boundaries in the In₂O₃ semiconductor, as well as the electrostatic interactions between electrons and polar water molecules.