Thin film transistors based on solution-processed In2O3:W. A remarkably stable semiconductor under high negative bias stress

Abstract

A wide range of metal oxide-based semiconductors namely Indium Zinc Oxide and Indium Gallium Zinc Oxide have extensively been implemented in thin film transistors (TFTs) mainly for applications in displays. The large amount of deep defect states in Indium Zinc Oxide that are attributed to oxygen deficiency states result in TFTs instability as repeatedly reported. To tackle this issue, the inclusion of gallium has been proposed in order the oxygen deficiency states density to be reduced. It’s been evidenced however that gallium inclusion promotes device photosensitivity to visible light, an undesirable effect for applications in flat panel displays. To that end, and in order the aforementioned stability issues to be addressed we have investigated solution-processed tungsten-doped crystalline Indium Oxide (In2O3:W) as a function of the W content. In2O3:W thin films were deposited by spray coating at 350 oC in air from InCl3 and WCl5 blends in methanol and their physical properties were identified by UV-Vis absorption spectroscopy, FTIR, X-ray diffraction, AFM, and field effect measurements. For optimal deposition conditions in terms of W content, TFTs employing solution processed Al2O3 gate dielectrics, In2O3:W semiconducting channels and gold source and drain contacts underwent negative bias stress for 6000 s, and showed excellent stability characteristics such as a small change of the threshold voltage (in the range between 2 V and 2.3 V) without significantly decreasing the electron mobility, which slightly decreased from 16 to 14 cm2/Vs