Photosensitivity of InZnO thin-film transistors using a solution process

Abstract

Amorphous silicon (a-Si) and low temperature polysilicon (LTPS) TFTs are extensively used in the flat-panel display industry, but they have a number of disadvantages. Alternatively, oxide semiconductors have been researched for more than a decade as a promising active material for TFTs. Recent electronic devices have been widely utilized with interactive technology to allow interaction with the user. One typical example is interactive display technology combined with a TFT and a sensor. In view of this, oxide semiconductor devices play a role in both switches and photo-sensors in interactive displays. However, most studies of oxide photo-transistors have concentrated on oxide semiconductors made by a vacuum process. During the fabrication of oxide semiconductor devices, the sol-gel solution process used to form an oxide semiconductor has various merits, including its simplicity and low cost as well as its good composition controllability. Here, we present the photosensitivity characteristics of an oxide photo thin-film transistor (TFT) created using the InZnO (IZO) sol-gel process. Upon exposure to light, photocurrent (Iphoto) in the negative gate bias regime is significantly increased with a negligible threshold voltage shift. The photosensitivity is modulated by geometrical factors and by the IZO material composition. We observed a significant effect of the channel thickness and IZO composition on the photosensitivity which was attributed to the screening effect of optically ionized oxygen vacancies (Vo++). Particularly, the optimized bi-layered oxide photo-TFT presents a good Iphoto/Idark photosensitivity value of 3x104 and a subthreshold slope of 0.96V/decade. In addition, the persistent photoconductivity of the oxide photo-TFT was removed by applying positive gate voltage, resulting in good high-speed operation. These results taken together demonstrate that the IZO photo-TFT produced by the sol-gel process can be successfully when applied to interactive displays.