Photosensitivity of Amorphous InGaZnO Thin-Film Transistors
T. C. (Richard) Fung, C. S. (Patrick) Chuang, Kenji Nomura, B.G. Mullins and Jerzy Kanicki
Over last several years, there has been a great interest in thin-film transistors (TFT) made of transparent amorphous InGaZnO4 (a-IGZO) semiconductors. This is mainly due to its unique advantages such as visible light transparency, large-area uniform deposition at low temperature, and high carrier mobility. These attractive properties can potentially overcome all the drawbacks currently existed in conventional amorphous or polycrystalline silicon TFT technology used for active-matrix flat panel displays (AM-FPDs). In this project, we studied the photosensitivity of a-IGZO TFT and evaluated its feasibility for AM-FPDs.
We have fabricated inverted staggered a-IGZO TFTs and measured their electrical properties under monochromatic illumination. The a-IGZO TFTs used in this work have the following dark electrical properties: threshold voltage of 2.57V, field-effect mobility ranging from 3 to 8 cm2V-1s-1 for different channel width/length, subthreshold swing of 0.27V/decade and on/off current over 108. During the a-IGZO TFTs illumination with the wavelengths ranging from 460 to 660 nm, the off-state drain current only slightly increases while a large increase was observed for the wavelength below 400 nm. Threshold voltage and subthreshold swing are also only slightly modified between 460 to 660 nm, while field-effect mobility is almost unchanged in the investigated photo energy range.
The observed results are consistent with the a-IGZO optical energy band gap of about 3.05 eV. Our study suggests that the a-IGZO TFTs are light sensitive only above 3.0 eV and it suitable for a stable operation in AM-FPDs. This project is partially supported by DARPA and Applied Materials Corporation.
