Optimization of Sputtering Parameters and Their Effect on Structural and Electrical Properties of CAAC-IGZO Thin-Film Transistors

A c-axis aligned crystalline indium gallium zinc oxide (CAAC-IGZO) possesses unique properties beneficial for thin-film transistors (TFTs). In this study, we investigate the effect of oxygen ratio and radio frequency (RF) power on the structural, electrical, and operational characteristics of CAAC-IGZO thin films. Films were deposited on SiO2 substrates using an RF sputtering system equipped with a target containing In, Ga, Zn, and O with a composition ratio of 1:1:1:4. The effect of oxygen percentage on the structural characteristics was analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM). The oxygen percentage in the film was found to play a crucial role in forming the CAAC-IGZO and orientation of the thin films. With increasing O2 fraction, the (009)-preferred orientation of the films improved. X-ray absorption spectroscopy also validated the improved orientations of the CAAC-IGZO with high O2 concentrations up to 70%. In terms of TFT performance, however, the device with 3.3% oxygen exhibited the best performance with a saturation mobility of 10.9 cm2 V- 1 s- 1. TFT devices were prepared at a low oxygen fraction (10%) with different RF power inputs from 100 to 250 W, where the device prepared with highest power (250 W) showed the best performance.