| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Yongjin Im, Pusan National University, Republic of Korea |
| Authors: | Y.J. Im, Pusan National University, Republic of Korea J.H. Shin, Pusan National University, Republic of Korea S.J. Kim, Pusan National University, Republic of Korea S.S. Ha, Pusan National University, Republic of Korea C.H. Park, Pusan National University, Republic of Korea M.S. Yi, Pusan National University, Republic of Korea |
| Correspondent: | Click to Email |
We fabricated amorphous oxide semiconductor thin-film transistors (TFTs) using GeO2-doped InZnO (Ge-IZO) thin films as active-channel layers. The Ge-IZO thin films were deposited at room temperature by radio-frequency (RF) magnetron co-sputtering, and then annealed in air for 1 h at 300°C. Some processing parameters such as sputtering oxygen partial pressure [O2/(Ar + O2)] and sputtering power for GeO2 target were changed to investigate what was the optimal amount of Ge in the Ge-IZO active layer.
The cross-sectional schematic of Ge-IZO TFT and a FE-SEM image of Ge-IZO thin film studied in this paper are shown in Fig. 1, and the electrical performance of Ge-IZO TFT is compared with IZO TFT in Fig. 2.
A small concentration of Ge added to IZO by co-sputtering with less than 5W of GeO2 target power enhanced the saturation mobility μsat. The decrease of μsat at high power of GeO2 target in Fig. 2 was caused by the increased disorder in case of the high power of GeO2 target. Threshold voltages (Vth) in Fig. 2 increases with increase in GeO2 target power until 20W; thereafter, it decreases. This result should be inversely related to the carrier concentration, which indicates that a small concentration of Ge can lead to retention of its strong bonding with oxygen, thereby suppressing the excessive oxygen vacancies. This is the reason why Vth increases. Higher Ge-concentration can lead to the greater disorder and this explains why Vth decreases with increase in Ge concentration.
The device performance was better when low concentration of Ge is incorporated to IZO than with pure IZO or high Ge concentration. In order to optimize the electrical properties of Ge-IZO TFTs, we tried to adjust the processing parameters and the best Ge-IZO TFT was obtained at a co-sputtering oxygen partial pressure of 2% and GeO2 target power of 10 W.
The fabricated Ge-IZO TFT exhibited an on/off ratio of 3.0×107, a saturation mobility of 13.6 cm2/V·s, a subthreshold swing of 0.98 V/dec, and a threshold voltage of -0.8 V. XPS and XRD analyses of Ge-IZO films were performed to investigate the binding energies of atoms in Ge-IZO films and the crystallinity of the films, and a 90% transmittance of visible light was achieved, which makes the technology useful for transparent devices.