| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Ji-in Park, Pusan National University, Republic of Korea |
| Authors: | J.I. Park, Pusan National University, Republic of Korea Y.S. Lim, Pusan National University, Republic of Korea M.H. Jang, Pusan National University, Republic of Korea S.I. Choi, Pusan National University, Republic of Korea N.G. Hwang, Pusan National University, Republic of Korea M.S. Yi, Pusan National University, Republic of Korea |
| Correspondent: | Click to Email |
We investigated the effect of aluminum oxide (Al2O3) passivation layer on the stability of aluminum-indium-zinc oxide (Al-IZO) thin-film transistors (TFTs) under positive bias stress (PBS) and negative bias illumination stress (NBIS). 20-nm thick Al-IZO channel layers were deposited by radio-frequency (RF) magnetron co-sputtering, and then annealed in air for 1h at 250℃. Processing parameters such as the IZO, Al2O3 target power (50, 10W) and oxygen partial pressure (13%) were fixed. After depositing the channel layers, 20-nm thick Al2O3 passivation layers were deposited by RF magnetron sputtering at room temperature, and annealed again at 250℃.
The TFTs without any passivation were taken as reference devices for comparison (device A). Fig. 1 shows the cross-sectional schematic diagram of Al2O3 passivated Al-IZO TFTs (device B). The measured electrical parameters of each device were summarized in Table 1, and it indicates that Al-IZO channel layer is not degraded during the passivation layer deposition by sputtering.
Fig. 2 (a) and (b) show the transfer characteristic curves the device A and B depending on the stress durations (7200 s) under the positive bias stress (VGS= +20V, VDS= 0V, PBS) in dark, respectively. It can be easily seen that threshold voltage shift (ΔVth) of the device B is much smaller than that of the device A, and indicates that more charge trapping sites (O2+e-→O2-) is created in device A during PBS condition. In other words, Al2O3 passivation layer could effectively prevent the oxygen absorption on surface of the Al-IZO film under the influence of gate voltage stress.
To investigate the stability of the TFTs under bias illumination stress, a negative bias stress (VGS= -20V, VDS= 0V, NBS) were repeatedly applied to the device A and B under green light illumination in air for 7200s. The brightness of the green light source was 2047cd/m2. Fig. 3 (a) and (b) show the evolution of the transfer characteristic curves of each device for various stress durations under NBIS condition, and it can be concluded that the stability of device B is better than that of device A under NBIS condition. In general, the degradation mechanism of the NBS under illumination of Al-IZO TFTs is dominated by the photo-generated hole trapping states (Vo→Vo2++2e-) at gate insulator and/or interface between insulator and channel. In this result, the Al2O3 passivation layer could effectively passivate the defect in the Al-IZO films. We demonstrated that the Al2O3 could be an effective passivation layer to suppress O2 absorption on Al-IZO back channel and decrease photo-excitation on Al-IZO films.