| AVS 56th International Symposium & Exhibition | |
| Thin Film | Friday Sessions |
| Session TF-FrM |
| Session: | Transparent Electronic Materials and Applications |
| Presenter: | Y. Nishi, Aoyama Gakuin University, Japan |
| Authors: | Y. Nishi, Aoyama Gakuin University, Japan K. Hirohata, Aoyama Gakuin University, Japan N. Tsukamoto, Aoyama Gakuin University, Japan Y. Sato, Aoyama Gakuin University, Japan N. Oka, Aoyama Gakuin University, Japan Y. Shigesato, Aoyama Gakuin University, Japan |
| Correspondent: | Click to Email |
Transparent conductive oxide (TCO) is a highly degenerated wide band-gap semiconductor with low electrical resistivity and high transparency in the visible and near-infrared regions. Al-doped ZnO (AZO) should be promising potential alternative to In-based TCO, such as ITO or IZO. AZO films have been prepared by magnetron sputtering using ceramic targets because of the various advantages for uniform depositions in large area. In general the deposition rate for the sputtering using the oxide ceramic targets is not so high and also the cost for the high quality ceramic targets is high. On the other hand, reactive sputtering using Zn-Al alloy targets is considered to be one of the most promising techniques to achieve much higher deposition rate for various industrial applications because sputtering yield of the metallic surface is much larger than oxide surface and also the higher sputtering power density can be applied for metallic targets because of their higher thermal conductivity. The reactive sputtering process, however, is strongly affected by the O2 flow ratio; the deposition rate exhibits hysteresis with respect to the O2 reactive gas flow rate. Such behavior originates in the oxidation state of the target surface, resulting in the marked decrease in deposition rate with the increasing O2 flow. Therefore, the sputtering conditions should be precisely controlled so as to obtain high-quality AZO films by reactive sputtering with a high deposition rate and with high reproducibility. In this study, AZO films were deposited on quartz glass substrates, unheated and heated at 200oC, using reactive sputtering with a specially designed feedback system (Fraunhofer Institut fur Elektronenstrahl-und Plasmatechnik, FEP) of discharge impedance combined with mid-frequency (mf) pulsing [1] . A planar Zn-Al alloy target (Al: 1.5wt.%) was connected to the switching unit, which was operated in a 50 kHz unipolar pulse mode [2] . Oxidation of the target surface was precisely controlled by the feedback system control the entire O2 flow ratio in the “transition region”. The deposition rate was about 10-20 times higher than the one deposited by conventional sputtering depositions using oxide ceramic targets. For the AZO films deposited on the glass substrates heated at 200oC with a discharge power of 4000 W, the deposition rate was 390 nm/min, where the resistivity of the films was 3.8×10-4 Ωcm and transmittance in the visible region was 85 %.
[1] M. Kon, P.K. Song, Y. Shigesato, P. Frach, A. Mizukami and K. Suzuki, Jpn. J. Appl. Phys. 41, 814 (2002).
[2] S. Ohno, N. Takasawa, Y. Sato, M. Yoshikawa, K. Suzuki, P. Frach and Y. Shigesato, Thin Solid Films 496, 126 (2006).