Deposition of Polycrystalline ZnO Films by Two-Step Method and Characterization of Thermal Annealing Effects
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Deposition of Polycrystalline ZnO Films by Two-Step Method and Characterization of Thermal Annealing Effects Jin-Bock LEE, Myung-Ho LEE, Hye-Jung LEE, and Jin-Seok PARK Department of Electrical Engineering, Hanyang University 1271 Sa 1-dong, Ansan, Kyonggi-do 425-791, South Korea ABSTRACT Polycrystalline ZnO thin films were deposited on SiO2/Si(100) substrate using RF magnetron sputtering. The film deposition performed in this work was composed of following two procedures; the 1st-deposition for 30 min without oxygen at 100 W and the 2nd-deposition with oxygen in the range O2/(Ar+O2) = 10~50 %. Deposited ZnO films revealed a strongly c-axis preferred-orientation (the corresponding texture coefficient ~ 100 %) as well as a high resistivity (> 107 Ωcm). It was also observed that the crystallite size of ZnO was noticeably increased by thermal-annealing. INTRODUCTION With the rapid progress of communication technology, there has been an increasing interest in developing thin-film band-pass filters, including surface acoustic wave (SAW) filters and film bulk acoustic resonators (FBARs) [1,2]. These devices require the thin films to have c-axis preferred orientation, excellent crystallinity, and high electrical resistivity. Polycrystalline ZnO has been considered as one of promising materials for such device applications. The sputtering method has widely been used to obtain the c-axis oriented ZnO film. Very often the impurities (Li, Cu, etc.) and/or the oxygen have been injected during deposition to increase the resistivity of ZnO [2-4]. However, it seems that there is a trade off between the c-axis preferred orientation and the electrical resistivity of ZnO. In the present study a new deposition technique for improving both the c-axis preferred orientation and the resistivity of ZnO film is proposed. In addition, the effect of thermalannealing on the ZnO film is also discussed. EXPERIMENTAL DETAILS ZnO films were deposited on SiO2/Si substrate using RF magnetron sputtering. During deposition the substrate was rotated at a low speed of 5 rpm to enhance the thickness uniformity of deposited films. The deposition method proposed in this work consisted of the 1st-step deposition without addition of oxygen and the 2nd-step deposition with addition of oxygen in the range O2/(Ar+O2) = 10~50 %. In addition, thermal treatment on deposited ZnO films was performed with varying the temperature from RT to 800 oC. Details of deposition and thermalannealing conditions are summarized in Table 1. Texture coefficient (TC) values for c-axis (002)-orientation and crystallite sizes of ZnO films were evaluated from the XRD (X-ray diffractometer, Bede D3 system) spectra. I-V characteristics were measured to calculate the resistivity of ZnO, in the voltage range 0 ~ 1 V H3.13.1 Downloaded from https://www.cambridge.org/core. Columbia University - Law Library, on 10 Aug 2019 at 07:26:45, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-720-H3.13
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