Epitaxial growth of LiNb0 3 thin films by excimer laser ablation method and their surface acoustic wave properties
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Epitaxial growth of LiNbO3 thin films by excimer ablation method and their surface acoustic wave properties. Yoshihiko Shibata*, Kiyoshi Kaya*, Kageyasu Akashi*, Masaki Kanai**. Kawal** and Shichlo Kawal** *Kawasaki Laboratory, Corporate research Laboratories (Tokyo), Chemical Industry Co., Ltd. Yakoh, Kawasaki,Kanagawa 210 Japan **The Institute of Scientific and Industrial Research, University, Mihogaoka, Ibaraki, Osaka 567, Japan
laser
Tomoji Asahi Osaka
ABSTRACT We have formed epitaxial LINbO thin films on sapphire substrates (001),(110) and (012) using an excmer-laser ablation technique. We have fabricated surface acoustic wave (SAW) filters on the films and evaluated SAW properties. It is demonstrated that the LiNbO thin films on the sapphire substrates are candidates for a high frequency SAW filter because of their high velocities of propagation (5300-5600m/s). INTRODUCTION Lithium niobate (LINbO 3) Is one of the most fascinating materials because of its excellent piezoelectric and electro-optic coefficients. Recently, thin films of LiNbO3 have been formed by RF-magnetron sputtering, molecular beam epitaxy, and sol-gel methods and there have been a few reports by laser ablation methods. We have applied a laser ablation method to preparation of LINbO3 films and succeeded in forming epitaxial LiNbO3 films on sapphire substrates (001), (110) and (012). We have observed interesting epitaxial relationships between LiNbO3 films and the sapphire substrate. The as-grown LINbO3 films have enough piezoelectricity to fabricate SAW filters. In this paper, we report the preparation of the epitaxial LINbO thin films on sapphire substrates using an excimer-laser ablation technique and the SAW properties of these films. EXPERIHENTAL We have used t3 e same experimental setup for the laser ablation as described earlier. The targets were 10-15 mm$ disks of LI-Nb-O ceramics prepared by sintering a mixture of Li 2 CO3 and Nb20 5 powders in air at l1OOC for 3h. The Li/Nb ratios of the targets were in tne range of 1.0-3.0. The composition of the targets were confirmed by Inductively coupled plasma (ICP) method. The ArF excimer-laser (Lambda Physik, LPX 210 193nm) beam was focused on the target with the frequency of 15 l1z. The thin film was deposited on the substrate located at the opposite side of the target In the presence of 02 and 03 gas. TIve content of 03 was 8% and the total gas pressure was in the range of 5x10 - lx10 torr. The substrates used were (001), (110) and (012) planes of Al0 3 single crystals (sapphire c,a and r-planes),(Kyocera, Union Carbide), ani were heated at 500-800 0 C during the deposition. The distance from the target to the substrate was 3 cm. The angle between the incident laser beam and the perpendicular direction of the target surface was 60 . The growth rate of the films was 0.2-0.6 pm/h and the total thickness was 0.1-0.7 pm. The crystal structure and crystallographic orientation of the films were determined with x-ray diffraction (Rigaku, RAD-C), x-ray pole figures (Rigaku, RAD-B, B-8) by Schulz
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