Research for the deposition of new piezoelectric Ta_2O_5 films and their application to the communication device.

Ta_2O_5薄膜已被用于形成薄膜电容器，最近还用于光学波导和太阳能电池的抗反射涂层。这些应用基本上是基于这种氧化物的高化学稳定性，特别是其最佳的光学性能，如高折射率和非常低的光吸收系数。在以前的工作中，Ta_2O_5薄膜是通过热氧化蒸发到衬底上的钽膜，射频溅射和反应直流溅射得到的。在以前的工作中获得的Ta_2O_5薄膜都是无定形的，而不是单晶。在本研究中，我们明确了以下三点。(1)首次测定了Ta_2O_5薄膜的材料常数。采用直流二极管溅射法制备了x轴取向Ta_2O_5薄膜。材料常数由在层状基底上传播的体波和表面声波的相速度和机电耦合常数确定。(2)将Ta_2O_5薄膜应用于表面声波卷积器。与yz、LiNbO3单晶的转换效率进行了比较。结果表明，Ta_2O_5薄膜具有应用于非线性声学器件的可能性。此外，还报道了Ta_2O_5单晶为铁弹性材料。^<10>这种单晶可以应用于电气和光开关器件。

Ta_2O_5 thin films have been used for forming thin-film capacitors and, more recently, for optical wave-guides and for antireflection coating on solar cells. These application are essentially based on the high chemical stability of this oxide and especially on its optimum optical properties such as a high refractive index and a very low absorption coefficient for light.In previous works, the Ta_2O_5 thin films were obtained by he thermal oxidation of a tantalum film evaporated onto a substrate, rf sputtering, and reactive dc sputtering. All Ta_2O_5 thin films obtained in previous work were amorphous, and were not single crystals.In this research, We have clarified next three points.(1) The first measurement of the material constants of Ta_2O_5 thin films was investigated. X-axis oriented Ta_2O_5 thin films were deposited on the fused quartz by using the dc diode sputtering method. The material constants were determined from the phase velocity and the electromechanical coupling constant of the bulk waves and the surface acoustic waves propagating on the layered substrate.(2) The Ta_2O_5 thin film was applied to the surface acoustic wave convolver. The conversion efficiency of the convolver compared, favorably with one of Y.Z,LiNbO3 single crystal. This result shows that the Ta_2O_5 thin film has a possibility to the applicable to the nonlinear acoustic device.In addition, it was reported that single crystal of Ta_2O_5 was ferro-elastic material.^<10> This single crystal may be able to be applied to electrical and optical switching devices.