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

Ta_2O_5薄膜被用来形成薄膜电容器，最近又被用来制作光波导和太阳能电池的减反射涂层。这些应用基本上是基于这种氧化物的高化学稳定性，特别是它的最佳光学性质，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薄膜是通过蒸发到衬底上的Ta_2O_5薄膜热氧化、射频溅射和反应直流溅射获得的。前人工作中得到的Ta_2O_5薄膜都是非晶态的，不是单晶的。在本研究中，我们澄清了以下三点：(1)首次测量了Ta_2O_5薄膜的材料常数。采用直流二极管溅射法在熔融石英衬底上制备了X轴取向的Ta_2O_5薄膜。由体波和声表面波在层状衬底上传播的相速度和机电耦合常数确定了材料常数。(2)将Ta2O5薄膜应用于声表面波卷积器。卷积器的转换效率与Y.Z，LiNbO_3单晶的转换效率相当。这说明Ta_2O_5薄膜有可能应用于非线性声学器件。此外，有报道称Ta_2O_5单晶是铁弹性材料。该单晶有望应用于电光开关器件。

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.