Research for the deposition of new piezoelectric <Ta_2O_5> single crystal films and their physical properties.

<Ta_2O_5>薄膜已经用于形成薄膜电容器，并且最近用于光波导和用于太阳能电池上的电介质涂层。这些应用基本上基于这种氧化物的高化学稳定性，特别是基于其最佳光学性能，例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>薄膜是通过热氧化的钽膜蒸发到基板上，射频溅射，和反应直流溅射。本<Ta_2O_5>研究中，我们澄清了以下三点：（1）<Ta_2O_5>薄膜是用平面磁控反应直流二极管溅射法制备的。通过改变溅射条件，可以制备出取向、非晶和多晶薄膜。特别地，取向膜是单轴取向膜，其中<beta><Ta_2O_5>属于点群“m“的X轴垂直于基板生长。此外，该薄膜还具有压电性能，是一种新的压电薄膜，目前还未见报道。(2)在取向薄膜中<Ta_2O_5>，对于表面声波的最大机电耦合系数&lt;K^2&gt;在hk=1.6时为1.54%。当使用熔融石英衬底时，SAW的传播损耗在131 MHz处为13.3 dB/cm。(3)取向薄膜的一阶TCD<Ta_2O_5>为零。在hk=1.27时，PYREX基片的二阶TCD为0.052ppm/&lt;C^2&gt;，而在hk= 1.78时，熔融石英基片的TCD为0.148ppm/&lt;C^2&gt;<Ta_2O_5>.期望制备出<Ta_2O_5>性能更加优异的薄膜。

<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 the 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 that(1) the <Ta_2O_5> thin films are fabricated by the planar-magnetron reactive DC diode sputtering method. These kind of films such as oriented, amorphous and polycrystalline can be fabricated by varying the sputtering condition. Especially, the oriented film is one axis oriented film where the x-axis of <beta> - <Ta_2O_5> belonging to point group " m " is grown perpendicular to the substrate. Furthermore the film shows piezoelectric properties and is a new piezoelectric film which has not been reported thus far.(2) In the oriented <Ta_2O_5> thin film, the maximum electromechanical coupling coefficient <K^2> for the surface acoustic wave is 1.54% at hk=1.6. The propagation loss of the SAW is 13.3 dB/cm at 131 MHz when the fused quartz substrate is used.(3) The first-order TCD of the oriented <Ta_2O_5> thin film is zero. The second-order TCD is 0.148 ppm/ <C^2> at hk=1.78 for the fused quartz substrate and is 0.052ppm/ <C^2> at hk=1.27 for the PYREX substrate, respectively.The <Ta_2O_5> film is chemically stable and may supply SAW device with good temperature characteristics. The fabrication of <Ta_2O_5> thin film with more excellent properties is expected.