Fabrication of KNbO_3 Thin Film and Application to SAW Device for Future Mobile Tohoku University Communication

在本研究中，采用双阴极溅射法和金属有机化学气相沉积（MOCVD）方法在SrTiO_3 （STO）衬底上沉积KNbO_3薄膜，研究了表面声波（SAW）应用的性能。我们研究了在STO和Si衬底上的KNbO_3薄膜中SAW的理论性质。结果表明，从SAW性能和晶格匹配的角度来看，(001)<100>KNbO_3// (110)<1-10>STO是衬底与KNbO_3薄膜取向之间的最佳组合。在这种情况下，对于1波长的薄膜厚度，机电耦合系数（k^2）为10.4%。我们研究了溅射的最佳靶材组合组成。实验结果表明，K_2CO_3: Nb_2O_5= 1:0和K_2CO_3: Nb_2O_5= 3:1是最佳的选择，在STO基板上成功制备了（001）取向KNbO_3薄膜。利用本课题研究人员研制的扫描非线性介电显微镜（SNDM）观察了KNbO_3薄膜的极化分布。结果表明：在适当的制备条件下，生长的KNbO_3薄膜具有均匀的极化，其方向沿表面法线方向；同时，将极化测量值与实验测量值进行比较，发现两者之间存在较大的相关性。这意味着我们可以在不制作实际声表面波器件的情况下，通过SNDM来估计薄膜的声表面波特性

In this research, properties of KNbO_3 films, which was deposited on SrTiO_3 (STO) substrate using a 2 cathode sputtering method and a metal organic chemical vapor deposition (MOCVD) method, were investigated for surface acoustic wave (SAW) applications.1. We investigated the theoretical properties of SAW in KNbO_3 thin film on STO and Si substrates. As the results, we found that (001)<100>KNbO_3// (110)<1-10>STO was the best combination between the substrate and the orientation of the KNbO_3 thin film in the view of both SAW properties and a lattice matching. In this case, electromechanical coupling coefficient (k^2) is 10.4% for the film thickness of 1 wavelength.2. We investigated a best combination of the targets composition of the sputtering. Experimentally, we found that K_2CO_3 : Nb_2O_5=1 : 0 and K_2CO_3 : Nb_2O_5=3 : 1 was the best one, and we could successfully obtained (001) oriented KNbO_3 thin film on STO substrates.3. We observed the polarization distribution of the KNbO_3 thin films using scanning nonlinear dielectric microscope (SNDM), which was developed by one of the investigators of our research project. The results showed that the as-grown KNbO_3 film had an uniform polarization and its direction was along the surface normal if the film was fabricated by appropriate conditions. Also, as the result of the comparison between the polarization measurements and experimentally measured SAW properties, we could observe a large correlation between them. It means that we can estimate the SAW properties of thin films by SNDM without fabricate an actual SAW device