New Piezoelectric Thin Film Resonator Promising for Use in Very High Frequency Communication Systems

本研究的目的是研究一种新的压电薄膜谐振器，使用声学λ/4多层膜，这是有前途的，在很高的频率范围从1到20 GHz的使用，并可以集成在集成电路中。本研究的主要结果总结如下。考虑传播损耗，分析了压电薄膜厚度为λ/2的λ/4声多层膜谐振器的λ/2模态结构，计算了压电薄膜谐振器的电学品质因数Q和有效机电耦合系数K随声阻抗比和层数的变化.利用RHEED和X射线衍射对ECR辅助分子束外延生长的c轴取向ZnO压电薄膜的质量进行了评价。证实了可以生长出高质量的ZnO单晶薄膜.提出了一种新的薄膜声学性能（密度和刚度）的简单评价方法。在该方法中，声学特性从由于在谐振器表面上沉积测试膜而测量的压电厚度模式谐振器的高泛音的谐振频率变化来评估。分析了弹性波在压电薄膜中沿着表面传播时的频散特性。结果表明，在有限电极区域内可以产生振动.在Z切LiTaO_3基片上制备了一种3 GHz的具有5个λ/4声学多层膜的ZnO压电薄膜谐振器，这种谐振器在1 ~ 20 GHz的甚高频范围内有应用前景。

The purpose of this study is to investigate a new piezoelectric thin film resonator using acoustic λ/4 multilayers, which is promising for use in a very high frequency range from 1 to 20GHz and can be incorporated within integrated circuits. The main results of this study are summarized below.1. The λ/2 mode configuration of piezoelectric thin film resonator using acoustic λ/4 multilayers, where the piezoelectric film is λ/2 thick, was analyzed in consideration of propagation loss, and then electrical quality factor Q and effective electromechanical coupling factor K were calculated as functions of the acoustic impedance ratio of multilayers and the layer number.2. The quality of c-axis oriented piezoelectric ZnO films grown by ECR-assisted MBE were evaluated with RHEED and X-ray diffraction. It has been confirmed that high quality ZnO single crystal films can be grown.3. A new simple evaluation method for acoustic properties, such as density and stiffness, of thin films was proposed. In this method, the acoustic properties are evaluated from the measured resonance frequency change of high overtones of a piezoelectric thickness-mode resonator due to deposition of a test film on the resonator surface.4. Dispersion characteristics of elastic waves which propagate along the surface being trapped in a piezoelectric film were analyzed. It has been shown that a vibration trapped in the finite electroded region can be occurred.5. A 3-GHz piezoelectric ZnO film resonator with five λ/4 acoustic multilayers was fabricated on a Z-cut LiTaO_3 substrate and this type of resonators were shown to be promising for use in a very high frequency range from 1 to 20GHz.