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使用声学λ/4多层的新型压电薄膜谐振器，该谐振器有望在1至20GHz的非常高频率范围内使用，并且可以集成在集成电路中。本研究的主要结果总结如下：1。在考虑传播损耗的情况下，分析了压电薄膜厚度为λ/2的λ/4声学多层压电薄膜谐振器的λ/2模式构型，并计算了电学质量因子Q和有效机电耦合因子K作为多层声阻抗比和层数2的函数。用RHEED和x射线衍射对ecr辅助MBE生长的c轴取向ZnO压电薄膜的质量进行了评价。实验结果表明，可以制备出高质量的ZnO单晶薄膜。提出了一种新的、简单的评价薄膜密度和刚度等声学性能的方法。在该方法中，通过在压电厚模谐振器表面沉积一层测试膜，测量其高泛音谐振频率的变化来评估其声学特性。分析了在压电薄膜中沿表面传播的弹性波的色散特性。结果表明，在有限的电极区会产生被困振动。在Z-cut LiTaO_3衬底上制备了具有5个λ/4声学多层膜的3 ghz压电ZnO薄膜谐振器，该谐振器有望在1 ~ 20GHz的高频范围内使用。

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.