ST34°切割石英上表面横波的金属栅阵反射特性

The Reflection Characteristics of Surface Transverse Wave under Metal Strips on ST34° Cut Quartz

由于表面横波(STW)器件具有温度稳定性好、声速高、功率处理能力强等优点,过去几年中,人们愈来愈重视发展STW器件.金属反射栅是谐振器及谐振型滤波器的重要组成部分,其性能的好坏对整个器件的性能影响很大,此前对金属反射栅特性的一些理论计算是在假设每根指条的金属化比和金属膜厚都完全一样的条件下获得的模拟结果,而且模式转化也很难精确估计,这就带来了理论计算与实验结果的明显差异.研究的主要目的是在实验上揭示表面横波在金属反射栅阵下传播的基本特性,为石英上STW高频谐振型器件的设计与开发提供实验数据.文中对ST34°切石英上SAW与STW的金属栅阵反射特性进行了实验比较.试验结果表明,在相同条件下STW的金属栅阵反射效率要高于声表面波(SAW)的反射效率,它与SAW金属反射栅阵的本质区别是不论短路还是开路栅阵,STW的金属栅阵反射中心都低于换能器的激发中心.为验证实验结果,文中设计了915MHz的STW单端对谐振器,其中换能器与反射栅的频率差取值比声表面波小,而且反射栅也由301根减到201根,测试结果表明谐振器的插入损耗和Q值等关键参数没有明显退化.

Because of the advantages including temperature stability, high velocity and enhanced power-handling capability, surface transverse wave （STW） devices have been become increasingly important over the last few years. As the most fundamental element of STW devices, the performance of STW devices is mainly depend on the metal reflector, but the previous theory simulations for metal reflector are based on the fixed metallization parameters, the variation of the metal film thickness and finger-to-gap ratio is ignored, while not only the velocity but also the electromeehanical coupling coefficient is a function of the metallization parameters, moreover the mode conversion is difficult to predict accurately, so the agreement between theory and experiment is not very good. The primary purpose of this investigation is to discover the basic behavior of the STW under metal strips in experiments, and to guide the design and development of high frequency STW resonators and resonator filters on quartz. In this paper, the reflection characteristics of metal strips of surface acoustic waves （SAW） and STW on ST34° quartz are compared by experimental study. The results indicate that, in the same condition, the reflection coefficient of STW is higher than that of SAW, and for both short-circuited strips as well as open-circuited strips, the reflection center frequency is slightly lower than that of inter-digital transducer （IDT）with split fingers, which is the main difference to SAW＇s. As example, this paper designed a one-port STW resonator with center frequency 915 MHz, which the frequency discrepancy between IDT and reflectors is smaller than SAW＇ s and the short-circuited metal strips are reduced from 301 to 201, the experimental results show that the key parameters including insertion loss and Q value are not degraded.