SH-type Spurious Response Free TC-SAW Resonators Using Low Acoustic Velocity Rayleigh SAW on LiNbO3 Substrate

In this paper, we describe the behavior of the spurious response caused by shear-horizontal (SH) type surface acoustic wave (SAW) in low acoustic velocity (LAV) Rayleigh SAW structure, which realizes remarkable miniaturization of high performance temperature compensated SAW (TC-SAW) devices. It is well known that an SH or Rayleigh type spurious response appears near the main response on TC-SAW on LiNbO3 (LN) substrates and causes various undesired effects on the device characteristics. These effects can be removed by two means; one is minimization of its electromechanical coupling factor (K-2), and the other is expulsion of it from the filter passband. However, they are often non-negligible in practical use. In order to explore a solution of this problem, we both theoretically and experimentally investigated the variation of the K-2 and the frequency of the SH-type SAW in the LAV-Rayleigh SAW structure. As a result, we revealed that the K-2 can be kept almost zero even if various parameters are changed. Moreover, if higher density metal like Pt is used as a main electrode material, large frequency difference between the main and spurious responses is achievable to exclude the spurious response from filter passbands. Therefore, very small sized and SH-type spurious response free TC-SAW devices can be realized using the LAV-Rayleigh SAW technology.