Theoretical and Experimental Identification of Love Wave Frequency Peaks in Layered Structure ZnO/Quartz SAW Device

In this paper, the layered structure ZnO/Quartz (90 $^{\circ}$ rotated ST-cut) is investigated theoretically and experimentally. Both waves, Rayleigh and Love, are analyzed. Dispersion curves of phase velocities, electromechanical coupling coefficient $(K ^{2})$ and temperature coefficient of frequency (TCF) were calculated as a function of normalized thickness ZnO film $(kh_{\rm ZnO} = 2\pi h _{\rm ZnO} /\lambda)$ and the optimum value of $h _{\rm ZnO}$ was determined for experimental study. Experimental results combined with simulation lead to clearly identify the generated waves and their higher modes in this structure except the mode 0 that shows comparable velocity for both Rayleigh and Love waves. The identification of the wave type was performed by studying the frequency response of the device with or without a droplet of water in the wave path. We also demonstrate that the highest elastic velocity is obtained for the mode 1 of the Love wave. This Love wave mode exhibits very interesting electrical characteristics, good $K ^{2}$, high-frequency rejection, low TCF, and very low attenuation in liquid making it very attractive for gas and liquid sensor applications.