Effect of Substrate Thickness on Quasi-Longitudinal Leaky Surface Acoustic Wave Propagation on Quartz

概要

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Propagation properties of a quasi-longitudinal leaky surface acoustic wave (QLL-SAW) on rotated-Y cut quartz are described. It is found that by reducing the relative thickness of the quartz substrate, i.e., the ratio of the substrate thickness to the SAW wavelength, the $Q$-value of a QLL-SAW resonator can be improved. Its phase velocity is about 5704 m/s, which is close to the velocity of a longitudinal BAW (5750 m/s) and about 1.8 times that of a Rayleigh SAW. Propagation characteristics are simulated by a finite element method. The results obtained indicate that many guided wave modes exist near the velocity of the longitudinal BAW and strongly couple to QLL-SAW modes. Experimental results show that these guided wave modes affect QLL-SAW propagation and deteriorate resonator $Q$-values. By reducing the relative thickness of the quartz substrate, the frequency difference between the QLL-SAW and the guided wave modes is increased, which weakens the coupling. As a result, 700 MHz SAW resonators having a $Q$-value of more than 8000 are realized.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-05-30