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In this paper, we present the resonance frequency spectra features of a composite resonator consisting of a piezoelectric film and a substrate plate. Based on those features, a direct method to characterize the piezoelectric film with two electrodes is presented. By directly using the parallel and series resonant frequency spectra of the HBAR, the electromechanical coupling factor, the density and the elastic constant of the piezoelectric film can be obtained directly. Some problems related to the accuracy of the method, especially the effect of the electrodes, are discussed.

Simulation results for three kinds of HBARs with different piezo-film and substrate combinations are presented. Based on the distributions of the resonance frequency spacing , with the thickness of the substrate are calculated. Those data give some guidelines to choose the thickness of the substrate for compromising the parameters of the operating mode. Results showed that it is unnecessary to choose very thick substrate for obtaining high Q. Actually, high Q can be obtained when the thickness ratio to the film reaches about 50 to 150 for the three different kinds of samples.