Abstract

Resonant Spectrum Method , a direct method to characterize a piezoelectric film which is deposited on a substrate to form a composite resonator (also known as over-moded resonator), has been developed. Based on the parallel and series resonant frequency spectra of a composite resonator, with the calculation of the spacing of the parallel resonant frequencies and the effective coupling coefficient, the electromechanical coupling factor, the density, and the elastic constant of the piezoelectric film can be evaluated directly. Experimental results on samples consisted of ZnO films on fused quartz substrates with different thicknesses are presented. They show good agreement with numerical simulations. The effects of the electrode thickness, the mechanical loss and the contact/electrode resistance on the accuracy of this method have also been investigated and it is found that the electrode thickness manifestly affects the accuracy of the method. The mechanical loss of the piezoelectric film has no significant impact. The contact/electrode resistance has some effect but this can be corrected. Applications of the method in piezoelectric film characterization and resonator filter design have been described.