Interferometric Measurements of Dispersion Curves and Transmission Characteristics of the Acoustic Mirror in Thin Film BAW Resonator

A heterodyne laser interferometer is used for a detailed study of acoustic wave fields excited in a 932 MHz ZnO solidly mounted BAW resonator. The sample is manufactured onto a glass substrate, which allows for direct measurement of the vibration fields from the bottom of the mirror stack. The vibration fields are measured both on top of the resonator and at the bottom of the mirror stack. Dispersion curves are calculated from the experimental data in both cases. This enables comparison between the vibration amplitudes on top of the resonator with those at the bottom of the mirror stack, and hence allows to determine the transmission characteristics of the acoustic mirror within the measured wave-vector, frequency space. The experimental dispersion curves and mirror transmission are compared with simulations.