Parasitic BAW excitation in LSAW transducers

The parasitic excitation of bulk acoustic waves at high frequencies in synchronous leaky surface-acoustic wave resonators is studied experimentally in 36° and 42° YX-cut lithium tantalate. To characterize the strength of the bulk-wave excitation, the admittance curves measured from test structures with varying apertures, metallization ratios, and the number and the thickness of the aluminum electrodes are fitted numerically to a modified coupling-of-modes model. A theoretical formula for the dependence of the level of the bulk-wave excitation on the coupling-of-modes parameters is proposed