Acoustic loss mechanisms in leaky SAW resonators on lithium tantalate

We discuss acoustic losses in synchronous leaky surface-acoustic wave resonators on rotated Y-cut lithium tantalate substrates. Laser probe measurements and theoretical methods are employed to estimate the radiation of leaky waves into the busbars of the resonator and the excitation of bulk-acoustic waves. We find that the escaping waves lead to a significant increase in the conductance, typically in the vicinity of the resonance and in the stopband, but that they do not explain the experimentally observed deterioration of the electric response at the antiresonance. At frequencies above the stopband the generation of fast shear bulk-acoustic waves is the dominant loss mechanism