SUPPRESSION OF THE LEAKY SAW ATTENUATION WITH HEAVY MECHANICAL LOADING

We discuss effects on the propagation of surface acoustic waves (SAW) due to heavy mass loading on Y-cut lithium niobate and lithium tantala te substrates, An abrupt reduction in the leaky-SAW (LSAW) attenuation is observed in the measured admittance of a long resonator test struc ture on 64 degrees-YX-cut lithium niobate for aluminum electrodes of t hickness h/lambda(0) beyond 9-10%. This experimental fact is explained theoretically as the slowing down of the leaky wave below the velocit y of the slow shear surface-skimming bulk wave (SSBW), such that energ y dissipation into bulk-wave emission becomes inhibited. An infinite t ransducer structure is modeled using the periodic Green's function and the boundary-element method (BEM); the computed theoretical propertie s well explain for the experimental findings. The model is further emp loyed to quantify the leaky surface-wave attenuation characteristics a s functions of the crystal-cut angle and the thickness of the electrod es. The resonance and antiresonance frequencies and the corresponding Q values are investigated to facilitate the selection of crystal cuts and electrode thicknesses. The transformation of the leaky SAW into a SAW-type non-leaky wave is also predicted to occur for gold electrodes , with considerably thinner finger structures.