The experimental SAW propagation characteristics of LiNbO3 and LiTaO3 with free and metallized surfaces

The SAW propagation properties of 41 degrees and 64 degrees Y-X LiNbO3, and 36 degrees Y-X LiTaO3 have been characterized experimentally with and without a shorting surface in the propagation path. The experiments were carried out over a frequency region from 40 MHz to above 1.0 GHz with pairs of interdigital transducer electrodes with a 100 nm film of aluminum present or absent between adjacent IDTs. The presence of the different modes and their characteristic velocities are in good agreement with theoretically predicted values. The propagation loss for the PSAW and HVPSAW modes behaved in a different fashion depending upon the presence or absence of the shorting surface. As predicted, the PSAW mode loss is lower for the free surface of the 41 degrees LiNbO3 and lower for the metallized surface on the 64 degrees LiNbO3. The propagation loss for the 36 degrees LiTaO3 was higher for the metallized surface which is not anticipated from theoretical considerations. The PSAW loss for the 36 degrees LiTaO3 displayed a strong reduction in dB/cm. propagation loss above 1.0 GHz for the metallized surface.