Microwave Surface Acoustic Wave Materials

Abstract

Abstract : The acoustic wave properties of several piezoelectric crystals and a layered structure have been theoretically and experimentally investigated for possible application in microwave acoustic devices. A search was made for crystals and layered structures having one or more of the following properties: (i) temperature compensation, (ii) high piezoelectric coupling, (iii) low power flow angle, (iv) low loss and (v) low or high acoustic wave velocities. The acoustic waves studied were the bulk acoustic waves (BAW), the surface acoustic waves (SAW), the pseudo SAW (PSAW), the plate modes and the surface skimming bulk waves (SSBW). The wave properties studied were the velocity, piezoelectric coupling, the temperature coefficient of delay, diffraction and attenuation. The layered geometries examined studied included fused silica on LiNbO3 and gold, aluminum and copper layers on quartz. The overlay structures were found to be more temperature stable than the single crystals. A theory describing the spectrum of acoustic waves emanating from an interdigital transducer was developed. Several promising cuts for SSBW in quartz were identified and studied both theoretically and experimentally. Finally, various prototype SSBW devices were fabricated and tested.