Surface-acoustic-wave resonators

The surface-acoustic-wave (SAW) resonator is the surface-wave equivalent of the crystal resonator now used extensively for stable frequency sources and filters. High-Q operation above 30 MHz, ruggedness, and small size characterize these devices. This paper reviews the current status of SAW resonator developments for the benefit of readers with interest or experience in either crystal resonators or SAW devices. Several typical device geometries are illustrated before providing a qualitative description of resonator operation. Some standard terminology and measurement procedures are proposed, based on similarities to crystal resonators but accounting also for some fundamental differences in loss and coupling mechanisms. Certain irreducible losses which limit the achievable Q of the intrinsic cavity are discussed. Applications are summarized with the aid of two filter examples. A variety of fabrication techniques are being used and none have been fully evaluated, especially with respect to reproducibility, tunability, and stability. Advances in theory, applications, and fabrication are occuring at a rapid rate in this exciting new area.