Material Choice for Optimum SAW Device Performance.

The theory of surface acoustic wave propagation is reviewed and some of the various material design parameters which follow from the theory and which must be considered in making the optimum SAW device substrate choice are discussed. The parameters covered include SAW velocity, piezoelectric coupling constant, electromechanical power flow angle, temperature sensitivity, propagation losses, and beam steering and diffraction. Depending upon the device being designed and the application, some of these parameters are more important than others. In the design of temperature stable, broadband, low insertion loss devices, the important requirements are a zero temperature coefficient of time delay and a large piezoelectric coupling constant. Alternatively, the design of high frequency devices requires low loss substrate materials with large SAW velocities. The state-of-the-art in the development of new materials for these two classes of devices is reviewed. Author