A simple phenomenological model of tunable SAW devices using magnetostrictive thin films

A simple phenomenological model has been developed that is useful for the approximate design of tunable SAW (surface acoustic wave) devices using magnetostrictive thin films. The model formulation, based on perturbation theory, relates the maximum magnetic-field-dependent velocity change or tunability range to the frequency of operation, film thickness, elastic properties of the film and substrate, and magnetic properties of the film. Iron-terbium-boron films deposited on quartz and lithium niobate substrates were used to verify the formula. A significant variability in the magnetic properties of the films was obtained by varying the amount of terbium (0-5 at.%) in the film (80% Fe and 15-20% B). A simple figure of merit for comparing various film-substrate combinations, independent of device dimensions, was derived and experimentally checked.