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Propagation characteristics of surface acoustic waves under hexagonal phononic gratings

Dispersion characteristics of surface acoustic waves (SAWs) propagating along the c-plane of single crystalline AlN under 2D tungsten (W) hexagonal gratings are studied using eigen-frequency and frequency response finite element analysis. Specifically, a 2D hexagonal grating with a 10μm distance between the W masses is considered and the frequency stopband SAW characteristics studied. For hexagonal W gratings with a thickness above a critical value (about 0.9μm in this case) SAW stopbands with a 0 rad and π/6 rad angle of incidence penetrate in each other thus forming a forbidden SAW frequency band lying between the upper stopband edge of the 0 rad incident SAW and the lower stopband edge of the π/6 rad incident SAW. In view of the above findings the existence of a complete frequency stopband is discussed.