Suppression of transverse waveguide modes for SAW resonators with Pt and Pt/Rh/ZrO2 electrodes

In this work, spurious transverse waveguide modes were suppressed from the frequency responses of Pt-electrode resonators on ST-X quartz [0°, 132.75°, 0°] and Pt- and Pt/Rh/ZrO₂-electrode resonators on LGS [0°, 144°, 24°] through the design of the gratings, aperture, and transducers' active area. In particular, it will be shown that conventional shorted gratings cannot be used with Pt or Pt/Rh/ZrO₂ electrodes, since the velocity discontinuity between the grating and the bus bar leaks energy from the active area. Scalar potential theory is utilized to adjust the ratio of a transducer's active area to the total aperture, such that higher-order transverse waveguide resonances are filtered from the frequency response.