A minimal diffraction cut of quartz for high performance SAW filters

Diffraction has long been a limiting factor in implementing high performance SAW filters on ST-quartz. A minimal diffraction Quartz cut would find significant interest in the SAW industry. By proper selection of the Euler angles, the effects of diffraction may be minimized while simultaneously maintaining near zero power flow angle (PFA) and temperature coefficient of frequency (TCF). Using this approach, a new orientation of quartz has been identified. The resulting optimal region of Euler angles is (-5° to +5°, 37° to 46°, 20° to 26°). Doubly rotated wafers can introduce additional significant variations in the manufacture of SAW devices. Therefore a more restricted, but potentially more useful, range of Euler angles is (0°, 40° to 46°, 20° to 26°). A nominal solution is (0°, 43°, 23.7°) Over this range the coupling coefficient is approximately 15% greater than that of ST-quartz. Therefore, while maintaining near zero PFA and room temperature TCF, and slightly improved coupling, the effects of diffraction have been dramatically reduced. The theoretical background and experimental results of this development are presented. Additionally, a comparison of a SAW filter fabricated on ST-quartz and the new minimal diffraction orientation is presented