Surface Acoustic Wave Resonators on Quartz

Abstract

Abstruct-The design of highQ lowdistortion surface acoustic wave (SAW) resonators requires techniques and data for minimizing acoustic losses and accurate placementof the device resonance. Several aspects of one- and two-port SAW resonator design and fabrication are discussed. It is shown that devices on quartz consisting of recessed aluminum transducers and shallow reflecting groove arrays can be fabricated with very high Q values. The properties of the shallowgrooved reflector are analyzed both experimentally and theoretically. Experimental valuesof the surface wave velocities for reflectors, transducers, and the free surface are reported, and transducer placement and maximum cavity length are discussed. It is shown that the maximum cavity length possible, without additional resonant modes, increases asthe goove depth decreases. Cavity length corrections required to center a resonance in the reflector stopband are derived, and resonator fabrication for the recessed-transducer/shallowgrooved reflector configuration is discussed. SAW devices with Q values of 75 000 (at 71 MHz) and resonators at frequencies above one GHz (with Q values over 3200) have been fabricated.