John G. Gualtieri
John A. Kosinski
U.S. Army Res. Lab., AMSRL-EP, Fort Monmouth, NJ 07703-5601
Piezoelectric crystal resonators for frequency control and selection are characterized primarily by the values of their acoustic quality factor, Q. Depending on the application, other measures, such as the electromechanical coupling factor are also used. None of the usual performance figures is entirely adequate for characterizing resonators for applications at high frequencies. This paper describes various metrics traditionally applied to resonators, such as acoustic Q, coupling factor, and equivalent circuit parameters. It tabulates observed values for older materials like quartz and lithium niobate and newer substances such as langasite and thin-film aluminum nitride. It then introduces a new metric for judging material suitability for high-frequency resonator use, and tabulates these values. The new measure combines all physical quantities associated with acoustic wave propagation in piezocrystals: mass density, dielectric permittivity, piezoelectric modulus, elastic stiffness, and viscosity. Its use leads to a number of unobvious constraints on the future technology.