Ferroelectric materials for thin-film and membrane resonators

Ferroelectrics are attractive as thin-film driver layers for high frequency resonators because of their piezoelectric nature. We consider various measures of performance usually applied to resonator materials, and list observed values for various ferroelectrics being developed for use in cellular radio and collision-avoidance radar. For these applications, our analysis shows that the material parameter of paramount importance is neither the electromechanical coupling nor the acoustic quality factor. We introduce a new metric for judging material suitability for high frequency resonator use. It is a combination of all of the physical quantities associated with acoustic wave propagation in piezoelectrics. Ranking ferroelectric thin-film materials by use of the new measure leads to a number of unconventional implications regarding the future technology of these devices.