Fundamental properties of thin film resonators

The author presents an overview of the physical properties of thin film resonators, composite resonators using piezoelectric thin films, and filters employing coupled resonators. There are both similarities and substantial differences between thin-film resonators and conventional single-crystal resonators used at low frequencies. For most applications the thin-film resonator is fabricated with lateral dimensions in excess of 50 to 100 times the thickness and as such can be considered a one-dimensional device for the purposes of wave propagation and circuit modeling. Composite resonators consisting of piezoelectric films supported by membranes or bulk substrates form an important part of the thin-film resonator technology. An analysis of the general quasi-mode composite resonator is presented, and the results are summarized in electrical impedance equations cast in a matrix algebra format