Analysis of Piezoelectric Thin Film Resonators with Acoustic Quarter-Wave Multilayers

Two configurations of piezoelectric film resonators with acoustic quarter-wave multilayers, which are promising for use in a very high frequency range from 500 MHz to over 10 GHz, are theoretically analyzed using equivalent circuits and the characteristics of the two configurations are discussed with emphasis on their differences. It has been shown that the number of multilayers required for saturation of Q decreases with an increase in the impedance ratio of multilayers and that the effective electromechanical coupling factor has a certain value independent of the layer number. In the λ/4 mode configuration, however, the bottom electrode is located at the strain maximum and therefore the resonator charateristics are influenced by the electrode material. The λ/2 mode configuration appears to be slightly more favorable than the λ/4 mode configuration.