Selective mode excitation of piezoelectric disk-type resonator by electrode pattern definition

Contour-mode piezoelectric MEMS resonators have been widely studied as one of potential components for future multi-band RF solution based on cognitive radio technology, because its resonant frequency is generally determined by the size and shape. To apply them to applications at frequency of higher than hundreds MHz, a specific higher mode should be strongly excited. However, it is often difficult, because the higher order vibration is a compound mode including radial and rotational displacements. In this study, the displacement distributions of higher order wine-glass modes of disk-type resonators were derived from FEM modal analysis. Then, mechanically-coupled disk-array filters with baseball-type and doughnut-type electrodes were fabricated and tested. Using the doughnut-type electrodes, (2. 6) mode was selectively excited, and a filter characteristic at a center frequency of 500.3 MHz was obtained. It was numerically and experimentally confirmed that a well-designed electrode pattern enhanced a specific vibration mode and suppressed other modes by comparing different electrode patterns.