Capacitive-piezoelectric AlN resonators with Q>12,000

A “capacitive-piezo” transducer that separates a piezoelectric resonator from its electrodes via small gaps to eliminate resonator-to-electrode loss while maintaining strong electromechanical coupling, has enabled demonstration of a 50-MHz wine-glass disk (WGD) resonator array with Q=12,748. This is higher than exhibited by any sputtered thin-film AlN resonator measured to date at any frequency and more than 2.2× larger than previously achieved by similar devices using conventional (i.e., contacting) electrodes. By attaining such high Q, this work erases a common belief that material losses in sputtered AlN dominate the Q's of resonators constructed in this material and confirms that sputtered AlN is a high-Q material. It further suggests that energy loss associated with contacting electrodes is primarily responsible for the low Q's of previous AlN resonators. With Q's over 10,000, this work identifies AlN as a viable material for use in channel-selecting RF front ends targeted for future software-defined cognitive radio.