A novel transducer design to enable high-performance piezoelectric MEMS resonators and oscillators

Abstract

A novel mechanism to drive pure single crystal silicon (SCS) micromechanical structure into resonance using piezoelectric transducer uniquely positioned at its support/anchor location is being reported for the first time with exceptional performance. The resonator was fabricated using MEMSCAP's PiezoMUMPs platform. This innovative method makes use of the excellent piezoelectric property of the Aluminum Nitride (AlN) thin film along with low crystal defect property of SCS, thus ensuring a very low motional impedance and high-quality factor (Q) performance. A differential drive/sense method was employed to reduce the feedthrough and eliminate spurious modes close to wine-glass (desired) mode of the SCS resonator. As a result, the designed wine-glass mode resonator operating at 21 MHz is successfully demonstrated with a motional resistance (Rm) of 1.8 kΩ and a loaded Q of 8,054 in air at 0 dBm driving power. Connecting the resonator to a lock-in amplifier with phase locked loop (PLL), a phase noise of -106 dBc/Hz at 100 Hz offset and -125 dBc/Hz at 1 kHz offset for a carrier frequency of 20.936 MHz was recorded.