Q Enhancement and TCF Reduction for Piezoelectric MEMS Resonators via Mechanical Coupling

This work demonstrates an effective approach to enhance the quality factor (Q) and reduce the temperature coefficient of frequency (TCF) for piezoelectric MEMS resonators via mechanical coupling. The reported resonator is composed of two identical single-crystal silicon (SCS) disks coupled by a SCS rectangle plate with piezoelectric stacks positioned above. During operation, the plate is piezoelectrically excited into vibrating in width-extensional (WE) mode and two disks are forced into vibrating in radial breathing (RB) mode by mechanical coupling. The plate and two disks could be viewed as two types of individual resonators. Although theQandTCFof them are quite different due to the mode difference and the presence of piezoelectric stacks on the plate, they can vibrate synchronously under the same resonant frequency at proper given sizes. Hence, theQandTCFof the coupled resonator could be manipulated by adjusting the effective mass ratio between two coupling parts. Experiment results illustrate that the fabricated coupled resonator resonates at 25.202 MHz with an unloadedQof 80695 and frequency shifts of ±55 ppm over the temperature range of −40 °C to 85 °C. Compared to a standalone WE resonator fabricated under the same conditions, this represents a 2.44-fold increase inQᵤₙand a 2.5-fold reduction in frequency drifts, underscoring the effectiveness of the mechanical coupling approach in optimizing resonator performance. [2025-0077]