Reduction of Motional Resistance Using Piezoelectric on Silicon MEMS Disk Arrays for Ambient Air Applications

This paper presents the implementation of a piezoelectric contour resonance mode in a micro-electro-mechanical (MEM) disk resonator array, fabricated using a low-cost, commercially available MEMS technology. The resonator operates in a Button-like (BL) mode, which is suitable for a fully differential piezoelectric transduction mechanism. Compared to other modes, such as the anti-symmetric (AS) mode and the Higher wine glass (HWG) mode, the BL mode offers a higher quality factor (Q) and a reasonable coupling coefficient (k_t²) for the same perimeter around the disk device. The mechanical coupling and excitation of a parallel array of nodal point-coupled piezoelectric disk resonators significantly reduce the motional resistance (R_m) of the vibrating disk MEMS resonator, making the BL mode highly attractive due to the achieved performance improvements. The implementation of this method with three resonators results in an effective motional resistance of 101Ω at 32 MHz under ambient air conditions. This value is approximately 3.9 times lower (Q_ul normalized) than the R_m of 822Ω exhibited by a single contour mode disk resonator. Additionally, an unloaded quality factor (Q_ul) of 8,230 is observed when operating at 0 dBm power in ambient air. Notably, these enhancements are achieved while maintaining an effective Q_ul> 10,000, as measured in vacuum conditions, along with notable power-handling capabilities in both ambient air and vacuum environments. This work also investigates two other contour resonance modes with the same design considerations to further validate the proposed methodology.