Fully Differential Piezoelectric Button-Like Mode Disk Resonator for Liquid Phase Sensing

We present a unique lateral shear resonance mode excited in a microelectromechanical (MEM) disk resonator. We refer to this proposed mode as the button-like (BL) mode. The BL mode has a characteristic lateral strain profile (based on the sum of orthogonal strain components in the plane of fabrication) which resembles a shirt button, hence our choice of name for this mode. The strain profile of the BL mode is highly suited for piezoelectric transduction. Like the more widely reported wine-glass (WG) or elliptical mode, the BL mode offers feedthrough cancellation through fully differential transduction. However, compared to the WG mode, the BL mode possesses a higher coupling coefficient ( {k}_{\text {eff}}^{2} ) and a higher quality ( Q ) factor for the same disk radius. These advantages make the BL mode highly attractive for realizing electrically addressed MEM resonators for liquid-phase sensing. This paper examines various design aspects pertaining to the BL mode: tether geometry, characterization setup, size of disk, and even the effect of the gap around the disk on the Q factor. The highest Q factor measured in water is 410 based on a disk with a radius of 150~\mu \text{m} . The lowest motional resistance in water is 1.36 \text{k}\Omega based on a disk with a radius of 400~\mu \text{m} .