Piezoelectric-on-silicon square wine-glass mode resonator for enhanced electrical characterization in water

We describe a piezoelectric square wine-glass (SWG) mode micromechanical resonator as a unique device topology for liquid phase sensing applications that offers enhanced quality (Q)-factor in water over other common contour modes. We show a Q-factor in water of 377 for 14.08-MHz SWG mode resonator (mean of multiple measurements), which is one of the highest Q-factors among piezoelectric resonators tested when covered in a fluid. We show that the Q-factor in water of the SWG mode increases much more significantly with a reduction in resonator size relative to the square-extensional (SE) mode, such that the Q-factor the SWG mode can be almost twice of the SE mode. We present an analytical model for the mode shape of the proposed SWG resonators and their effective electromechanical coupling factor (k²_eff). Due to the enhanced Q-factor in water, reasonable k²_eff, and feedthrough cancelation (using fully differential transduction with the fluid loaded from the backside of the device), we show that a strong resonant peak of 29.8 dB is obtainable in water.