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Fully-differential AlN-on-Si wine glass mode resonator for enhanced characterization in water

In this work, we present a fully-differential wine-glass (WG) mode MEMS resonator fabricated in thin film Aluminum Nitride (AlN) on Silicon (Si) MEMS technology for resonant sensing applications in liquids. Our finite element (FE) simulations show that the strain fields associated with this mode are well suited for fully-differential piezoelectric transduction. We experimentally demonstrate that the WG mode consequently possesses strong electromechanical coupling. We have also measured the highest quality factor in water among various contour mode resonators yet with a value of 360. But the notably high dielectric constant of liquids like water introduces a large amount of feedthrough in the electrical characterization of the resonators. To this end, we show that the fully-differential configuration is highly effective in reduction feedthrough. The simultaneous enhancement of the resonant signal and reduction in background using the WG mode allows us to achieve a signal to background ratio (SBR) of 15 dB.