Piezoelectric resonant MEMS balances with high liquid phase Q

This work presents low motional resistance piezoelectric MEMS resonators with the highest quality factor (Q) in water reported to date that can be used for direct biomarker or chemical detection in liquid media. Thin film Piezoelectric-on-substrate (TPoS) resonators operating in higher order lateral bulk acoustic modes are designed and fabricated, and their performance as mass balances in water is characterized. Q up to 312 and motional resistance as low as 662Ω were measured in water for devices with resonant frequency of 11MHz. To characterize resonator mass sensitivities, a SiO₂ passivation layer on top of one of the resonators was slowly etched in several consecutive steps and frequency shifts were recorded showing of 33.4 cm²/ng. Higher order mode operation and relatively large size of the devices (high volume/surface ratio) along with wide gaps between the resonating body and the substrate are considered to be the main factors minimizing viscous damping in liquid.