Sensing characteristics of pure-shear film bulk acoustic resonator in viscous liquids

We presented a pure-shear film bulk acoustic resonator (FBAR) and investigated its sensing characteristics in viscous liquids. In the resonator, the electrodes were located on the surface of c-axis-oriented AlN film to generate the lateral electric field and excite the shear acoustic resonance. Compared with the typical quasi-shear film bulk acoustic resonator based on inclined c-axis-oriented AlN or ZnO piezoelectric film, the proposed device exhibits significantly higher Q-factors and a notably improved detection limit, particularly in water and viscous liquids. The frequency shifts show a linear dependency on the square root of the product of the liquid viscosity and density of the glycerol solution in the viscosity range of 1–5 mPa⋅s. Furthermore, we measured the mass sensitivity through real-time monitoring of the frequency change during the volatilization process of the loaded saline solutions. The proposed device shows the mass sensitivity of 465 Hz⋅cm2/ng and the mass resolutions of 0.17 ng/cm2 in...