Impact of FBAR design on its sensitivity as in-liquid gravimetric sensor

Abstract

In contrast to quartz crystal microbalances, the sensitivity of thin film bulk acoustic wave resonators (FBARs) is strongly dependent on all films comprising the multilayered structure. Previous studies proved that placing low acoustic impedance materials at the sensing surface of longitudinal-mode FBARs operating in air can enhance their mass sensitivity by modifying the energy trapped at the sensing surface. Here we investigate if the in-liquid sensitivity to density-viscosity and mass of shear-mode AlN-based solidly mounted resonators displays a similar dependence on the device configuration. By using the finite element simulation method accompanied by experimental verifications we demonstrate that for a given value of the resonant frequency, the sensitivity can be boosted by a proper design of the devices. The results can be of application to in-liquid physical sensors or to gravimetric chemical or biological sensors.