High-Q Shear Mode ZnO-based Film Bulk Acoustic Resonators with Air Cavity for Liquid-Phase Sensing Applications

In recent years, demand has surged for liquid-phase sensors in the healthcare industry, enabling remote early diagnosis, testing, and monitoring of patients. Acoustic sensors have become the most efficient solution for bio-sensing due to their unique characteristics, such as high sensitivity, small size, low power requirement, high specificity, high selectivity, high stability, low cost, and low insertion loss. Therefore, this paper presents a comprehensive two-dimensional finite element analysis (FEA) of shear-mode film bulk acoustic resonators (FBARs) to optimize their performance for liquid detection. The radio frequency (RF) measurement of a shear-mode acoustic resonator has been performed for the fabricated device. The bulk zinc oxide was deposited on the oxide support layer using the RF sputtering method. Further, a pair of coplanar gold electrodes was deposited on the ZnO layer. The surface morphology of bulk ZnO have been studied using Field Emission Scanning Electron Microscopy (FESEM) and atomic force microscopy (AFM) techniques. The surface roughness and grain size of ZnO grown on SiO2 layer has been estimated to be 5.2 nm and 114 nm, respectively. The return loss spectra depict that the resonator has a central frequency (f0) of 2 GHz with –3 dB bandwidth (1.0386 MHz) and a return loss (S11) of –15.72 dB.