Finite Element Modeling and Synthesis of c-axis Tilted AlN TFBAR for Liquid Sensing Applications

Thin film bulk acoustic resonator (TFBAR) with c-axis tilted AlN finite element modeling was performed using COMSOL Multiphysics simulation software. Depending on the AlN c-axis tilt angle, dual mode TFBAR can be obtained that operate in longitudinal and shear mode: the former mode is a thickness-extensional mode, while the latter is a thickness-in plane-shear mode that is suitable for liquid sensing applications. The acoustic wave displacement, the resonator frequency and equivalent admittance of the TFBARs with different tilt angles and electrode thicknesses were simulated to obtain the optimum design (high electroacoustic coupling efficiency and large quality factor Q) for shear mode operation. Furthermore, AlN films having the c-axis tilted up to about 30? from the substrate normal were successfully grown on silicon (100) substrates by reactive rf magnetron sputtering technique at 200?C.