Design and simulation of coupled-resonator filters using periodically slotted electrodes on FBARs [Correspondence]

This paper discusses the use of periodically slotted top electrodes in the film bulk acoustic resonator (FBAR) structure for the realization of wideband coupled-resonator filters (CRFs), where evanescent modes in the periodic structure are used for the coupling between adjacent electrodes. First, wave propagation in this structure is investigated. Finite element analysis is performed for the Mo/ZnO/Mo structure. The result suggests that lateral wave propagation is controlled by the Bragg reflection, and that transverse modes can be suppressed when the structure is properly designed. Next, a CRF is designed. It is shown that wideband CRFs are realizable when the period, thickness, and width of slotted electrodes are properly set.