Analysis and design of coupled resonator filters with a single coupling layer

Bulk acoustic wave coupled resonator filters with a single coupling layer between resonators are a promising option to fabricate this kind of miniaturized filters because of its simpler fabrication process than a multilayer coupling structure. Very low acoustic impedance materials are needed to achieve suitable couplings between the stacked resonators. Advances in FBAR materials and technologic processes are making possible to implement this single layer successfully. Due to the fixed impedance of the coupling layer, its thickness is the variable that controls the coupling interaction between resonators. The coupling layer does not work as a coupler by itself, but part of the resonators contributes to the coupling. Those considerations must be taken into account during the filter design process to obtain arbitrary filter responses. This work presents the steps of a whole design of one coupled resonator filter with a single coupling layer and analyzes the functions that the different parts of the structure perform in the filtering device.