FBAR laterally Coupled Resonator Filter

A very attractive CRF (Coupled Resonator Filter) topology is to laterally couple thin film bulk acoustic resonators (FBAR). However, the filter band width is narrow because the coupling between conventional FBAR resonators is very weak. The coupling, and thus the bandwidth, may be increased by forming pairs of FBAR with an inter-digital coupling configuration. Both narrow electrode finger width and multiple coupled finger pairs enhance lateral acoustical coupling, resulting in filters with wider pass band. The finite element simulation and experimental results on LCRF structures show that the multiple acoustical modes can be combined to form a wider range of pass bands than available in a conventional ladder filter.