Aluminum Nitride-Based Adjustable Effective Electromechanical Coupling Coefficient Film Bulk Acoustic Resonator.

The arrival of the 5G era has promoted the need for filters of different bandwidths. Thin-film bulk acoustic resonators have become the mainstream product for applications due to their excellent performance. The K eff 2 of the FBAR greatly influences the bandwidth of the filter. In this paper, we designed an AlN-based adjustable K eff 2 FBAR by designing parallel capacitors around the active area of the resonator. The parallel capacitance is introduced through the support column structure, which is compatible with conventional FBAR processes. The effects of different support column widths on K eff 2 were verified by finite element simulation and experimental fabrication. The measured results show that the designed FBAR with support columns can achieve a K eff 2 value that is 25.9% adjustable.