Influence of Etching Trench on Keff2 of Film Bulk Acoustic Resonator

As radio-frequency (RF) communication becomes more ubiquitous globally, film bulk acoustic resonators (FBAR) have attracted great attention for their superior performance. One of the key parameters of an FBAR, the effective electromechanical coupling coefficient (K-eff(2)), has a great influence on the bandwidth of RF filters. In this work, we propose a feasible method to tune the K-eff(2) of the FBAR by etching the piezoelectric material to form a trench around the active area of the FBAR. The influence of the position of the etching trench on the K-eff(2) of the FBAR was investigated by 3D finite element modeling and experimental fabricating. Meanwhile, a theoretical electrical model was presented to test and verify the simulated and measured results. The K-eff(2) of the FBAR tended to be reduced when the distance between the edge of the top electrode and the edge of the trench was increased, but the Q value of the FBAR was not degraded. This work provides a new possibility for tuning the K-eff(2) of resonators to meet the requirements of different filter bandwidths.

Automated summary

As radio-frequency communication becomes more common, film bulk acoustic resonators (FBAR) have attracted attention for their superior performance. This study proposes a method to tune the FBAR's performance by etching the piezoelectric material, and investigates the effect of etching trench position on the FBAR's properties.