High $k_{t}^{2}$ Exceeding 6.4% Through Metal Frames in Aluminum Nitride 2-D Mode Resonators

This work describes a new method to enhance the electromechanical coupling coefficient (k
_t
²
) of 2-D mode resonators (2DMRs). This approach exploits the multimodal excitation of different Lamb waves to achieve a quasi-uniform vertical displacement distribution in the electrode regions of 2DMRs. To do so, the 2DMRs reported in this work rely on the use of metal frame structures placed at the edges of each metal strip forming the electrode gratings. To demonstrate the effectiveness of this new technique in enhancing k
_t
²
, we report the design and simulated performance through the finite-element methods of a 2.5-GHz 2DMR using metal frames. Our analysis proves that this device can simultaneously exhibit high k
_t
²
in excess of 6.4% and wide lithographic frequency tunability in excess of 10%, thus approaching the reported performance of aluminum nitride (AlN) film bulk acoustic resonators (FBARs) operating within the same frequency range.