Gaussian Focused-Cavity Resonator

Contour mode resonators in suspended AlN films experience performance limitations from anchors and bussing. To mitigate this, we show how confocal acoustical resonators designed with tailored electrode shapes increase quality factor by concentrating the mode energy toward the resonator center, focusing the cavity mode away from anchors, while also maintaining coupling coefficient even with extremely tight focusing. We present a theoretical treatment for electrode design and present an experimental analysis comparing straight fingered vs focused cavity, showing both a Q increase and constant coupling coefficient while the radius of curvature is increased from loose focusing to the diffraction limit.