High figure of merit for acoustic resonators at tens to hundreds of GHz

Establish methods to achieve relatively high figures of merit, defined as the product of electromechanical coupling (k2) and quality factor (Q), in electrically driven thin-film acoustic resonators operating in the tens to hundreds of gigahertz, overcoming the degradation of electromechanical coupling in high-order modes and the increased defect density and surface damping in thinner piezoelectric films.

Background

The paper defines the figure of merit for acoustic resonators as k2Q and highlights that pushing resonator operation to millimeter-wave frequencies typically requires thinner films or higher-order modes. Thinner films suffer increased defects and surface damping, reducing Q and k2, while higher-order modes experience electromechanical coupling cancellation due to strain-field mismatch.

The authors motivate their multilayer lithium niobate approach by noting that achieving high k2Q at tens to hundreds of GHz is challenging. Alternating crystallographic orientations across layers is proposed to constructively align strain and electric fields, potentially enhancing k2 without sacrificing Q.