Improving Thermal Linearity and Quality Factor of Al₇₂Sc₂₈N Contour Mode Resonators Using Acoustic Metamaterials based Lateral Anchors

In the last years, the use of Scandium-doped AlN (AlScN) as the active material in piezoelectric resonators has been investigated by many research groups thanks to its high piezoelectric coefficients and its CMOS manufacturability. However, because of the AlScN’s low thermal conductivity, any AlScN resonators inherently exhibit lower power handling than the AlN counterparts, especially when such resonators are required to be suspended in order to operate. Even more, while the adoption of larger anchors in conventional AlScN resonators enable higher power handlings, it comes with an unsustainable reduction of the resonators’ quality factors (Qs). In this work, we overcome this limitation. We show that the adoption of acoustic metamaterials made of locally resonant rods at the sides of a suspended contour-mode-resonator (CMR) permits to largely increase the usable anchoring volume with respect to conventional CMR designs, enabling improved heat flows from the resonator’s active to the inactive regions and, consequently, a higher thermal linearity. Furthermore, thanks to the unique dispersion features of the adopted metamaterial structure, the use of a significantly more robust anchoring strategy does not lead to any degradations of the CMR’s electromechanical performance, even leading to a ~25% improvement in the measured Q.