This paper experimentally verifies the impact of thermoelastic damping (TED) in metal electrodes on the quality factor (Q _ted ) of 1 GHz Aluminum Nitride (AlN) contour mode resonators (CMRs). A semianalytical approach that treats the electrodes as standard anelastic solids and models their displacement through a 1-D wave equation is followed to predict the dependence of Q _ted on geometrical, thermal, and mechanical parameters. To verify Q _ted experimentally, resonators having top electrodes with different coverage ratios (0.75, 0.5, 0.25) and materials (Au, Pt, Al), but identical vibrating body (made out of AlN) and anchor design have been fabricated and tested. Moreover, resonators having distinct electrode metals are measured under different temperature conditions ranging from 50 to 300 K. All the experiments follow the predicted trend, which confirm that TED can be considered as the main source of intrinsic material damping in AlN CMRs and the dominant damping mechanism when anchor losses are mitigated.

This paper presents and experimentally validates two different approaches to describe the quality factor (Q) due to anchor losses in 65-MHz aluminum nitride (AlN) contour mode resonators (CMRs). The first method is an approach that can be considered qualitative in nature, as it consists of a simplified analytical model that assumes quasi-static anchor conditions and a semi-infinite substrate. Despite its simplicity, it effectively provides designers with some guidelines on how to layout resonator anchors. The second approach is quantitative and consists of a numerical technique that can be considered as an alternative to the use of perfectly matched layers (PMLs). The new finite-element method imposes fixed-constraint (FC) boundary conditions at the edges of the released regions, and the Q is calculated as the ratio of strain energy in both resonator and anchors and the total acoustic energy transferred to the substrate. The two approaches (analytical and numerical) are experimentally validated through measurements of 216 AlN CMRs operating at their fundamental resonance frequency (around 65 MHz). The proposed numerical approach is also compared with the results obtained using PML. This comparison shows that the FC technique has a similar accuracy to PML in predicting Q, but it is superior to the latter when reflections from the clamped boundaries become relevant.

This work describes a new method to enhance the electromechanical coupling coefficient (kt2) of Two-Dimensional-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 kt2, we report the design and simulated performance through Finite Element Methods of a 2.5 GHz 2DMR using metal frames. Our analysis proves that this device can simultaneously exhibit high-kt2 in excess of 6.4% and wide lithographic frequency tunability in excess of 10%, thus approaching the reported performance of AlN Film-Bulk-Acoustic-Resonators (FBARs) operating within the same frequency range.

Piezoelectric power converters, where acoustic resonators replace the inductors as energy storage elements, promise much higher power density and higher efficiency compared to conventional circuits. Recently, lithium niobate (LiNbO ₃ ) piezoelectric resonators have been integrated within power converter circuits, showing good conversion efficiency, thanks to their high quality factor ( Q ) and electromechanical coupling ( k_t² ). However, the converter output power range is limited by large spurious modes near resonance. This work reports a near-spurious-free LiNbO ₃ thickness shear (TS) resonator, demonstrating high Q of 3500 and k_t² of 45% at 5.94 MHz, with a fractional suppressed region of 35%. First, we identify the best LiNbO ₃ crystal orientation for efficient TS resonators. Then, we propose a novel acoustic design without busbars for spurious suppression, which is extensively simulated, fabricated, and characterized. Further analysis is done to identify existing spurious modes in our proposed design, specifically the effect of dicing on our TS resonator design. Upon optimization, LiNbO ₃ TS resonators could potentially empower a new design space for low-loss and compact power converters.

This work describes the implementation of acoustic metamaterials (AMs) made of a forest of rods at the sides of a suspended Aluminum Scandium Nitride (AlScN) contour-mode-resonator (CMR) to increase its power handling without causing degradations of its electromechanical performance. The increase in usable anchoring perimeter with respect to conventional CMR-designs, enabled by the adoption of two AMs-based lateral anchors, permits to achieve an improved heat conduction from the resonator’s active region to the substrate. Furthermore, thanks to such AMs-based lateral anchors’ unique acoustic dispersion features, the attained increase of anchored perimeter does not cause any degradations of the CMR’s electromechanical performance, even leading to a ~ 15% improvement in the measured quality factor. Finally, we experimentally show that using our AMs-based lateral anchors leads to a more linear CMR’s electrical response, which is enabled by a ~ 32% reduction of its Duffing nonlinear coefficient with respect to the corresponding value attained by a conventional CMR-design that uses fully-etched lateral sides.

Piezoelectric resonators promise to increase dc-dc converter power density by replacing inductive components. However, piezoelectric resonators are not direct circuit level replacements for inductors, requiring new topologies. In this paper, we present a stacked converter using two piezoelectric resonators, providing improved efficiency at low conversion ratios. This converter is realized with a lithium niobate thickness-shear mode resonator with interdigitated electrodes that allow the two resonators required for the topology to be realized as tightly matched sub-resonators on the same substrate. The 180 V to 60 V converter operates between 6.15 MHz and 6.35 MHz and achieves a resonator-level power density of $\rm {1.34}~\rm {kW}/\rm {cm}^{3}$ .