Near Spurious-Free Thickness Shear Mode Lithium Niobate Resonator for Piezoelectric Power Conversion

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 (LiNbO3) piezoelectric resonators have been integrated within power converter circuits, showing good conversion efficiency, thanks to their high quality factor (
${Q}$
) and electromechanical coupling (
${k}_{t}^{\,{2}}$
). However, the converter output power range is limited by large spurious modes near resonance. This work reports a near-spurious-free LiNbO3 thickness shear (TS) resonator, demonstrating a high
${Q}$
of 3500 and
${k}_{t}^{\,{2}}$
of 45% at 5.94 MHz, with a fractional suppressed region of 35%. First, we identify the best LiNbO3 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, LiNbO3 TS resonators could potentially empower a new design space for low-loss and compact power converters.