Near-Spurious-Free Lithium Niobate Resonator for Piezoelectric Power Conversion with $Q$ of 3500 and k2t of 45%

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 (
$k_{t}^{2}$
). 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
$k_{t}^{2}$
of 45% at 5.94 MHz, with 0.37 MHz spurious-suppressed region. We first identify the best LiNbO
3
crystal orientation for efficient TS resonators, followed by a novel acoustic design without busbars for spurious suppression. Upon optimization, LiNbO
3
TS resonators could potentially enable new design space for low-loss and compact power converters.