Periodically Poled Piezoelectric Lithium Niobate Resonator for Piezoelectric Power Conversion.

As demand for compact and efficient power conversion systems increases, piezoelectric power converters have attracted attention for their ability to replace bulky magnetic inductors with acoustic resonators, thereby enabling higher power density and improved efficiency. Achieving optimal converter performance requires resonators with a high quality factor (Q), strong electromechanical coupling ( $\textit {k}^{{2}}$ ), high-power handling capability, and a spurious-free response. Lithium niobate (LN) has emerged as a promising material in this context due to its high figure of merit (FoM $= \textit {Q} \cdot \textit {k}^{{2}}$ ). While previous studies on single-layer LN resonators have demonstrated high FoM values, they typically operate at relatively low resonance frequencies ( $\textit {f}_{\textit {s}}$ ). Recently, periodically poled piezoelectric film (P3F) structures, formed by stacking piezoelectric layers with alternating crystal orientations, have shown the potential to both scale up the operating frequency and enhance the FoM compared to single-layer counterparts in piezoelectric power conversion. This work presents the first P3F thickness-extensional (TE) LN resonator for power conversion, operating at 19.23 MHz, with a large $\textit {k}^{{2}}$ of 29% and a high maximum Bode Q of 3187, achieving a state-of-the-art ( $\textit {f}_{\textit {s}} \cdot \textit {Q}$ ) product among piezoelectric power resonators. A high-power testing procedure is employed to systematically investigate the nonlinear behavior and power-handling capabilities of P3F LN for power applications. With further optimization, P3F TE resonators have the potential to enable a new design space for high-power, high-frequency power conversion.