Spurious-Free Lithium Niobate Bulk Acoustic Wave Resonator with Grounded-Ring Electrode

TL;DR

This paper introduces a grounded-ring electrode design for lithium niobate bulk acoustic wave resonators that suppresses spurious modes, achieving high electromechanical coupling and quality factor for efficient energy conversion.

Contribution

It presents a novel grounded-ring electrode architecture that enables spurious-free TE-mode BAW resonators in lithium niobate, validated through simulation and experiments.

Findings

Operates at 10.14 MHz with 29.6% electromechanical coupling.

Achieves a maximum Q_Bode of 5230 and FoM of 1548.

Suppresses lateral spurious modes across the inductive band.

Abstract

High-performance piezoelectric resonators are promising energy storage elements for piezoelectric power conversion due to their compact footprint and low loss at frequencies where conventional magnetic components become bulky and inefficient. However, their practical use is often limited by the trade-off between a high electromechanical coupling coefficient (k^2) for wide-band operation and the emergence of spurious acoustic modes that limit the resonators' inductive bandwidth. This work reports a spurious-free thickness-extensional (TE)-mode bulk acoustic wave (BAW) resonator in single-crystal lithium niobate (LN) based on a grounded-ring electrode architecture. The proposed structure is analyzed through simulation and experimentally validated using electrical characterization and laser Doppler vibrometry (LDV). The results show that the grounded ring modifies the effective boundary conditions of the acoustic device, enabling a piston-like modal response that suppresses lateral spurious modes across the inductive band. The demonstrated device operates at 10.14 MHz and achieves an electromechanical coupling coefficient of 29.6%, a maximum in-band Bode quality factor (Q_Bode) of 5230, and a figure of merit (FoM, Q*k^2) of 1548. These results establish the grounded-ring TE-mode LN BAW resonator as a practical platform for piezoelectric power conversion and a broader design approach for realizing high-performance spurious-free acoustic resonators.