A LiNbO3 A1 Lamb-wave resonator with Archimedean spiral electrodes

Abstract

Lithium niobate (LiNbO3) thin-film-based A1 Lamb-wave resonators hold significant promise for high-frequency broadband radio frequency acoustic devices because of their high phase velocity and large electromechanical coupling. Most reported devices employ straight-strip interdigital electrodes. Although this configuration is relatively mature for A1-mode excitation, there remains room for further exploration in structural topology and coordinated device-parameter design. Here, we experimentally demonstrate a suspended A1 Lamb-wave resonator based on Archimedean spiral electrodes. The proposed structure incorporates a central release window and can be extended to multiple electrode pairs and turns, thereby providing greater design flexibility. Experimental results show that a one-pair, two-turn spiral resonator based on a Z-cut LiNbO3 thin film realizes the target A1-mode resonance near 4 GHz. At a duty factor of 0.38, the device achieves an electromechanical coupling coefficient of 30.17%, a Bode-Q of 471, and a figure of merit (FoM) of 142, indicating good overall performance. In addition, extension to multi-pair, multi-turn spiral electrodes enables tunable static capacitance (C0), highlighting the potential of this configuration for the co-design of resonant unit parameters. These results indicate that the Archimedean spiral electrode provides a viable structural solution for high-frequency A1 resonators and offers new insights into the topology design and performance optimization of related devices such as filters, sensors, actuators, and antennas.