A 6.5-GHz Interdigital-Metal-Oxide Lamb Wave Resonator with Near-Zero TCF and High Electromechanical Coupling Coefficient of 20.4%

This paper reports on a S2-mode interdigital-metal-oxide Lamb wave resonator (IMO-LWR), addressing the need for low frequency temperature coefficient (TCF) in lithium niobate (LN) for high-frequency applications. The proposed solution targets 5G/6G and millimeter-wave communication demands. Firstly, we analyze the electromechanical coupling coefficient (k²) of Lamb wave modes versus the SiO2/LN thickness ratio, identifying the S2 mode with maximum k² at a 1:1 ratio. Then, the impact of substrate materials on LN’s thermal expansion coefficient (CTE) and TCF is simulated. Finally, device fabrication and measurement results are given in detail. The fabricated device excites S2 mode Lamb waves in the SiO2/LN stack, achieving near-zero TCF and a high k² of 20.4% at 6.5 GHz, surpassing conventional LN resonator performance.