Cross-Sectional Láme Mode Acoustic Resonators in Thin-Film Lithium Niobate

In this work, we demonstrate first-of-its-kind, cross-sectional Láme mode resonators (CLMR) in thin-film lithium niobate (LN) at 6G FR3 frequency bands. The prototype LN CLMR exhibits two cross-sectional Láme mode (CLM) resonances due to its unique working mechanism, showing high 3-db parallel quality factors $(\!Q_{p}\!)$ of 225 and 398 at 13.9 and 14.9 GHz, alongside a high extracted electro-mechanical coupling ( $k^{2}$ ) of 13.4% and 7.2%, respectively. These results yield high figures of merit (FoM, $Q_{p}$ $\cdot $ k² ) of 30.2 and 28.7 at their operating frequencies. In comparison with conventional fundamental symmetric (S0) Lamb mode resonators on the same sample, the proposed platform scales its S0 counterpart in frequency while showing higher Q, highlighting the low-loss property of the cross-sectional Láme mode (CLM). With further fabrication optimization, a new family of cross-sectional modes can be characterized, warranted by the strong dispersive nature of LN, disrupting the status quo in single-crystal LN device design.