Lithium Niobate Thin Film Based A3 Mode Resonators with High Effective Coupling Coefficient of 6.72%

In this paper, 600nm Z-cut lithium niobate (LiNbO
₃
) thin film based third-order antisymmetric (A3) mode resonators with different geometries has been investigated. Through a series of experiments, it has been found for the first time that effective electromechanical coupling coefficient (K
_eff
²
) is influenced by the gap between electrodes (Ge), and K
_eff
²
decreases with the increase of Ge when electrode pitch (P) higher than 5μm. Finally, a A3 mode resonator with a high 2 Keff of 6.72% is obtained. This K
_eff
²
is the highest reported value in similar acoustic resonators working about 9 GHz and will be beneficial to the construction of X-band filters.