FinLN: 3D Fin Lithium Niobate Acoustic Resonators

Abstract: We demonstrate a three-dimensional fin lithium niobate (FinLN) acoustic resonator fabricated from thick lithium niobate on insulator using deep ion etching and sidewall electrode patterning. The FinLN geometry enables strong three-dimensional acoustic confinement and enhanced electromechanical coupling while maintaining a compact device footprint. The fabricated devices operate near 300 MHz and exhibit an effective electromechanical coupling coefficient of 6.2% with a mechanical quality factor of 430, in good agreement with finite-element simulations. Compared to planar surface acoustic wave resonators fabricated on the same wafer, the FinLN configuration achieves an 1.8x enhancement in effective coupling. This work establishes FinLN as a promising platform for compact, high-performance RF MEMS and piezo-optomechanical systems.