Twist Piezoelectric Coupling Properties to Suppress Spurious Modes for Lithium Niobate Thin-film Acoustic Devices

This paper presents a new method to suppress spurious modes in lithium niobate thin-film acoustic devices by twisting the piezoelectric coupling properties of the spurious modes. The excellent piezoelectric properties of lithium niobate (LiNbO3) advance performance but lead to significant spurious modes accompanied by the targeted main mode. To harvest the benefits and avoid the spurious modes, this work investigates solidly mounted LiNbO
3
thin films with different substrates to twist the zero-coupling orientations of spurious modes to be close to the maximum-coupling orientation of the targeted main mode. The fabricated devices, based on the solidly mounted LiNbO
3
-sapphire structure and surface guided acoustic wave, show an operating frequency of 2.4 GHz with a large electromechanical coupling of 22% and a spurious-free response in the wide frequency range. This work could overcome a significant bottleneck in commercializing LiNbO
3
thin-film acoustic devices.