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 LiNbO₃ 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 LiNbO₃-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 LiNbO₃ thin-film acoustic devices.