Strain Engineering on Lithium Niobate Crystal Based SAW Resonators Through Ion Implantation

In this work, a novel quasi-heterostructure consisting of a shallow surface layer of strained LiNbO3 and a virgin LiNbO3 substrate is demonstrated. The quasi-heterostructure is constructed by implanting helium ions into the surface layer of a single-crystalline X-cut LiNbO3 wafer, where the material properties of the surface layer will be modulated by the implanted ions. The X-ray diffraction (XRD) rocking curves were measured to characterize the crystalline quality and strain distribution of the ion-implanted layer. The Rayleigh-SAW resonators on the quasi-heterostructure and virgin LiNbO3 were fabricated. The resonators on the quasi-heterostructure exhibit higher resonance frequencies (1.15-1.17 times), larger electromechanical coupling factors (1.1-1.4 times), higher quality factors (1.1 times), and larger static capacitances (1.33 times), indicating that the elastic constants, piezoelectric constants, and dielectric constants of the strained LiNbO3 layers have been effectively modulated. Although the correlations between the improved performances and the modulated material constants are still under study, the improvements reveal the feasibility of performance modulation of SAW resonators by strain engineering.