Tunable Electromechanical Coupling Coefficient of a Laterally Excited Bulk Wave Resonator with Composite Piezoelectric Film

A resonator with an appropriate electromechanical coupling coefficient (Kt2) is crucial for filter applications in radio communication. In this paper, we present an effective method to tune the Kt2 of resonators by introducing different materials into a lithium niobate (LiNbO3) piezoelectric matrix. The effective piezoelectric coefficients e33eff and e15eff of composite materials with four different introduced materials were calculated. The results show that the e15eff of SiO2/LiNbO3 composite piezoelectric material was mostly sensitive to an increase in the width of introduced SiO2 material. Simultaneously, the simulation of a laterally excited bulk wave resonator (XBAR) with SiO2/LiNbO3 composite material was also carried out to verify the change in the Kt2 originating from the variation in e15eff. The achievable n79 filter using the SiO2/LiNbO3 composite material demonstrates the promising prospects of tuning Kt2 by introducing different materials into a LiNbO3 piezoelectric matrix.