Lithium Niobate Film Bulk Longitudinal Wave Resonator

Film bulk acoustic wave resonators (FBAR) based on LiNbO
3
single crystal piezoelectric films offer promising perspectives towards wide bandwidth filters. We present resonators based on the Y+36° crystal orientation, which promotes the excitation of longitudinal waves. This allows reaching resonance frequencies of 4.3 GHz for 600 nm-thick films, with electromechanical coupling factors of 21.4%, quality factors of 255 and impedance ratios of 245 and a temperature coefficient of frequency of -60 ppm/K, which is lower than previously reported with shear wave resonators. The resonators have also proved to withstand operation under at least 25 dBm continuous power, being limited only by the measurement setup.