Near 30% fractional bandwidth surface acoustic wave filters with novel electrode configuration

With the rapid progress of the wireless communication technique and the fast growing of the radio frequency (RF) markets, the development of wideband surface acoustic wave (SAW) filter is intensely pursued in RF front-end platforms. In this study, a novel configuration of SAW device was proposed in 15°YX-LiNbO3 (300 ​nm)/SiO2 (600 ​nm)/Si heterostructure, where the series and shunt resonator innovatively adopt Cu electrodes of different thickness to suppress the unwanted Rayleigh mode efficiently. Series and shunt resonators with clean spectrum and high electromechanical coupling coefficients over 20% were experimentally achieved under the guidance of finite element method calculation. Based on the resonator results, a ladder-type SAW filter with a very large 3-dB fractional bandwidth near 30% was successfully designed and fabricated. The minimum insertion loss of device is as small as 1.1 ​dB while the in-band fluctuation is less than 0.3 ​dB. The unprecedented wideband property of SAW device indicates that the proposed configuration is expected to become one of the solutions of wideband filter in fifth-generation mobile communication, and possess great commercial application prospects.