Wideband and Low-Loss Surface Acoustic Wave Filter Based on 15° YX-LiNbO₃/SiO₂/Si Structure
Rongxuan Su, Junyao Shen, Zengtian Lu, Huiping Xu, Qingshan Niu, Zhibin Xu, Fei Zeng, Cheng Song, Weibiao Wang, Sulei Fu, Feng Pan
Abstract
With the development of the radio frequency technique, the explosive growth of transmitted data in 5G era puts higher requirements on surface acoustic wave (SAW) filter bandwidth. In this work, 15°YX-LiNbO3(LN)/SiO2/Si multilayer structure was proposed, where both LN and SiO2 films possess uniform thickness and the interfaces between films are quite clear. With hierarchical cascading algorithm, the spurious resonance that resulted from Rayleigh mode was minimized through the modulation of Cu electrode thickness. One-port resonators measurement results confirm a high electromechanical coupling coefficient of shear horizontal mode ranging from 22.5% to 25.2%. Furthermore, a ladder-type filter with a center frequency of 1279 MHz and a large fractional bandwidth of 20.2% was successfully fabricated. Excellent bandpass filtering properties were achievable with minimum insertion loss of 0.8 dB and in-band fluctuation less than 0.9 dB. Multilayer structure SAW filters also exhibited a temperature coefficient of frequency of -57.7 ppm/°C and a power durability of 33 dBm, which are both significant improvements compared with that of devices built on bulk 15°YX-LN substrate. This work provides an effective solution for wideband and low-loss radio frequency filters in 5G communication systems, suitable for large-scale application and commercial promotion.