Low-Loss N79 Band SAW Filter With 16.0% FBW Based on15° <i>Y-X</i> LiNbO₃/SiC Structure
Huiping Xu, Sulei Fu, Rongxuan Su, Peisen Liu, Boyuan Xiao, Xinchen Zhou, Qiufeng Xu, Shuai Zhang, Ruikang K. Wang, Cheng Song, Fei Zeng, Weibiao Wang, Feng Pan
Abstract
Surface acoustic wave (SAW) filters with improved frequency and bandwidth are highly demanded in the 5G system to cater for the high-throughput wireless communication. This work demonstrates a low-loss SAW filter using shear horizontal (SH) mode in 15° Y-X LiNbO3 (LN)/SiC heterostructure, successfully covering full n79 band. Resonators were investigated theoretically and experimentally to optimize the designing parameters of LN film. The measured resonators with varying LN thickness (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${h}_{\text {LN}}\text {)}$ </tex-math></inline-formula> exhibit scalable resonant frequencies from 4478 to 5239 MHz with high phase velocity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {p}}\text {)}$ </tex-math></inline-formula> over 4200 m/s, large coupling coefficient (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}^{{2}}\text {)}$ </tex-math></inline-formula> between 16.0% and 28.3% and near spurious-free response. The fabricated filter shows a center frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {c}}\text {)}$ </tex-math></inline-formula> of 4693 MHz, a 3-dB fractional bandwidth (FBW) of 16.0%, a minimum insertion loss (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {IL}}_{\min }$ </tex-math></inline-formula>) of 0.70 dB and an out-of-band rejection of 17.8 dB. This is the first report of a SAW filter covering n79 full band, which can provide a valuable reference for advancing SAW application in 5G new radio (NR).