Low-Loss N79 Band SAW Filter With 16.0% FBW Based on15° <i>Y-X</i> LiNbO₃/SiC Structure

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).