Monolithic 1–6-GHz Multiband Acoustic Filters Using SH-SAW and LLSAW on LiNbO<sub>3</sub>/SiO<sub>2</sub>/SiC Platform
Peisen Liu, Sulei Fu, Rongxuan Su, Huiping Xu, Boyuan Xiao, Xinchen Zhou, Shuai Zhang, Rui Wang, Cheng Song, Fei Zeng, Weibiao Wang, Feng Pan
Abstract
This work presents a novel LiNbO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{3}}$</tex-math> </inline-formula> /SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf{2}}$</tex-math> </inline-formula> /SiC piezoelectric-on-insulator (POI) platform for monolithic synthesis of high-performance, multiband, and compact surface acoustic wave (SAW) filters on a single die. By means of the frequency tunability of SAW technology, simultaneous excitation of shear horizontal (SH)-SAW and longitudinal leaky SAW (LLSAW) modes that possess different velocities makes possible envisioning scalable operation frequencies (1–6 GHz). After systematical simulation, optimized 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> Y-LiNbO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textbf{3}}$</tex-math> </inline-formula> (300 nm)/SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textbf{2}}$</tex-math> </inline-formula> (200 nm)/SiC structure exhibits outstanding capabilities in delivering wideband, low-loss, and thermally stable devices. The implemented resonators show scalable resonance from 1.15 to 5.71 GHz, where a typical SH-SAW resonator exhibits a large electromechanical coupling factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k_{\textbf{eff}}^{\textbf{2}}$</tex-math> </inline-formula> ) of 24.7%, a maximum quality factor (Bode- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{max}}$</tex-math> </inline-formula> ) of 1300, and an excellent temperature coefficient of frequency (TCF) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 14 ppm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C, while the LLSAW resonator demonstrates a decent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k_{\textbf{eff}}^{\textbf{2}}$</tex-math> </inline-formula> of 14.0%, a Bode-Q <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textbf{max}}$</tex-math> </inline-formula> of 1000, and a figure of merit of 138. The fabricated filters show diverse center frequencies ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\textbf{c}}$</tex-math> </inline-formula> ) ranging from 1.77 to 5.6 GHz, 3-dB fractional bandwidths (FBWs) between 5.68% and 16.41%, a minimum insertion loss (IL) between 0.37 and 1.79 dB, an out-of-band (OoB) rejection above 25 dB, and a TCF of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\textbf{c}}$</tex-math> </inline-formula> between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 10 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 58 ppm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C. This work potentially provides a cost-effective multiband filtering solution for 5G applications.