Monolithic 1–6-GHz Multiband Acoustic Filters Using SH-SAW and LLSAW on LiNbO₃/SiO₂/SiC Platform

This work presents a novel LiNbO <tex-math notation="LaTeX">₃</tex-math> /SiO <tex-math notation="LaTeX">₂</tex-math> /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 <tex-math notation="LaTeX">∘</tex-math> Y-LiNbO <tex-math notation="LaTeX">₃</tex-math> (300 nm)/SiO <tex-math notation="LaTeX">₂</tex-math> (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 ( <tex-math notation="LaTeX">keff²</tex-math> ) of 24.7%, a maximum quality factor (Bode- Q <tex-math notation="LaTeX">ₘₐₓ</tex-math> ) of 1300, and an excellent temperature coefficient of frequency (TCF) of <tex-math notation="LaTeX">$-$</tex-math> 14 ppm/ <tex-math notation="LaTeX">∘</tex-math> C, while the LLSAW resonator demonstrates a decent <tex-math notation="LaTeX">keff²</tex-math> of 14.0%, a Bode-Q <tex-math notation="LaTeX">ₘₐₓ</tex-math> of 1000, and a figure of merit of 138. The fabricated filters show diverse center frequencies ( <tex-math notation="LaTeX">fc</tex-math> ) 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 <tex-math notation="LaTeX">fc</tex-math> between <tex-math notation="LaTeX">$-$</tex-math> 10 and <tex-math notation="LaTeX">$-$</tex-math> 58 ppm/ <tex-math notation="LaTeX">∘</tex-math> C. This work potentially provides a cost-effective multiband filtering solution for 5G applications.