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

This work presents a novel LiNbO3/SiO2/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° Y-LiNbO3 (300 nm)/SiO2 (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 (
$k_{\textbf {eff}}^{\textbf {2}}$
) of 24.7%, a maximum quality factor (Bode-
${Q}_{\text {max}}$
) of 1300, and an excellent temperature coefficient of frequency (TCF) of −14 ppm/°C, while the LLSAW resonator demonstrates a decent
$k_{\textbf {eff}}^{\textbf {2}}$
of 14.0%, a Bode-
${Q} _{\textbf {max}}$
of 1000, and a figure of merit of 138. The fabricated filters show diverse center frequencies (
${f}_{\textbf {c}}$
) 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
${f}_{\textbf {c}}$
between −10 and −58 ppm/°C. This work potentially provides a cost-effective multiband filtering solution for 5G applications.