Ultra-Wideband SH-SAW Filters Using 30° Y-cut LiNbO₃/SiO₂/Poly-Si/Si Multilayered Substrates

The rapid development of 5G wireless communication system is seeking a higher performance filters with large bandwidth and low loss. Ladder acoustic filters are widely used and can obtain large bandwidth by series and parallel combination of resonators. SH-SAW resonators based on 30°Y-cut LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>(LN)/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Si substrates exhibit a large $k_{{\text{eff}}}^2$, making it a promising candidate for designing wideband filters. However, the SH-SAW resonators with SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Si substrates still exist serious acoustic energy leakage. In this work, a SH-SAW resonator using 30°Y-cut LN/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>/Poly-Si/Si multilayered structures is proposed to obtain large $k_{{\text{eff}}}^2$. The wavelengths of the resonators are 4 µm, 4.5 µm and 6 µm, and the corresponding $k_{{\text{eff}}}^2$ are 24.4%, 22% and 21.3%, respectively. One ladder filter is composed of three series resonators at 4 µm and two parallel resonators at 4.5 µm. The filter achieves a large bandwidth (BW) of 156 MHz (FBW is 8.57%). Another filter with three series resonators at 4 µm and two parallel resonators at 6 µm is designed to obtain a larger $k_{{\text{eff}}}^2$. The BW of the filter is up to 327 MHz (FBW is 19.01%).At the same time, the band interpolation loss is deterioration as the bandwidth increases. It verifies that bandwidth and the deterioration of band interpolation loss restrict each other to a certain extent