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 degrees Y-cut LiNbO3(LN)/SiO2/Si substrates exhibit a large k(eff)(2), making it a promising candidate for designing wideband filters. However, the SH-SAW resonators with SiO2/Si substrates still exist serious acoustic energy leakage. In this work, a SH-SAW resonator using 30 degrees Y-cut LN/SiO2/Poly-Si/Si multilayered structures is proposed to obtain large k(eff)(2). The wavelengths of the resonators are 4 mu m, 4.5 mu m and 6 mu m, and the corresponding k(eff)(2) are 24.4%, 22% and 21.3%, respectively. One ladder filter is composed of three series resonators at 4 mu m and two parallel resonators at 4.5 mu m. The filter achieves a large bandwidth (BW) of 156 MHz (FBW is 8.57%). Another filter with three series resonators at 4 mu m and two parallel resonators at 6 mu m is designed to obtain a larger k(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