Enhancement of coupling factor in 0th to 4th mode Rayleigh surface acoustic waves on polarity inverted multilayered ScAlN film/AlN and BN substrates

Abstract

Abstract The rapid development of mobile communications requires high performance surface acoustic wave (SAW) filters. ScAlN film SAW resonators have a high coupling factor (K 2) and high phase velocity, enabling them to function as effective SAW filters. We theoretically investigated high-order mode Rayleigh SAWs (RSAWs) on single-layered or polarity inverted two-layered ScAlN film/AlN or BN substrate structures to find the optimal structure to achieve a higher K 2 and higher frequency. The K 2 and phase velocity for the single-layered ScAlN film/BN substrate structure were higher than those for the corresponding AlN substrate structure. The K 2 was enhanced in the polarity inverted ScAlN film/AlN or BN substrate structure. Finite element method analysis revealed that the effective coupling factor K eff 2 for the 2nd to 4th mode RSAWs on polarity inverted multilayered ScAlN films was enhanced by setting the boundary of the polarity inverted structure at the all positions where the particle displacements were concentrated.