High Overtone Mode Solid Mounted Resonators with Polarity Inverted Multilayered SiAlN/AlN Films

High frequency bulk acoustic wave (BAW) resonators are required for next-generation communication applications. Polarity inverted multilayered film BAW resonators resonate strongly in the high-overtone mode. Therefore, they can operate at higher frequency and have larger device volume, resulting in higher power handling capability, than standard single-layer film BAW resonators. In this study, we fabricated the polarity inverted multilayered SiAlN/AlN film solid mounted resonators (SMRs) operating around 5 GHz. To fabricate two-layer polarity inverted film SMRs, the Al-polar AlN films and the N-polar SiAlN films were grown as the odd layers and the even layers, respectively, on the acoustic Bragg mirror substrates. Strong AlN (0002) peaks were observed in the 2θ-θ XRD patterns of the films. The two-layer polarity inverted SiAlN/AlN film SMRs resonated strongly in the second-overtone modes around 5 GHz. The Q values of the SMRs increased with increasing the number of polarity inverted layers. On the other hand, the $k_{{\text{eff}}}^2$ of the SMRs were almost the same at approximately 4%.