Unveiling the Dispersive Nature of Periodically Poled Al(Sc)N-Based Bulk Acoustic Wave Resonators

Bulk acoustic wave (BAW) resonators with periodically poled piezoelectric films (P3F) are highly promising for super high frequency (SHF) in 5G and the emerging 6G radio frequency (RF) applications. Despite their potential, the dispersion relationship of P3F Al(Sc)N-based BAW resonators has not been systematically explored, which remains one of the most crucial device physics for understanding and engineering device resonant characteristics. This work presents a comprehensive investigation into the dispersion behaviors of BAW resonators fabricated with periodically poled AlN/AlN and AlN/Al0.7Sc0.3N stacks designed for Ku-band operation. Our analysis reveals the Type I dispersive nature of the second thickness-extension (TE2) mode. Furthermore, we establish a direct correlation between this dispersion and the presence of spurious resonances, providing crucial insight into their origin. To further optimize performance, we fabricated resonators with a frame structure, which demonstrated a significantly enhanced quality factor. Moreover, the major intrinsic acoustic dissipation mechanisms of P3F Al(Sc)N-based BAW acoustic devices are systematically investigated. Taken together, our findings on dispersion, spurious modes, and dissipation mechanisms provide a foundational understanding of periodically poled Al(Sc)N BAW resonators, which points to a pathway toward optimizing next-generation acoustic devices for high-frequency applications.