Optical loss characterization and analysis of wafer-scale scandium-doped AlN photonic devices

Scandium-doped aluminum nitride (ScAlN) is a promising material for CMOS-compatible photonic platforms due to its improved material properties and compatibility with wafer-scale processes. In this work, we report the optical loss characteristics of 10% ScAlN thin films deposited via co-sputtering on 8-inch wafers. In addition to device-level characterization, the material properties of the ScAlN films are systematically examined, including top surface roughness measured by atomic force microscopy and optical constants extracted from spectroscopic ellipsometry. Propagation losses are extracted from microring resonators with varying waveguide dimensions, showing a clear trend of increasing loss with larger waveguide width and thickness. This behavior is primarily attributed to increased optical absorption due to mode confinement and variations in material quality. Wafer-level measurements further reveal that waveguides located near the wafer edge exhibit lower losses than those at the center, suggesting improved crystallinity and reduced defect density at the periphery. These results highlight the potential of ScAlN for low-loss, scalable photonic integration.