Wake-up behavior and early-cycle polarization degradation in ferroelectric Al0.72Sc0.28N thin films

Wurtzite-type Al1−xScxN has attracted significant attention as a next-generation ferroelectric material due to its high remanent polarization and complementary metal-oxide semiconductor-compatible growth. The physical origins of field-cycling-induced wake-up and fatigue, however, remain insufficiently understood, limiting the reliable operation of Al1−xScxN ferroelectric devices. In this work, we systematically investigate the evolution of domain dynamics and interfacial changes in Al0.72Sc0.28N films during wake-up and early-stage fatigue behaviors. The films were deposited on Pt(111)/Ti/SiO2/Si substrates by radio frequency reactive sputtering at 300 °C. By combining first-order reversal curve, Rayleigh analysis, impedance spectroscopy, x-ray photoelectron spectroscopy (XPS), and cross-sectional scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS), we show that wake-up and early-stage fatigue are associated with distinct cycling-induced processes. During the wake-up stage, the formation of opposite-polarity nuclei against the as-grown preferred polarity increases the fraction of the film participating in polarization reversal, thereby enhancing switchable polarization. At higher cycle numbers, the reduced dielectric response and increasingly inhomogeneous polarization switching are accompanied by cycling-induced defect evolution of oxygen-related processes. XPS, and cross-sectional STEM-EELS show a concurrent change in the oxygen-related spectra after electric-field cycling. Such changes may weaken the ferroelectric response, suppress field-dependent domain-wall motion, and promote the onset of fatigue. These findings highlight the importance of interface and defect engineering for improving the reliability of nitride-based ferroelectric devices.