Robust low-temperature ferroelectric behavior of Al0.75Sc0.25N films

Abstract

Al1−xScxN, which combines excellent ferroelectric properties with the advantages of wide-bandgap nitride materials, offers emerging opportunities for breakthroughs in next-generation microelectronics. Maintaining the high ferroelectric performance of Al1−xScxN far from room temperature can further broaden its applications in extreme environments. However, its cryogenic ferroelectricity has not been revealed yet. Therefore, this study focuses on the low-temperature stability of Al0.75Sc0.25N films. From 20 to −150 °C, the film retains a stable wurtzite structure [(002) peak shift < 0.1°] and strong ferroelectricity (90% remanent polarization at −150 °C). With the decrease in temperature, the coercive field of Al0.75Sc0.25N films increases by over 2 MV/cm, while the remanent polarization only decreases slightly. Rayleigh fitting indicates that the reduction in mobile domain wall density and/or mobility as temperature drops is the main reason for the change of the remanent polarization and coercive field. Moreover, the leakage current decreases with decreasing temperature, accompanied by the transition from the coexistence of Schottky emission and hopping conduction to Schottky emission dominance below −100 °C. The excellent ferroelectricity of the film after being placed at −180 °C for 12 h confirms the robust low-temperature stability. These results fill the gap in understanding the low-temperature performance of Al1−xScxN films, which provide important insights into the fundamental physics and lay the foundation for high-performance, low-loss applications of nitride ferroelectric materials under liquid nitrogen conditions.