Coercive Field Reduction in Ultra-thin Al1-XScXN via Interfacial Engineering with a Scandium Electrode

Abstract: Aluminum scandium nitride (AlScN) ferroelectrics are promising for next-generation non-volatile memory applications due to their high remnant polarization as well as fast switching and scalability to nanometer thicknesses. As device dimensions shrink, the coercive field in ultra-thin ferroelectric films increases, which challenges low-voltage operation. We demonstrate that interfacial engineering through bottom electrode selection and strain management reduces this coercive field increase and improves ferroelectric performance. Robust ferroelectricity is observed in ultra-thin AlScN capacitors deposited on a Sc bottom electrode under both alternating current and direct current conditions. The coercive field is reduced by over 20 percent compared to capacitors with an Al bottom electrode. Furthermore, dynamic switching behavior is analyzed using the KAI model. At low frequencies (less than 16.7 kHz), capacitors with Sc and Al bottom electrodes exhibit comparable KAI exponents (0.036 and 0.028, respectively), indicating similar switching kinetics. However, at higher frequencies, the capacitor with an Al bottom electrode shows a significantly higher exponent (0.093), indicating stronger frequency dependence, whereas the capacitor with a Sc bottom electrode maintains a stable exponent of 0.036. Scanning Electron Nanobeam Diffraction is used to measure strain differences in AlScN thin films grown on templates with different lattice mismatch, revealing a correlation between lattice mismatch, film strain, and switching behavior in ultra-thin films.