Coercive Field Reduction in Ultra-Thin Al1-xScxN via Interfacial Engineering with a Scandium Bottom Electrode

Aluminum scandium nitride (AlScN) ferroelectrics are promising for next-generation non-volatile memory applications due to their high remnant polarization when compared to Pb(ZrxTi1-x)O3 and doped-HfO2 material systems, as well as their fast switching and scalability to nanometer thicknesses. For AlScN films at a 10 nm thickness, their coercive field substantially increases, which hinders low voltage operation. We demonstrate that interfacial engineering through bottom electrode selection and strain management reduces this coercive field increase with scaling and improves ferroelectric performance. We report robust ferroelectricity 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% compared to capacitors with an Al bottom electrode. We evaluated the difference in dynamic switching behavior across a decade of frequency by applying the frequency-scaling power law. At frequencies <16.7 kHz, the capacitors with Sc and Al bottom electrodes exhibit comparable frequency-scaling exponents of 0.030 and 0.028, respectively, indicating similar switching kinetics. However, at higher frequencies, the capacitor with an Al bottom electrode shows a significantly higher exponent value of 0.063, indicating a stronger frequency dependence, whereas the capacitor with a Sc bottom electrode maintains a stable exponent of 0.030, suggesting a lower frequency dependence during faster switching scenarios. We employed scanning electron nanobeam diffraction to measure the strain difference in AlScN thin films grown on templates with different lattice mismatches, providing a correlation between lattice mismatch, film strain, and switching behavior in ultra-thin film systems.