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Ultrathin AlScN for low-voltage driven ferroelectric-based devices

Thickness scaling of ferroelectricity in AlScN is a determining factor for its potential application in neuromorphic computing and memory devices. In this letter, we report on ultrathin (10 nm) Al0.72Sc0.28N films that are ferroelectrically switchable at room temperature. All-epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering onto GaN/sapphire substrates followed by an in situ Pt capping approach to avoid oxidation of the Al0.72Sc0.28N film surface. Structural characterization by X-ray diffraction and transmission electron microscopy reveals the established epitaxy. The thus obtained high-quality interfaces in combination with the in situ capping is expected to facilitate ferroelectric switching of AlScN in the ultrathin regime. The analysis of the relative permittivity and coercive field dependence on the Al0.72Sc0.28N film thicknesses in the range of 100 nm down to 10 nm indicates only moderate scaling effects, suggesting that the critical thickness for ferroelectricity is not yet approached. Furthermore, the deposited layer stack demonstrates the possibility of including ultrathin ferroelectric AlScN into all-epitaxial GaN-based devices using sputter deposition techniques. Thus, our work highlights the integration and scaling potential of all-epitaxial ultrathin AlScN offering high storage density paired with low voltage operation desired for state of the art ferroelectric memory devices.