Ultrathin Al1−xScxN for Low-Voltage-Driven Ferroelectric-Based Devices

Abstract

Thickness scaling of ferroelectricity in Al1−xScxN is a determining factor for its potential application in neuromorphic computing and memory devices. In this letter, ultrathin (10 nm) Al0.72Sc0.28N films that are ferroelectrically switchable at room temperature are reported on. 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 films in combination with in situ capping facilitate ferroelectric switching of Al1−xScxN in the ultrathin regime. The analysis of the relative permittivity and coercive field dependence on Al0.72Sc0.28N film thicknesses in the range from 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 Al1−xScxN into all-epitaxial GaN-based devices using sputter deposition techniques. Thus, the integration and scaling potential of all-epitaxial ultrathin Al1−xScxN offering high storage density paired with low-voltage operation desired for state-of-the-art ferroelectric memory devices are highlighted.