In-Grain Ferroelectric Switching in Sub-5 nm Thin Al_0.74 Sc_0.26 N Films at 1 V

Analog switching in ferroelectric devices promises neuromorphic computing with the highest energy efficiency if limited device scalability can be overcome. To contribute to a solution, one reports on the ferroelectric switching characteristics of sub-5 nm thin Al_0.74 Sc_0.26 N films grown on Pt/Ti/SiO₂ /Si and epitaxial Pt/GaN/sapphire templates by sputter-deposition. In this context, the study focuses on the following major achievements compared to previously available wurtzite-type ferroelectrics: 1) Record low switching voltages down to 1 V are achieved, which is in a range that can be supplied by standard on-chip voltage sources. 2) Compared to the previously investigated deposition of ultrathin Al_1-x Sc_x N films on epitaxial templates, a significantly larger coercive field (E_c ) to breakdown field ratio is observed for Al_0.74 Sc_0.26 N films grown on silicon substrates, the technologically most relevant substrate-type. 3) The formation of true ferroelectric domains in wurtzite-type materials is for the first time demonstrated on the atomic scale by scanning transmission electron microscopy (STEM) investigations of a sub-5 nm thin partially switched film. The direct observation of inversion domain boundaries (IDB) within single nm-sized grains supports the theory of a gradual domain-wall driven switching process in wurtzite-type ferroelectrics. Ultimately, this should enable the analog switching necessary for mimicking neuromorphic concepts also in highly scaled devices.