Unveiling the Origin of Robust Ferroelectricity in Sub-2 nm Hafnium Zirconium Oxide Films.
HfO2-based ferroelectrics are highly expected to lead the new paradigm of nanoelectronic devices owing to their unexpected ability to enhance ferroelectricity in the ultimate thickness scaling limit (≤2 nm). However, an understanding of its physical origin remains uncertain because its direct microstructural and chemical characterization in such a thickness regime is extremely challenging. Herein, we solve the mystery for the continuous retention of high ferroelectricity in an ultrathin hafnium zirconium oxide (HZO) film (∼2 nm) by unveiling the evolution of microstructures and crystallographic orientations using a combination of state-of-the-art structural analysis techniques beyond analytical limits and theoretical approaches. We demonstrate that the enhancement of ferroelectricity in ultrathin HZO films originates from textured grains with a preferred orientation along an unusual out-of-plane direction of (112). In principle, (112)-oriented grains can exhibit 62% greater net polarization than the randomly oriented grains observed in thicker samples (>4 nm). Our first-principles calculations prove that the hydroxyl adsorption during the deposition process can significantly reduce the surface energy of (112)-oriented films, thereby stabilizing the high-index facet of (112). This work provides new insights into the ultimate scaling of HfO2-based ferroelectrics, which may facilitate the design of future extremely small-scale logic and memory devices.
['Lee|Hyangsook|H|', 'Choe|Duk-Hyun|DH|', 'Jo|Sanghyun|S|', 'Kim|Jung-Hwa|JH|', 'Lee|Hyun Hwi|HH|', 'Shin|Hyun-Joon|HJ|', 'Park|Yeehyun|Y|', 'Kang|Seunghun|S|', 'Cho|Yeonchoo|Y|', 'Park|Seontae|S|', 'Moon|Taehwan|T|', 'Eom|Deokjoon|D|', 'Leem|Mirine|M|', 'Kim|Yunseok|Y|https://orcid.org/0000-0003-1794-1248', 'Heo|Jinseong|J|', 'Lee|Eunha|E|', 'Kim|Hyoungsub|H|https://orcid.org/0000-0003-3549-4250']
ferroelectric microstructure Hf0.5Zr0.5O2 orthorhombic ultrathin film