Intrinsic ferroelectricity in Y-doped HfO2 thin films

• Published in: Nature materials 2022-08, Vol.21 (8), p.903-909
• Main Authors: Yun, Yu, Buragohain, Pratyush, Li, Ming, Ahmadi, Zahra, Zhang, Yizhi, Li, Xin, Wang, Haohan, Li, Jing, Lu, Ping, Tao, Lingling, Wang, Haiyan, Shield, Jeffrey E., Tsymbal, Evgeny Y., Gruverman, Alexei, Xu, Xiaoshan
• Format: Article
• Language: English
• Subjects: 639/301/1005/1007; 639/301/119/996; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Crystal defects; Crystal growth; Crystal structure; Crystallinity; Density functional theory; Electronic devices; Ferroelectric materials; Ferroelectricity; Ferroelectrics and multiferroics; Grain size; Hafnium; Hafnium oxide; Linear polarization; MATERIALS SCIENCE; Nanotechnology; Optical and Electronic Materials; Orthorhombic phase; Particle size; Polarization; Room temperature; Silicon; Thin films
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-022-01282-6

Ferroelectric HfO 2 -based materials hold great potential for the widespread integration of ferroelectricity into modern electronics due to their compatibility with existing Si technology. Earlier work indicated that a nanometre grain size was crucial for the stabilization of the ferroelectric phase. This constraint, associated with a high density of structural defects, obscures an insight into the intrinsic ferroelectricity of HfO 2 -based materials. Here we demonstrate that stable and enhanced polarization can be achieved in epitaxial HfO 2 films with a high degree of structural order (crystallinity). An out-of-plane polarization value of 50 μC cm –2 has been observed at room temperature in Y-doped HfO 2 (111) epitaxial thin films, with an estimated full value of intrinsic polarization of 64 μC cm –2 , which is in close agreement with density functional theory calculations. The crystal structure of films reveals the Pca 2 1 orthorhombic phase with small rhombohedral distortion, underlining the role of the structural constraint in stabilizing the ferroelectric phase. Our results suggest that it could be possible to exploit the intrinsic ferroelectricity of HfO 2 -based materials, optimizing their performance in device applications. Hafnium dioxide is of technological interest as it is compatible with silicon; however, previous work indicates that a nanometre grain size is required to generate ferroelectricity. Here ferroelectric Y-doped HfO 2 thin films with high crystallinity are grown with large crystal grain sizes, indicating that ferroelectricity is intrinsic.