Epitaxial Ferroelectric Hf 0.5 Zr 0.5 O 2 with Metallic Pyrochlore Oxide Electrodes

• Published in: Advanced materials (Weinheim) Vol. 33; no. 10; p. e2006089
• Main Authors: Zhang, Zimeng, Hsu, Shang-Lin, Stoica, Vladimir A, Paik, Hanjong, Parsonnet, Eric, Qualls, Alexander, Wang, Jianjun, Xie, Liang, Kumari, Mukesh, Das, Sujit, Leng, Zhinan, McBriarty, Martin, Proksch, Roger, Gruverman, Alexei, Schlom, Darrell G, Chen, Long-Qing, Salahuddin, Sayeef, Martin, Lane W, Ramesh, Ramamoorthy
• Format: Journal Article
• Language: English
• Published: Germany Wiley Blackwell (John Wiley & Sons) 01.03.2021
• Subjects: ferroelectrics; epitaxial growth; hafnia
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202006089

The synthesis of fully epitaxial ferroelectric Hf Zr O (HZO) thin films through the use of a conducting pyrochlore oxide electrode that acts as a structural and chemical template is reported. Such pyrochlores, exemplified by Pb Ir O (PIO) and Bi Ru O (BRO), exhibit metallic conductivity with room-temperature resistivity of <1 mΩ cm and are closely lattice matched to yttria-stabilized zirconia substrates as well as the HZO layers grown on top of them. Evidence for epitaxy and domain formation is established with X-ray diffraction and scanning transmission electron microscopy, which show that the c-axis of the HZO film is normal to the substrate surface. The emergence of the non-polar-monoclinic phase from the polar-orthorhombic phase is observed when the HZO film thickness is ≥≈30 nm. Thermodynamic analyses reveal the role of epitaxial strain and surface energy in stabilizing the polar phase as well as its coexistence with the non-polar-monoclinic phase as a function of film thickness.