Epitaxial Ferroelectric Hf0.5 Zr0.5 O2 with Metallic Pyrochlore Oxide Electrodes

Zimeng Zhang; Shang-Lin Hsu; Vladimir A Stoica; Hanjong Paik; Eric Parsonnet; Alexander Qualls; Jianjun Wang; Liang Xie; Mukesh Kumari; Sujit Das; Zhinan Leng; Martin McBriarty; Roger Proksch; Alexei Gruverman; Darrell G Schlom; Long-Qing Chen; Sayeef Salahuddin; Lane W Martin; Ramamoorthy Ramesh

doi:10.1002/adma.202006089

Epitaxial Ferroelectric Hf_0.5 Zr_0.5 O₂ with Metallic Pyrochlore Oxide Electrodes

Adv Mater. 2021 Mar;33(10):e2006089. doi: 10.1002/adma.202006089. Epub 2021 Feb 2.

Authors

Zimeng Zhang¹, Shang-Lin Hsu^{2

3}, Vladimir A Stoica⁴, Hanjong Paik^{5

6}, Eric Parsonnet⁷, Alexander Qualls⁷, Jianjun Wang⁸, Liang Xie¹, Mukesh Kumari¹, Sujit Das¹, Zhinan Leng¹, Martin McBriarty⁹, Roger Proksch¹⁰, Alexei Gruverman¹¹, Darrell G Schlom^{5

6

12}, Long-Qing Chen⁸, Sayeef Salahuddin³, Lane W Martin^{1

13}, Ramamoorthy Ramesh^{1

3

7}

Affiliations

¹ Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA.
² National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
³ Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, 94720, USA.
⁴ Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA.
⁵ Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), Cornell University, Ithaca, NY, 14853, USA.
⁶ Department of Materials Science and Engineering, Cornell University, Ithaca, NY, 14853, USA.
⁷ Department of Physics, University of California, Berkeley, CA, 94720, USA.
⁸ Department of Materials Science and Engineering, Penn State University, University Park, Pennsylvania, 16802, USA.
⁹ EMD Performance Materials, San Jose, CA, 95134, USA.
¹⁰ Asylum Research, Goleta, CA, 93117, USA.
¹¹ Department of Physics, University of Nebraska, Lincoln, NE, 68588-0299, USA.
¹² Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, 14853, USA.
¹³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.

PMID: 33533113
DOI: 10.1002/adma.202006089

Abstract

The synthesis of fully epitaxial ferroelectric Hf_0.5 Zr_0.5 O₂ (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 Pb₂ Ir₂ O₇ (PIO) and Bi₂ Ru₂ O₇ (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.

Keywords: epitaxial growth; ferroelectrics; hafnia.

Abstract

Grants and funding