Interface effects in the phase determination of Hf0.5Zr0.5O2 epitaxial thin films

Jesse Schimpf; Wang Zhang; Mahir Manna; Sandhya Susarla; Xue Zeng Lu; James M. Rondinelli; Lane W. Martin

doi:10.1063/5.0243530

Interface effects in the phase determination of Hf_0.5Zr_0.5O₂ epitaxial thin films

Jesse Schimpf, Wang Zhang, Mahir Manna, Sandhya Susarla, Xue Zeng Lu, James M. Rondinelli, Lane W. Martin^*

^*Corresponding author for this work

Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

Abstract

HfO₂-based ferroelectrics show tremendous potential for applications in computing technologies, but questions remain as to what dictates the stabilization of the desired phase. Here, it is demonstrated that the substrate the film is grown on is more influential than factors such as thickness, defect content, and strain. The presence of different possible polymorphs of Hf_0.5Zr_0.5O₂ are observed to vary widely for different substrate materials—with La_0.67Sr_0.33MnO₃, (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7, and Al₂O₃ being (more) optimal for stabilizing the ferroelectric-orthorhombic phase. This substrate effect is found to be more influential than any changes observed from varying the film thickness (7.5-60 nm), deposition environment (oxygen vs argon), and annealing temperature (400-600 °C) in vacuum (10⁻⁵ Torr). X-ray diffraction and scanning transmission electron microscopy verify the phases present, and capacitor-based studies reveal ferroelectric behavior (or lack thereof) consistent with the phases observed. First-principles calculations suggest that forming oxygen vacancies in Hf_0.5Zr_0.5O₂ lowers its work function, driving electrons away and helping to stabilize the ferroelectric phase. Substrates with a high work function (e.g., La_0.67Sr_0.33MnO₃) facilitate this electron transfer but must also have sufficient ion conductivity to support oxygen-vacancy formation in Hf_0.5Zr_0.5O₂. Together, these observations help clarify key factors essential to the stabilization of HfO₂-based ferroelectrics.

Original language	English (US)
Article number	011104
Journal	APL Materials
Volume	13
Issue number	1
DOIs	https://doi.org/10.1063/5.0243530
State	Published - Jan 1 2025

Funding

J.S. acknowledges the support of the National Science Foundation (NSF) under Grant No. DMR-2102895. J.M.R. acknowledges the support of the NSF under Grant No. DMR-2104397. L.W.M acknowledges the support of the NSF under Grant No. DMR-2329111. W.Z. and X.Z.L. were supported by the open research fund of Key Laboratory of Quantum Materials and Devices (Southeast University), Ministry of Education. S.S. and M.M. acknowledge the use of the Eyring Materials Center for imaging. S.S. and M.M. also acknowledge the FSE-ASU startup funds. This research was supported, in part, through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. Part of the calculations were performed on the high-performance computers, supported by the Big Data Computing Center of Southeast University.

ASJC Scopus subject areas

General Materials Science
General Engineering

Access to Document

10.1063/5.0243530

Cite this

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title = "Interface effects in the phase determination of Hf0.5Zr0.5O2 epitaxial thin films",

abstract = "HfO2-based ferroelectrics show tremendous potential for applications in computing technologies, but questions remain as to what dictates the stabilization of the desired phase. Here, it is demonstrated that the substrate the film is grown on is more influential than factors such as thickness, defect content, and strain. The presence of different possible polymorphs of Hf0.5Zr0.5O2 are observed to vary widely for different substrate materials—with La0.67Sr0.33MnO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and Al2O3 being (more) optimal for stabilizing the ferroelectric-orthorhombic phase. This substrate effect is found to be more influential than any changes observed from varying the film thickness (7.5-60 nm), deposition environment (oxygen vs argon), and annealing temperature (400-600 °C) in vacuum (10−5 Torr). X-ray diffraction and scanning transmission electron microscopy verify the phases present, and capacitor-based studies reveal ferroelectric behavior (or lack thereof) consistent with the phases observed. First-principles calculations suggest that forming oxygen vacancies in Hf0.5Zr0.5O2 lowers its work function, driving electrons away and helping to stabilize the ferroelectric phase. Substrates with a high work function (e.g., La0.67Sr0.33MnO3) facilitate this electron transfer but must also have sufficient ion conductivity to support oxygen-vacancy formation in Hf0.5Zr0.5O2. Together, these observations help clarify key factors essential to the stabilization of HfO2-based ferroelectrics.",

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