Doped HfO2 thin films exhibit robust ferroelectric properties even for nanometric thicknesses, are compatible with current Si technology, and thus have great potential for the revival of integrated ferroelectrics. Phase control and reliability are core issues for their applications. Here, we show that, in (111)-oriented 5%La:HfO2 (HLO) epitaxial thin films deposited on (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates, the flexoelectric effect, arising from the strain gradient along the film's normal, induces a rhombohedral distortion in the otherwise Pca21 orthorhombic structure. Density functional calculations reveal that the distorted structure is indeed more stable than the pure Pca21 structure, when applying an electric field mimicking the flexoelectric field. This rhombohedral distortion greatly improves the fatigue endurance of HLO thin films by further stabilizing the metastable ferroelectric phase against the transition to the thermodynamically stable non-polar monoclinic phase during repetitive cycling. Our results demonstrate that the flexoelectric effect, though negligibly weak in bulk, is crucial to optimize the structure and properties of doped HfO2 thin films with nanometric thicknesses for integrated ferroelectric applications.
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September 2023
Research Article|
September 11 2023
Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films
Peijie Jiao
;
Peijie Jiao
(Conceptualization, Data curation, Formal analysis, Investigation, Software, Visualization, Writing – original draft)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Hao Cheng
;
Hao Cheng
(Formal analysis, Investigation, Methodology, Software, Visualization, Writing – original draft)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Jiayi Li
;
Jiayi Li
(Data curation, Formal analysis, Software, Visualization, Writing – original draft)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Hongying Chen;
Hongying Chen
(Formal analysis, Software, Visualization, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Zhiyu Liu;
Zhiyu Liu
(Data curation, Formal analysis, Visualization)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Zhongnan Xi
;
Zhongnan Xi
(Formal analysis, Methodology, Visualization, Writing – original draft)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Wenjuan Ding
;
Wenjuan Ding
(Methodology, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Xingyue Ma
;
Xingyue Ma
(Formal analysis)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Jian Wang
;
Jian Wang
(Formal analysis)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Ningchong Zheng;
Ningchong Zheng
(Methodology)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Yuefeng Nie
;
Yuefeng Nie
(Methodology, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Yu Deng
;
Yu Deng
(Conceptualization, Funding acquisition, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Laurent Bellaiche
;
Laurent Bellaiche
(Conceptualization, Writing – review & editing)
2
Physics Department, Institute for Nanoscience and Engineering, University of Arkansas
, Fayetteville, Arkansas 72701, USA
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Yurong Yang
;
Yurong Yang
a)
(Funding acquisition, Visualization, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
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Di Wu
Di Wu
a)
(Conceptualization, Formal analysis, Funding acquisition, Project administration, Supervision, Visualization, Writing – review & editing)
1
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, Jiangsu Key Laboratory of Artificial Functional Materials, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University
, Nanjing 210093, China
3
School of Materials Science and Intelligent Engineering, Nanjing University
, Suzhou 215163, China
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Appl. Phys. Rev. 10, 031417 (2023)
Article history
Received:
February 02 2023
Accepted:
August 22 2023
Citation
Peijie Jiao, Hao Cheng, Jiayi Li, Hongying Chen, Zhiyu Liu, Zhongnan Xi, Wenjuan Ding, Xingyue Ma, Jian Wang, Ningchong Zheng, Yuefeng Nie, Yu Deng, Laurent Bellaiche, Yurong Yang, Di Wu; Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films. Appl. Phys. Rev. 1 September 2023; 10 (3): 031417. https://doi.org/10.1063/5.0144958
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