Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films
Abstract
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 01, 2023
- Source ID
- 10.1063/5.0144958
Entities
People
- Di Wu
- Hao Cheng
- Hongying Chen
- Jian Wang
- Jiayi Li
- Laurent Bellaiche
- Ningchong Zheng
- Peijie Jiao
- Wen-Juan Ding
- Xingyue Ma
- Yu Deng
- Yuefeng Nie
- Yurong Yang
- Zhiyu Liu
- Zhongnan Xi
Organizations
- Nanjing University
- National Natural Science Foundation of China
- Natural Science Foundation of Jiangsu Province
- Office of Naval Research
- University of Arkansas