First direct observation of the built-in electric field and oxygen vacancy migration in ferroelectric Hf0.5Zr0.5O2 film during electrical cycling

Liang Chen; Zhongxin Liang; Shixuan Shao; Qianqian Huang; Kechao Tang; Ru Huang

doi:10.1039/d2nr06582g

First direct observation of the built-in electric field and oxygen vacancy migration in ferroelectric Hf_0.5Zr_0.5O₂ film during electrical cycling

Nanoscale. 2023 Apr 13;15(15):7014-7022. doi: 10.1039/d2nr06582g.

Authors

Liang Chen¹, Zhongxin Liang¹, Shixuan Shao², Qianqian Huang^{1

3}, Kechao Tang^{1

3}, Ru Huang^{1

3}

Affiliations

¹ School of Integrated Circuits, Peking University, Beijing 100871, China. tkch@pku.edu.cn.
² State Key Laboratory for Turbulence and Complex Systems, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China.
³ Beijing Advanced Innovation Center for Integrated Circuits, Beijing 100871, China.

PMID: 36970751
DOI: 10.1039/d2nr06582g

Abstract

The wake-up and fatigue effects exhibited by ferroelectric hafnium oxide (HfO₂) during electrical cycling are two of the most significant obstacles limiting its development and application. Despite a mainstream theory relating these phenomena to the migration of oxygen vacancies and the evolution of the built-in field, no supportive experimental observations from a nanoscale perspective have been reported so far. By combining differential phase contrast scanning transmission electron microscopy (DPC-STEM) and energy dispersive spectroscopy (EDS) analysis, we directly observe the migration of oxygen vacancies and the evolution of the built-in field in ferroelectric HfO₂ for the first time. These solid results indicate that the wake-up effect is caused by the homogenization of oxygen vacancy distribution and weakening of the vertical built-in field whereas the fatigue effect is related to charge injection and transverse local electric field enhancement. In addition, using a low-amplitude electrical cycling scheme, we exclude field-induced phase transition from the root cause of the wake-up and fatigue in Hf_0.5Zr_0.5O₂. With direct experimental evidence, this work clarifies the core mechanism of the wake-up and fatigue effects, which is important for the optimization of ferroelectric memory devices.