School of Integrated Circuits, Peking University, Beijing 100871, China.
State Key Laboratory for Turbulence and Complex Systems, Department of Mechanics and Engineering Science, College of Engineering, Peking University, Beijing 100871, China.
Nanoscale. 2023 Apr 13;15(15):7014-7022. doi: 10.1039/d2nr06582g.
The wake-up and fatigue effects exhibited by ferroelectric hafnium oxide (HfO) 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 HfO 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 HfZrO. 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.
铁电氧化铪（HfO）在电循环过程中表现出的苏醒和疲劳效应是限制其发展和应用的两个最主要障碍。尽管有一种主流理论将这些现象与氧空位的迁移和内置场的演化联系起来，但迄今为止，还没有从纳米尺度的角度得到实验观测的支持。通过结合微分相衬扫描透射电子显微镜（DPC-STEM）和能量色散光谱（EDS）分析，我们首次直接观察到铁电 HfO 中氧空位的迁移和内置场的演化。这些确凿的结果表明，苏醒效应是由氧空位分布的均匀化和垂直内置场的减弱引起的，而疲劳效应则与电荷注入和横向局部电场增强有关。此外，我们通过采用低幅度的电循环方案，将场诱导的相变排除在 HfZrO 中苏醒和疲劳的根本原因之外。这项工作通过直接的实验证据阐明了苏醒和疲劳效应的核心机制，这对于优化铁电存储器器件具有重要意义。
