Wang Xuepei, Wen Yichen, Wu Maokun, Cui Boyao, Wu Yi-Shan, Li Yuchun, Li Xiaoxi, Ye Sheng, Ren Pengpeng, Ji Zhi-Gang, Lu Hong-Liang, Wang Runsheng, Zhang David Wei, Huang Ru
National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Department of Micro/Nano Electronics, Shanghai Jiao Tong University, Shanghai 200240, China.
State Key Laboratory of ASIC and System, School of Microelectronics, Shanghai Institute of Intelligent Electronics and Systems, Fudan University, Shanghai 200433, China.
ACS Appl Mater Interfaces. 2023 Mar 29;15(12):15657-15667. doi: 10.1021/acsami.2c22263. Epub 2023 Mar 16.
It is commonly believed that the impact of the top electrodes on the ferroelectricity of hafnium-based thin films is due to strain engineering. However, several anomalies have occurred that put existing theories in doubt. This work carries out a detailed study of this issue using both theoretical and experimental approaches. The 10 nm HfZrO (HZO) films are prepared by atomic layer deposition, and three different top capping electrodes (W/MO/ITO) are deposited by physical vapor deposition. The electrical testing finds that the strain does not completely control the ferroelectricity of the devices. The results of further piezoelectric force microscopy characterization exclude the potential interference of the top capping electrodes and interface for electrical testing. In addition, through atomic force microscopy characterization and statistical analysis, a strong correlation between the grain size of the top electrode and the grain size of the HZO film has been found, suggesting that the grain size of the top electrode can induce the formation of the grain size in HZO thin films. Finally, the first-principles calculation is carried out to understand the impact of the strain and grain size on the ferroelectric properties of HZO films. The results show that the strain is the dominant factor for ferroelectricity when the grain size is large (>10 nm). However, when the grain size becomes thinner (<10 nm), the regulation effect of grain sizes increases significantly, which could bring a series of benefits for device scaling, such as device-to-device variations, film uniformity, and domain switch consistency. This work not only completes the understanding of ferroelectricity through top electrode modulation but also provides strong support for the precise regulation of ferroelectricity of nanoscale devices and ultrathin HZO ferroelectric films.
人们普遍认为，顶部电极对铪基薄膜铁电性的影响归因于应变工程。然而，出现了一些异常情况，使现有理论受到质疑。这项工作使用理论和实验方法对该问题进行了详细研究。通过原子层沉积制备了10纳米的HfZrO（HZO）薄膜，并通过物理气相沉积沉积了三种不同的顶部覆盖电极（W/MO/ITO）。电学测试发现，应变并不能完全控制器件的铁电性。进一步的压电力显微镜表征结果排除了顶部覆盖电极和界面在电学测试中的潜在干扰。此外，通过原子力显微镜表征和统计分析，发现顶部电极的晶粒尺寸与HZO薄膜的晶粒尺寸之间存在很强的相关性，这表明顶部电极的晶粒尺寸可以诱导HZO薄膜中晶粒尺寸的形成。最后，进行了第一性原理计算，以了解应变和晶粒尺寸对HZO薄膜铁电性能的影响。结果表明，当晶粒尺寸较大（>10纳米）时，应变是铁电性的主导因素。然而，当晶粒尺寸变细（<10纳米）时，晶粒尺寸的调节作用显著增加，这可能为器件缩放带来一系列好处，如器件间变化、薄膜均匀性和畴切换一致性。这项工作不仅通过顶部电极调制完成了对铁电性的理解，还为纳米级器件和超薄HZO铁电薄膜铁电性的精确调控提供了有力支持。
