Study on the Change in the Switching Properties of Ferroelectrics Thin Films with the Passage of Time

铁电薄膜开关特性随时间变化的研究

• 批准号: 18560024
• 负责人: OKAMURA Soichiro
• 金额: $ 2.28万
• 依托单位: Tokyo University of Science
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2006
• 资助国家: 日本
• 起止时间: 2006 至 2007
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18560024/
• 关键词: ferroelectrics; thin film; imprint; hysteresis; built-in field; voltage shift; 強誘電体薄膜; 不揮発性メモリー; 電荷注入; ferroelectrics; thin film; imprint; hysteresis; built-in field; voltage shift; 強誘電体薄膜; 不揮発性メモリー; 電荷注入

Ferroelectric materials have reversible spontaneous polarization and show D -E hysteresis loops. Ideally, the hysteresis loops should be located in the center of a D -E plane. However, actual ferroelectric thin-film capacitors frequently exhibit some shift of the hysteresis loops along electric field axis, that is, "voltage shift." The voltage shift which gradually progresses with time when polarization is aligned is called as "(static or thermal) imprint." This static imprint is one of most serious issues for improving the reliability of ferroelectric random access memories (FeRAMs) because the static imprint progresses in keeping data, and remarkable voltage shifts lead to the change in stored date and the prevention of further polarization reversal.We have carefully investigated the imprint behavior of Pb (Zr,Ti)O_3 (PZT) thin-f-film capacitors. The PZT films were formed on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) with sintering at 700℃, and a post-annealing was carried out at the same temperature after the deposition of top Pt electrodes by rf-magnetron sputtering. The imprint progresses of the PZT thin-film capacitors could be fitted by three equations with the same form which was proposed by Tagantsev et.al., but three different sets of parameters. This indicates that the conduction mechanisms of space charges which caused imprint changed by three steps with time progress. The first mechanism had less temperature dependence while the second one had remarkable temperature dependence. Whether the third one had temperature dependence or not was not clear because of data points were too few, it impacted a longtime imprint. From these results, we speculated that the imprint progresses were controlled by charge injection from electrodes due to first Fowler-Nordheim and second Schottky-emission in interfacial layers, and finally Poole-Frenkel conduction in film bodies.

铁电材料具有可逆赞助的极化，并显示D -E磁滞回路。理想情况下，磁滞回路应位于D -E平面的中心。但是，实际的铁电薄膜电容器经常暴露于沿电场轴的磁滞回路的某种变化，即“电压偏移”。随着极化对齐时的时间逐渐进展的电压偏移称为“（静态或热）烙印”。这种静态烙印是提高铁电随机访问记忆（FERAMS）可靠性的最严重问题之一，因为静态烙印在保留数据方面进展了，并且显着的电压转移导致存储日期的变化和预防进一步的极化反转。我们已经仔细地研究了PB（ZR，TI，TI）O_3（pB ZR）thin（pb ZR）thin（pb）thin（pb）。 PZT膜是通过化学溶液沉积（CSD）在PT/Ti/SiO2/Si底物上形成的，在700℃下烧结，并通过RF-MAGNERTRON溅射在顶部PT电极沉积后，在同一温度下进行了禁令。 PZT薄膜电容器的烙印可以由Tagantsev等人提出的三个方程式拟合，但三个不同的参数集。这表明导致IMpprint的空间电荷的传导机制随时间进展而变化了三个步骤。第一个机制的温度依赖性较小，而第二种机制具有显着的温度依赖性。是否因为数据点太少而没有明确温度依赖性，这影响了长期的烙印。从这些结果中，我们推测，由于第一次福勒 - 诺德海姆（Fowler-Nordheim）和界面层中的第二次肖特基发射，由电子的电荷注入受到电荷注入的控制，最后是膜体中的Poole-frenkel传导。