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

基本信息

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

项目摘要

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.

铁电材料具有可逆自发极化，并表现出 D-E 磁滞回线，理想情况下，磁滞回线应位于 D-E 平面的中心，但是，实际的铁电薄膜电容器经常表现出磁滞回线沿电方向的一些偏移。场轴，即“电压偏移”。当极化对齐时，随时间逐渐发生的电压偏移称为“（静态或热）印记”。是提高铁电随机存取存储器（FeRAM）可靠性的最严重的问题之一，因为静态压印在保存数据方面进展，显着的电压变化导致存储数据的变化并防止进一步的极化反转。我们仔细研究了采用化学溶液沉积法在 Pt/Ti/SiO2/Si 衬底上形成 Pb (Zr,Ti)O_3 (PZT) 薄膜电容器的压印行为。 (CSD)，在700℃下烧结，并在射频磁控溅射沉积顶部Pt电极后在相同温度下进行后退火，PZT薄膜电容器的压印进度可以通过三个方程来拟合。与Tagantsev等人提出的形式相同，但参数组不同，这表明引起印记的空间电荷的传导机制随时间发生了三步变化。第一种机制具有较小的温度依赖性，而第二种机制具有显着的温度依赖性，由于数据点太少，我们还不清楚它是否影响了长期印记。由于界面层中的第一次福勒-诺德海姆发射和第二次肖特基发射，以及最后在膜体中的普尔-弗兰克尔传导，压印过程受到来自电极的电荷注入的控制。