Proposal of new material for ferroelectric thin film memories and method to evaluate material properties.

提出铁电薄膜存储器新材料和评估材料性能的方法。

• 批准号: 12450266
• 负责人: TSURUMI Takaaki
• 金额: $ 10.69万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450266/
• 关键词: ferroelectric thin film memory; hysteresis curve; sputtering; domain structure; lead titanate; perovskite compounds

The purpose of the present research was 1) to develop a new ferroelectric material which could be crystallized below 450 ℃ and 2) to establish the method to measure the polarization vs. electric-field (P-E) hysteresis curves at high frequencies. These are considerably important to realize the ferroelectric thin film memories (FeRAMs). For the first purpose, we have proposed (Pb,Sr)TiO_3 as a ferroelectric material and thin films of this material were prepared by the sputtering process. The relation between the substrate temperature and the chemical composition of the films was first studied and it was confirmed that the lead component in the films was reduced with increasing substrate temperature. DC-bias field was applied to the substrate during the deposition. Negative field markedly reduced the deposition rate of lead component. By optimizing the deposition conditions, the crystallization temperature of PST was decreased as low as 430 ℃. The addition of Bi improved the remanent polarization up to 20 μC/cm^2. On the other hand, for the second purpose, we have employed a high-speed operation amplifier as a current-voltage converter in the measuring system and the displacive current through the PZT thin film was converted to the voltage signal followed by integrating to calculated polarization. The coercive field (E_c) of the PZT thin films strongly depended on the measuring frequency, nevertheless their remanent polarization was almost independent of it. The domain switching kinetics of PZT thin films could be explained by the nucleation-controlled model. A guideline to make FeRAMs with a high operating speed was proposed.

本研究的目的是：1）开发一种能在450 ℃以下晶化的新型铁电材料; 2）建立一种测量高频下极化-电场（P-E）电滞曲线的方法。这对实现铁电薄膜存储器（FeRAM）具有重要意义。第一，我们提出了（Pb，Sr）TiO_3作为铁电材料，并用溅射法制备了这种材料的薄膜。首先研究了衬底温度与薄膜化学成分之间的关系，证实了随着衬底温度的升高，薄膜中的铅成分减少。在沉积过程中向衬底施加直流偏置场。负电场显著降低了铅组分的沉积速率。通过优化沉积条件，使PST的晶化温度降低到430 ℃。Bi的加入将反射极化提高到20 μC/cm ^2。另一方面，对于第二个目的，我们采用了一个高速运算放大器作为电流-电压转换器的测量系统和通过PZT薄膜的位移电流转换成电压信号，然后积分计算极化。PZT薄膜的矫顽场（Ec）与测量频率有很强的依赖关系，而反射极化几乎与频率无关，PZT薄膜的畴变动力学可用成核控制模型来解释。提出了一种制作高速铁电存储器的指导思想。