2001 Fiscal Year Final Research Report Summary
Proposal of new material for ferroelectric thin film memories and method to evaluate material properties.
| Project/Area Number |
11555233
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
無機工業化学
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
TSURUMI Takaaki Graduate School of Science and Engineering, Department of Material Science, Professor, 大学院・理工学研究科, 教授 (70188647)
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| Co-Investigator(Kenkyū-buntansha) |
YAMASHITA Yahachi Toshiba Corp., R & D center, Chief Researcher, 研究開発センター, 主任研究員
OHASHI Naoki National Institute for Materials Science, Senior Researcher, 主任研究員 (60251617)
WADA Satoshi Graduate School of Science and Engineering, Department of Material Science, Associate Professor, 大学院・理工学研究科, 助教授 (60240545)
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| Project Period (FY) |
1999 – 2001
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| Keywords | ferroelectric thin film memory / hysteresis curve / sputtering / domain structure / lead titanate / perovskite compounds |
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| Research Abstract |
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.
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