2005 Fiscal Year Final Research Report Summary
Interface Control of Bismuth-Layer-Structured Ferroelectric Thin Film Using TiO2 Anatase-Buffer Layer
| Project/Area Number |
16560024
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Thin film/Surface and interfacial physical properties
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| Research Institution | Faculty of Science, TOKYO UNIVERSITY OF SCIENCE |
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Principal Investigator |
TSUKAMOTO Takeyo Tokyo University of Science, Faculty of Science, 理学部, 教授 (30084312)
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| Co-Investigator(Kenkyū-buntansha) |
HIGUCHI Tohru Tokyo University of Science, Faculty of Science, 理学部, 助手 (80328559)
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| Project Period (FY) |
2004 – 2005
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| Keywords | Ferroelectric thin film / Bismuth-Layer-Structured Ferroelectric / MOCVD / TiO_2 Anatase / Buffer Layer / Interface Control / Bi4Ti3O12 / Remanent Polarization |
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| Research Abstract |
Bismuth layer-structured ferroelectric Bi_4Ti_3O_<12> (BIT) has been expected to be applied to nonvolatile ferroelectric random access memories (FeRAMs) with nondestructive readout operation, because of its low dielectric constant and coercive field. The BIT thin films are useful lead-free and fatigue-free ferroelectric materials that exhibit superior ferroelectricity even when using Pt electrodes. The BIT exhibits coercive fields (E_c) of 3.5 kV/cm and 50 kV/cm, and remanent polarization (P_r) of 4.0 μC/cm^2 and 50 μC/cm^2 along the c- and a-axes, respectively. In this work, a- and b-axis-oriented BIT thin films were prepared on (111)-oriented Pt/Ti/SiO_2/Si substrates by metalorganic chemical vapor deposition (MOCVD) using Bi(CH_3)_3 and Ti(i-OCH_3H_7)_4 sources. In order to achieve the a- and b-axis orientations of BIT thin film, we inserted a TiO2 anatase buffer layer between the BIT thin film and Pt/Ti/SiO_2/Si substrate. TiO_2 anatase buffer layers were prepared on (111) Pt/Ti/SiO_2/Si substrates by MOCVD. The BIT thin film with the TiO_2 anatase buffer layer prepared at 500℃ exhibited highly a- and b-axis-oriented BIT single phases, although the BIT thin film with no buffer layer exhibited a c-axis orientation. The interface between the BIT thin film and the substrate was very smooth. The BIT thin film consisted of small grains and exhibited a good P-E hysteresis loop. The ferroelectricity of the BIT thin film with the TiO_2 anatase buffer layer strongly depends on the thickness ratio of the BIT thin film to the TiO_2 anatase layer, indicating that the TiO_2 anatase buffer layer acts not as barrier layer but as an initial nucleation layer of the BIT thin film. When the thickness ratio is fixed at [(BIT)/(TiO_2)]=15, the remanent polarization (P_r) and the coercive field (Ec) were 2P_r=81.6 μC/cm^2 and 2E_c=250 kV/cm, respectively. The dielectric constant (ε_r) was 160.
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