| Co-Investigator(Kenkyū-buntansha) |
SHIBUTANI Yoji Osaka Univ., Eng., Professor, 大学院・工学研究科, 教授 (70206150)
UEDA Sei OSAKA INSTITUTE OF TECHNOLOGY, Eng., Professor, 工学部, 教授 (10176589)
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| Research Abstract |
In this research, a advanced technology development was performed to design and fabricate a new bio-compatible piezo-electric material for a bio-microactuator of Bio-MEMS medical device. There were two main research subjects ; (1)A new three elements Perovskite crystal structure was designed by using ab-initio molecular mechanics analysis. (2)A thin film of bio-cornpatible piezo-electric material was fabricated by using Helicon wave plasma sputtering apparatus. A summery is shown as below.
1.Develonment of ab-initio molecular design of three elements bio-comnatible piezo-electric material.
A new Perovskite crystal type elastic piezo-electric material shows a high performance of dynamic response and power generation. This material was designed as follow : (1)Selection of bio-compatible 'element was carried out by using HSAB rule, which is the Technique of evaluating interaction properties with Guanine, which is one of important DNA, and Amino acid, which constitutes protein. (2)A geometri
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cal search and selection of three candidate atoms of Perovskite type crystal structure was carried out by using the interaction evaluation technique based on the tolerance factor method. (3)Ab-initio molecular structure analysis based on the density function analysis was used to confirm the stability and evaluate piezo-electric properties of a candidate crystal material MgSiO_3. The density function analysis and the electron density distribution method evaluate potential energies of a cubic crystal structure and a tetragonal Perovskite one, and further a possibility of spontaneous polarization state from cube structure to tetragonal one is investigated. It is confirmed that the candidate material MgSiO_3 becomes the most stable in the state of tetragonal spontaneous polarization, and it is concluded that MgSiO_3 shows a high-performance of piezoelectric characteristics.
2.Fabrication technology development of a bio-compatible piezo-electric material MgSiO_3 by using Helicon wave sputtering apparatus.
Helicon wave plasma sputtering (HWPS) apparatus was purchased by this research grant and used to fabricate thin film of MgSiO_3 Perovskite crystal type piezo-electric material. Many factors of sputtering conditions can be considered. To overcome this difficulty to find an optimum condition for a fabrication technology, a hybrid scheme was introduced, which is combined with the heuristic method based on the experience and the experimental design method based on a statistical analysis. At first, this designed HWPS apparatus shows a high performance of vacuum and temperature without a contaminant mixing, therefore we adopted 10^<-4>Pa pressure, RF electric power and a high temperature sputtering to fabricate a thin film with a aimed crystal structure "as deposited."
Four conditions, such as, (1)Ar:O_2 (flux ratio), (2)area fraction of Si, (3)substrate temperature and (4)pressure in the chamber of sputtering, were selected to carry out the experimental design method to find an optimum fabrication condition. We have employed three objective functions, such as the volume fraction of fabricated thin film material measured by ESCA, the Perovskite crystal structural evaluation measured by XRD analyses, and the piezo-electric property, d_<31>, evaluated by a cantilever type testing apparatus. A optimum fabrication condition was found by using interaction diagram, "the orthogonal diagram," through twenty seven trials. The best condition to fabricate a thin piezoelectric film of MgSiO_3. is indicated as follo9w ; (1)Ar:O_2=3:1 (0.6sccm:0.2sccm), (2)area fraction of Si=0.75, (3)Substrate temperature=700℃ and (4)Pressure=8.0x10^<-2>Pa. Less
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