Development of molecular design and fabrication technology for a new bio-compatible piezo-electric Perovskite crystal micro-actuator of Bio-MEMS medical device

本研究采用先进的技术手段，设计和制造了一种新型的生物相容压电材料，用于Bio-MEMS医疗器械的生物微致动器。主要研究内容有两个：(1)利用从头算分子力学方法设计了一种新的三元钙钛矿晶体结构。(2)利用螺旋波等离子体溅射装置制备了生物相容压电材料薄膜。1.三元生物相容性压电材料从头算分子设计的研究进展：一种新型钙钛矿型弹性压电材料具有较高的动态响应和发电性能。该材料的设计如下：(1)利用HSAB规则进行生物相容性元件的筛选，HSAB规则是一种评价DNA的重要组成部分鸟氨酸和构成蛋白质的氨基酸相互作用性质的技术。(2)几何…利用基于容差因子法的相互作用评价技术，对钙钛矿型晶体结构的3个候选原子进行了更深入的搜索和选择。(3)用基于密度泛函分析的从头算方法确定了候选晶体材料MgSiO_3的稳定性并评价了其压电性能。用密度泛函分析和电子密度分布方法计算了立方和四方钙钛矿结构的势能，进而探讨了从立方结构到四方结构的自发极化状态的可能性。实验结果表明，在四方自发极化状态下，候选材料MgSiO_3最稳定，表现出良好的压电性。2.利用螺旋波溅射技术制备生物相容的压电材料MgSiO_3。溅射条件的影响因素很多。为了克服这一困难，寻找制造工艺的最佳条件，提出了一种混合方案，该方案结合了基于经验的启发式方法和基于统计分析的实验设计方法。首先，由于所设计的HWPS装置具有很高的真空度和温度性能，并且没有杂质混合，因此我们采用了气压、射频功率和高温溅射的方法来制备具有目标晶体结构的薄膜，并选择了(1)Ar：O_2(流量比)、(2)硅的面积分数、(3)衬底温度和(4)溅射室中的压力四个条件进行了实验设计，以找到最佳的制备条件。我们采用了三个目标函数，即用ESCA测量所制备的薄膜材料的体积分数，用X射线衍射仪测量钙钛矿晶体结构，用悬臂式测试仪评价其压电性能。通过27次试验，利用相互作用图“正交图”找到了最佳的制备条件。制备镁硅薄膜的最佳工艺条件为：(1)Ar：O_2=3：1(0.6sccm：0.2sccm)，(2)硅的面积分数=0.75，(3)衬底温度=700℃，(4)压力=8.0×10~(-2)×10~(-2)×10~(-2)pA。较少

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 … More 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