Development of MgSiO3 biocompatible piezoelectric film for Bio-MEMS actuator

In this study, a sputtering technique for a Bio-MEMS thin film piezoelectric actuator is developed, by employing a newly designed biocompatible piezoelectric material M-SiO3 that has a tetragonal perovskite lattice crystal structure. This crystal structure was designed by using numerical analyses, such as the HSAB rule, the geometrical compatibility assessment and the first principle based DFT calculation. In general, MoSiO3 has an orthorhombic perovskite structure in the nature. Therefore, we try to generate a tetragonal structure by employing 1) the helicon wave plasma sputtering (HWPS) method, which can produce large energy atoms under a low working pressure and easy to control the lattice constant for growing the tetragonal structure of MoSiO3, and 2) a bio-compatible substrate Ir/Ti/Si, to produce a thin film of MgSiO3 tetragonal perovskite. Ir/Ti/Si substrate has better compatibility with MgSiO3 (111) plane, because of its close lattice constant. An optimal condition of HWPS to generate MgSiO3 tetragonal perovskite structure was sought by using the experimental design method and the response surface method. We found that 1) the substrate temperature and 2) the target composition ratio are significant influent factors for MgSiO3 film generation. In this searching process, we evaluated the properties of MgSiO3 films by 1) the surface roughness measured by AFM, and 2) the chemical compositions measured by XPS, and 3) the crystal structure by XRD. Finally, MgSiO3 thin film was successfully fabricated and the piezoelectric and ferroelectrics properties were measured.