Development of magnetic field driven microactuators made by ferromagnetic shape memory alloy thin films

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Fe-Pd ferromagnetic alloy containing about 30at% Pd shows fcc-fct martensitic transformation which is induced by change in temperature and/or magnetic field. This means that this Fe-Pd alloy has a possibility to show a magnetic field induced shape memory effect. The development of the material showing magnetic field induced shape memory effect allows us to fabricate a robust actuator with faster response than Ti-Ni shape memory alloy. When we consider Fe-Pd alloy to use as a microactuator in future, a fabrication process of this alloy in thin film form must be established. The primary purpose of this work was to establish the fabrication process of this material in thin film form and the goal was to fabricate the Fe-Pd alloy microactuator using Si-MEMS technique.First of all, we have decided the optimal conditions to deposit Fe-Pd films under precise compositional control using dual source dc magnetron sputtering. The films containing 28〜32at% Pd after annealing at 900℃ showed fcc-fct … More martensitic transformation accompanied by shape memory effect. The shape memory behavior of annealed films was characterized quantitatively using thermal cycling tests under various constant loads. The Fe-Pd films containing less than 30at% Pd showed shape memory effect at above room temperature. However, when the temperature was lower than -80℃, they showed irreversible strain originated from fct-bct transformation. This behavior suggests there is the limitation in temperature for use of this alloy system. The fct martensite of Fe-Pd alloy containing more than 30at% Pd was found to be stable though the fcc-fct transformation temperature is lower than room temperature. The transformation temperature rises with increasing applied stress along with Clasius-Clapayron relationship. It is confirmed that the Fe-Pd films containing more than 30at% Pd can be used at above room temperature when a suitable bias load is applied. We have also succeeded to fabricate the cantilever type microactuator which is actually driven by Joule heat. These results have already reported in international journals. Less