The fabrication of thin film NiTi shape memory alloy micro actuator for MEMS application

摘要

Thin film SMA (Shape memory alloy) is a useful method for MEMS (Microelectromechanical Systems) actuator. This is because the thin film has an improved frequency response compared to bulk SMA, high work density, and produces large strain. A novel two-way thin film NiTi (Nickel Titanium) shape memory alloy actuator is presented in this paper. Thin film shape memory alloy is sputter-deposited onto a silicon wafer in an ultra high vacuum system. Transformation temperatures of the deposited NiTi film are measured by residual stress measurement at temperatures from 25 °C to 120 °C. Test results show that the M{sub}f (Martensite Finish Temperature) is around 60 °C and A{sub}f (Austenite Finish Temperature) is around 110 °C. A free standing NiTi membrane (10 mm × 10mm and 3 μm thick) is fabricated using MEMS technology. We found that a mixture of HF (Hydro Fluidic Acid), HNO{sub}3 (Nitric Acid) and DI (Deionized) water with thick photo resist mask works best for the fabrication process. The membrane is hot-shaped in different shapes such as dome shape, pyramidal shape, and cylindrical shape. Results indicate that when the temperature of the NiTi film exceeds A{sub}f, the NiTi membrane transforms into the trained hot-shape. When the temperature cools down to room temperature, the membrane returns to the initial flat shape.