Titanium-Nickel Shape Memory Thin Film Actuators for Micromachined Valves

Abstract

AbstractMicroelectromechanical valves have been fabricated from silicon wafers using standard bulk micromachining techniques, which utilize thin (2 μm) films of sputter-deposited titaniumnickel as the actuators. The TiNi shape memory alloy actuators are thermally driven by resistive heating, through the passage of an electric current. TiNi diaphragms (8.4 mm wide) are fabricated and tested in a pressure-temperature controlled fixture in order to determine the mechanical properties of the shape memory film. If a silicon island is left attached to the center of the diaphragm, this can act as a “boss” whose movement against an orifice will open and close the valve. The orifice can be etched into a second silicon wafer or machined from another rigid material. Use of mechanical spacers and external bias springs result in a normally-closed or normally-open configuration. Modulations of up to 90 percent have been observed in gas flows of up to 0.6 liter/min. Water flows as high as 5 ml/min. have been modulated by 60 percent.