Shape memory microvalves based on thin films or rolled sheets

This paper reports on recent developments of gas microvalves, which are actuated by microfabricated shape memory alloy (SMA thin films or sheets with stress-optimised shapes. Ti-Ni, Ti-Ni-Cu and Ti-Ni-Pd thin films of 10 mu m thickness have been fabricated by sputter deposition. Ti-Ni sheets of 30-100 mu m thickness have been made by hot-forging and cold-rolling. The main fabrication technologies of the valves have been laser cutting or electrolytic photoetching and subsequent hybrid integration. By variation of the chemical composition of the thin films, the valve operation temperature was adjusted between 30 and 120 degrees C. The thin film devices have been operated in tension mode allowing the control of maximum pressure differences of 3000 hPa (3 bar). The corresponding maximum gas flow is about 360 Standard ccm. The maximum control power for Ti-Ni-Cu and Ti-Ni microvalves is 110 mW, for Ti-Ni-Pd microvalves 220 mW. SMA sheet microdevices have been operated in bending mode, which allows large strokes and thus large gas flows. (C) 1999 Elsevier Science S.A. All rights reserved.