Development of stress-optimised shape memory microvalves

A shape memory microdevice consisting of stress-optimised beams of 100 mu m thickness has been developed to actuate a membrane microvalve for high pressure applications. The lateral widths of the microbeams are designed for homogeneous stress distributions along the beam surfaces allowing an optimised use of the shape memory effect and a minimisation of fatigue effects. Infrared microscopy investigations of the beams reveal maximum temperature variations of 14 K. For valve actuation, a rhombohedral phase transformation is used. This allows operation below pressure differences of 1200 hPa in designs with one valve chamber and below 4500 hPa in pressure-compensated designs with a second valve chamber above the membrane. Maximum gas flows of 1600 seem and work outputs of 35 mu N m are achieved for a driving power of 210 mW. The response times for closing the valves vary between 0.5 and 1.2 a and for opening between 1 and 2 s depending on the applied pressure difference. (C) 1999 Elsevier Science S.A. All rights reserved.