Stress-optimised shape memory microvalves

A gas valve of 6/spl times/6/spl times/2 mm/sup 3/ size has been developed for high force applications. Stress-optimised shape memory microbeams of 100 /spl mu/m thickness are used to control the deflection of a membrane above a valve chamber with a valve seat of 0.5 mm inner diameter. For stress-optimisation, the lateral widths of the beams 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. For actuation, a rhombohedral phase transformation is used. This allows operation below differential pressures of 1200 hPa in designs with one valve chamber. At 1200 hPa, a gas flow of 1600 sccm and a work output of 35 /spl mu/Nm are achieved for a driving power below 450 mW. Designs with a second valve chamber above the membrane allow compensation of pressure on the membrane and thus operation at differential pressures up to 4500 hPa. The response times for closing the valves vary between 0.5 and 1.2 s and for opening between 1 and 2 s depending on the applied pressure.