Abstract
Passive microvalves have been fabricated into a 2.7 mu m thin titanium membrane. The valves consist of a perforated thin membrane of polyimide stretched over an opening in the titanium membrane. The diameters of the openings in the polyimide and titanium membranes are 100 mu m and 180 mu m, respectively. The diameter of the valve is 1 mm. The thickness of the polyimide membrane has been varied between 0.45 and 2.15 mu m. The microvalves are fabricated by sputtering of thin films, photolithography, etching of sacrificial layers, and transfer of the membranes from a substrate to a rigid frame. Tests with helium showed in all cases a leakage of less than 4*10-4 hPa l s-1 through the closed valve. The helium flow through the open microvalves attained 3.2 hPa l s-1 at a pressure difference of 250 hPa corresponding to a mass flow of 2.4 ml s-1 at an absolute pressure of 1250 hPa.