Structure and characterization of a planar normally closed bulk-micromachined piezoelectric valve for fuel cell applications

Microfuel cell systems require microvalves that are chemically tolerant of hydrogen, have thermally insensitive activation mechanisms, and tight geometric constraints. A planar bulk-micromachined piezoelectric valve for portable fuel cell system is proposed. The actuating diaphragm and the valve seat are etched on silicon wafers. A piezoelectric bimorph disc is glued to the actuating diaphragm to lift the diaphragm and open the valve. The pressure differential between the valve chamber and the outlet and the initial pressure caused by the deformed tethers are employed to increase the sealing force. The actuating device with four Z-tethers attached to the actuating diaphragm is thermally insensitive and can reduce thermally induced deflection at the center and avoid clamping effect at circumferential edge. The proposed actuating diaphragm with Z-tethers shows good thermal stability and excellent actuating performance through the finite element method (FEM) analyses. The prototype valve of 20 mm in diameter and 2 mm thick was fabricated and tested as a regulator. Using compressed air, the flow characteristics for the prototype valve were measured at different inlet pressure and elevated air temperature. The design, fabrication, simulation and characterization of the prototype valve are described.