A high-flow thermopneumatic microvalve with improved efficiency and integrated state sensing

Abstract

This paper reports a thermopneumatic microvalve featuring a corrugated diaphragm. A sealed cavity below the diaphragm contains a volatile fluid, the vapor pressure of which can be increased by resistive heating to deflect the diaphragm, thus closing the valve. Silicon heater grids are elevated 9 /spl mu/m above the cavity floor, and the cavity is only partially filled with fluid, to increase thermal efficiency. A vacuum-sealed, capacitive pressure sensor on the floor allows direct monitoring of the cavity pressure. Pentane-filled actuators sustain a 2070 torr pressure rise above atmospheric with 500 mW input power. A device tested in situ closes with 350 mW at 1000 torr inlet pressure (venting to vacuum) and maintains closure with 30 mW input. Valves conduct 400 sccm under 1500 torr differential pressure, while maintaining leak rates as low as 10/sup -3/ sccm, yielding a dynamic range of 10/sup 5/. A thermodynamic model has been developed that matches experimental power, pressure, and transient response data to within a few percent. This model is used to suggest an optimized structure capable of a 2000 torr pressure rise with 50 mW input and a 1 s response time. The glass-and-silicon valve structure is suitable for integration into complete microfluidic systems.