An electrostatically latching thermopneumatic microvalve with closed-loop position sensing

This paper presents a microvalve that combines thermopneumatic drive with an electrostatic hold, harnessing the advantages of both actuation mechanisms in a structure believed to be the first of its kind. A heater grid, elevated 10μm above the cavity floor, energizes a working fluid, raising the pressure in the cavity and deflecting the corrugated diaphragm and valve plate. A capacitive pressure sensor reads out the cavity pressure and valve seat position and provides feedback to determine when to apply the electrostatic hold voltage. Once latched, the power can be removed from the heater and, thus, the valve only requires power to transition from open to closed and consumes no static power. The thermopneumatic/electrostatic actuator combination provides high force, high speed, and low power in an 8×8mm die and is being developed for a low-power wireless gas chromatography system. The thermopneumatic actuator closes the valve in 1s at 200mW and the valve position is determined with a sensitivity of 4.3fF/Torr. The leak rate is less than 0.02sccm and the open flow is 3.3sccm at 130Torr. The electrostatic hold mechanism latches above 40V for thermopneumatic pressures greater than 600Torr.