Single-use MEMS sealing valve with integrated actuation for ultra low-leak vacuum applications

Abstract

The design, modeling, fabrication and successful demonstration of a bulk-micromachined MEMS valve that enables high gas flow rates of hundreds of sccm in its initial open state and ultra low-leak, permanent sealing against gas flow once closed are demonstrated. When the valve is open, a high aspect ratio ring of solder surrounds its flow orifice without blocking the flow path. When the valve is thermally actuated by an integrated resistive heater, the solder melts and reflows, creating an irreversible seal over the flow orifice. The flow orifice is formed in a silicon ‘island’ that is supported on a thermally-insulating membrane to limit heat conduction to the surrounding silicon and to minimize the input power that is needed to close the valve. The valve’s measured open flow rate is up to approximately 400 sccm. The flow orifice is observed to seal when about 0.3 W of power are input to the resistive heater. To within the measurement uncertainty, the measured leak rate during valve testing is comparable to the measured leak rate when flow is measured through a solid plate, indicating that the valve’s leakage is less than the test system’s parasitic leakage and outgassing. The minimum, average, and maximum values of difference between the valve leak rate and the system’s parasitic leak rate are 0 sccm, 0.65 × 10–4 sccm, and 1.65 × 10–4 sccm respectively when a 1 atmosphere pressure difference is applied across the valve. The average value corresponds to an open-to-closed flow rate ratio of greater than 6 × 106. This compact sealing valve may be combined with low and high vacuum micropumps to enable MEMS vacuum systems with both initial rough evacuation and long-term high vacuum maintenance capabilities.