Design, fabrication, and testing of micromachined silicone rubber membrane valves

Abstract

Technologies for fabricating silicone rubber membranes and integrating them with other processes on silicon wafers have been developed. Silicone rubber has been found to have exceptional mechanical properties including low modulus, high elongation, and good sealing. Thermopneumatically actuated, normally open, silicone rubber membrane valves with optimized components have been designed, fabricated, and tested. Suspended silicon nitride membrane heaters have been developed for low-power thermopneumatic actuation. Composite silicone rubber on Parylene valve membranes have been shown to have low permeability and modulus. Also, novel valve seats were designed to improve sealing in the presence of particles. The valves have been extensively characterized with respect to power consumption versus flow rate and transient response. Low power consumption, high flow rate, and high pressure have been demonstrated. For example, less than 40 mW is required to switch a 1-slpm nitrogen flow at 33 psi. Water requires close to 100 mW due to the cooling effect of the liquid. [427]

A review of microvalves

“…Bimetallic. The use of thermally actuated microvalves, such as bimetallic [66,67], thermopneumatic [68][69][70][71][72][73][74][75] and shape memory alloy actuations [76][77][78][79][80][81][82], considerably increases the force available from microstructures while simultaneously achieving large strokes. Although drawbacks include relatively slow actuation speed and high power consumption due to temperature changes, thermal actuation schemes are attractive because of the simplicity in microstructures.…”

“…With an inlet pressure of 20 kPa, the power to close was 200 mW while the power to reopen was 85 mW, showing hysteresis due to sticking of PDMS. Yang et al [71,72] developed a normally open microvalve using a composite membrane and 3M Fluorinert fluids for thermopneumatic actuation as shown in figure 4. The composite membrane comprising silicone rubber and Parylene C showed great impermeability for an effective vapor barrier and flexibility for large strokes with a membrane deflection of 134 µm at 28.3 kPa.…”

“…The manifolds were connected to external solenoid valves for pneumatic air pressure and vacuum actuation. Samples were loaded from an inlet port by opening the valve using vacuum (4 kPa) and pressing the samples underneath the 150 µm thick latex membrane using pressure (69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83). Vacuum was simultaneously applied to a hydrophobic vent to evacuate the air from the chamber.…”

Measurements of residual stresses in the Parylene C film/silicon substrate using a microcantilever beam

“…Note that the sign of curvature in equation 8is opposite to that in [38]. Considering the presence of the initial curvature of the cantilever before film deposition, the effective curvature 1/r induced by the film deposition process and the mismatch between the film and substrate is 1/r = 1/r A −1/r B , where 1/r A and 1/r B are the curvatures of microcantilever after and before film deposition, respectively.…”

Note: A low leakage liquid seal for micromachined gas valves

“…In order to address this issue, researchers have explored the use of soft sealing materials for the valve seat. 7,8 While such polymeric seals are suitable for a variety of valves and applications, the incorporation of such materials can be a significant challenge for other valves. The operating conditions and environments for certain valves may also limit the use of polymeric valve seats.…”