An electrostatic microvalve for pneumatic control of microfluidic systems

An electrostatic microvalve for the pneumatic control of microfluidic devices is designed, modeled, fabricated, and characterized. The valve consists of several, individually manufactured pieces assembled to form a microvalve. This creates an inexpensive microvalve that can be easily and quickly manufactured. The unique feature of this microvalve is its ability to be integrated with a microfluidic system for good portability. The valve was manufactured by depositing a thin chrome layer on a Poly(methyl methacrylate) substrate. Thin copper foil was used as a flexible membrane that would deflect to allow air flow. When a voltage was applied between the chrome layer and the copper foil, the electrostatic force pulled the foil closed against the substrate and stopped the air flow. Parylene C was selected as a dielectric layer to provide insulation and prevent short circuiting between the chrome and copper electrodes. The valve was designed using a flexible, proximal electrode concept that decreased the required closing voltage. A mathematical model was developed to predict the voltage required to close the valve. Tests were performed to determine the closing voltage and flowrate through the valve. The parylene dielectric thickness and the valve cavity depth were varied to find the best valve parameters. It was determined that a valve with a 6 mum layer of parylene with a 58 mum cavity depth provided the best combination of low closing voltage and high flowrate. These valves were tested to work at pressures up to 40 kPa with an average closing voltage of 680 V and an average flowrate of 1.05 mL/min. The valve showed that it also may be able to function as a flowrate control valve at higher pressures, i.e., greater than 40 kPa. It was found that dielectric charging was occurring in the valve during operation. Switching the polarity of the control voltage with each actuation was a proposed solution that was tested and found to delay the onset of dielectric charging. Finally, the valve was successfully used to pneumatically control flow in a simplified microfluidic device.