Test Channels for Flow Characterization of Processed Plastic Microchannels
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available with a variety of material properties. The common methods of fabricating polymer devices (e.g., molding, stamping) are simpler than traditional micromachining, although the molds must still be made using standard IC techniques [2]. Indeed, most of the plastics processing can be done outside of the processing lab, minimizing the resources required to manufacture them. A clean, dry lab is all that is required. Molding techniques use relatively low temperatures (under 200 °C) and no harsh chemicals, which allows the possibility of the introduction of biological materials to the surfaces of polymer devices for added functionality. Furthermore, certain packaging problems, such as sealing and loading (coupling to external fluid sources), are easier to solve using polymers, since these materials tend to be more conformal than ceramics and silicon. Some problems with polymer-based chips arise however. Since most plastics are hydrophobic, chemical loading can sometimes be difficult, and external pressure sources are often required to overcome capillary repulsion (with glass, capillary forces aid in the loading). Furthermore, this hydrophobicity can also lead to bubble formation during loading, which for most microfluidic devices will cause the device to fail. In addition, under some conditions, many plastics will outgas causing bubble formation in situ-an undesired result. Flaws in processing can yield undesired artifacts which can affect the flow of fluid, or even provide leaks between channels. It is desired to be able to test the flow within the fluidic
253 Mat. Res. Soc. Symp. Proc. Vol. 605 ©2000 Materials Research Society
channels during the manufacture to assess the quality of the construction before proceeding. In the case of multilayer systems, it is desirable to be able to scan below one layer to the next. We believe that such quality control and performance characterization are required before full scale commercialization of complex chips will be feasible. In this paper we demonstrate the performance of polymer fluidic chips using capillary electrophoresis, then describe some of the problems with loading fluids in such chips, noting the likely problem areas for bubble formation, and sealing issues. Furthermore, we demonstrate the use of Optical Coherence Tomography (OCT) and Optical Doppler Tomography (ODT) for characterizing the quality and performance of micromachined plastic fluidic chips. We believe that such a characterization device could be extremely useful for development of new chip
designs and for quality control monitoring during chip manufacture in a production environment. EXPERIMENT Chip manufacture Polymer chips were manufactured at the UCI Integrated Nanosystems Research Facility by cast molding silicone rubber. The method has been in use by several groups for some years, and has been documented in the literature [3]. Silicon molds (negative pattern) were made by etching nitride coated silicon wafers. Traditional lithography was used to pattern photoresist on the nitride which was th
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