THE DESIGN, MODELING, FABRICATION, AND CHARACTERIZATION OF AN EWOD ACUTATED MICROTHERMAL SWITCH
McLanahan, Aric Ranen
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In this work, a MEMS microthermal switch was designed, modeled, fabricated, and characterized thermally and dynamically. The thermal switch is based on the bulk actuation of electrowetting on a dielectric (EWOD). The switch operates by manipulating thermally conductive paths internal to the switch by changing the physical location of glycerin droplets. When the droplet is aligned between the bottom and top parts of the switch, heat flows readily. When the droplet is actuated by EWOD onto thin, thermally-isolating membranes, the flow of heat through the switch is retarded. The dynamics of the switch were modeled by determining the driving force of EWOD on a droplet, and balancing it against the forces that oppose motion. This yielded an easy to implement dynamic model for predicting droplet speeds and energy consumption. The droplet was modeled thermally by constructing a thermal resistance network and through 3D finite difference modeling. Thermal resistance off-to-on ratios greater than 10 were predicted.Prototype thermal switches were fabricated using standard silicon technology in the microfabrication facility at Washington State University. The dynamic prototype utilized transparent titanium electrodes on glass slides, and the finished thermal switch prototype was fabricated on silicon. To characterize the switch, dynamic and thermal experiments were conducted. The speeds of water and glycerin droplets were measured at 120, 60, and 30 microns at increasing applied voltages. Bulk droplet speeds of up to 4.1 mm/s were obtained. The dynamic measurements were in good agreement with the dynamic model. The thermal experiment measured the temperatures and thermal resistance through the switch at 760, 10, 1.0, and 0.6 Torr, at gap thickness of 120, 60, and 30 microns using glycerin as the working fluid. Thermal resistance ratios of 13.4 were measured for a 30 micron gap at a pressure of 0.6 Torr.