Electrowetting Droplet Manipulation for Application in Thermal Management of Compact Microsystems

Digitized heat transfer (DHT), a novel active management technique for high power density electronic and integrated micro systems in which heat is transported by a discrete array of electrostatically activated microdroplets, is proposed. Liquids, especially liquid metals or alloys, support significantly higher heat transfer rates than classical air-cooled heat sinks; in addition, discrete microdroplets are shown to be actuated and controlled with a high degree of precision and programmability. As a consequence, DHT is a viable new alternative for achieving the most important objectives of electronic cooling, i.e., minimization of the maximum substrate temperature, reduction of the substrate temperature gradient and removal of substrate hot spots. Three methods of microdroplet actuation, electrowetting on dielectric (EWOD), dielectrophoresis (DEP), and continuous electrowetting (CEW), are described, with simple results for steady state velocities in terms of known parameters. The use of EWOD to transport a droplet of commercially available liquid metal is reported. In addition, preliminary considerations on the heat transfer rates of such droplets are presented, with a simple analysis leading to a generalization of the continuous Nusselt number to a discretized flow.