Energy minimization-based analysis of electrowetting for microelectronics cooling applications

Electrowetting (EW)-induced droplet motion has been studied over the last decade in view of its promising applications in the field of microfluidics. The objective of the present work is to analyze the physics underlying two specific EW-based applications for microelectronics thermal management. The first of these involves heat absorption by liquid droplets moving on the surface of a chip under EW actuation. Droplet motion between two flat plates under the influence of an electrowetting voltage is analyzed. An energy minimization framework is employed to predict the actuation force on a droplet. This framework, in combination with semi-analytical models for the forces opposing droplet motion, is used to develop a model that predicts transient EW-induced droplet motion. The second application is targeted at hot-spot thermal management and relies on the control of droplet states on artificially structured surfaces through an applied EW voltage. The influence of an electrowetting voltage in determining and altering the state of a static droplet resting on a rough surface is analyzed. An energy minimization-based modeling approach reveals the influence of interfacial energies, surface roughness parameters and electric fields in determining the apparent contact angle of a droplet in the Cassie and Wenzel states under the influence of an EW voltage. The model is used to establish preliminary criteria to design rough surfaces for use in the hot-spot mitigation application. The concept of an electrically tunable thermal resistance switch for hot-spot cooling applications is introduced and analyzed.