Active thermal cooling using liquid dielectrophoresis

On-chip cooling poses a potential challenge in semiconductor industry. Electronic devices generate more heat when scaled down and thus heat needs to be dissipated effectively. For cooling local hot spots on electronic chips, Electrowetting on Dielectric (EWOD) based droplet cooling has been adapted. But here the performance of droplet evaporation is limited by the area of cooling at a particular time. Therefore, the technology needs efficient control over the droplets in order to maximize the cooling rate. In the present work, a large hot spot area (15mm²) has been cooled using a single deionized water drop by inducing non-uniform electric field. Water droplet on two coplanar electrodes, upon applying AC voltage, experiences non-uniform electric field and spreads along the electrodes. This phenomenon, known as Liquid Dielectrophoresis (L-DEP), enables the drop to spread. Cr/Au coplanar electrodes have been patterned with 100μm gap along with a back side aligned Ti/Pt heater in the gap between the coplanar electrodes. Heat flux of 100W/cm² is applied to the heater by constant power mode and effective evaporation of the drop provides 76% of the cooling of the heated area. The power consumption for the droplet spreading is calculated as 30.2μW moving with an average velocity of 2.8 mm/s.