Experiment and modeling of microstructured capillary wicks for thermal management of electronics

Novel thermal management approaches are desired due to the ever-increasing power densities in high-performance microelectronics. The rising power density along with the shrinking real estate in these devices results in a substantial increase in device temperature beyond the typical operating temperatures required for a reliable performance. For the typical silicon based technology, efficient thermal management schemes with high heat transfer coefficients such that heat fluxes in excess of ≈ 100 W / cm² can be dissipated without severely exceeding normal operating temperatures of ≈ 80°C are desired. State-of-the-art single phase cooling technologies that rely on sensible heat are bulky and insufficient under these conditions. As a result, liquid-vapor phase change based novel thermal management solutions which utilize latent heat of vaporization of a fluid for high heat transfer with little temperature increase are needed. In this work, we present a multiphase thermal management scheme where we use arrays of cylindrical micropillars of silicon for thin-film evaporation. The microstructures maintain a continuous liquid supply via capillary pressure while controlling the liquid film thickness and the associated thermal resistance. A variety of silicon samples with various wick geometries were fabricated using standard contact photolithography and deep reactive ion etching. Effects of micropillar diameter, pitch, height and the array length on the maximum heat dissipation capability before dry-out were investigated. An analytical model was developed to predict the experimentally observed values of the evaporative heat flux. While the parametric effects of micropillar geometry were qualitatively captured by the model predictions, quantitative predictions could not be achieved due to the limitations in the experimental setup. These preliminary results suggest the potential of thin-film evaporation on microstructured surfaces for advance- thermal management applications.