Thermofluidics Design Evolution of Biomimetic Micropillar Wick for Thin-Film Evaporative Cooling*

Thin-film evaporative cooling in heat pipe and vapor chamber is a promising approach for passive cooling of microelectronics. This study reports the development of a capillary wick design, consisting of an array of wedged micropillars inspired by the peristome of Nepenthes alata. The sharp wedge corners lead to high meniscus curvature. The resulting large capillary pumping pressure, coupled with high permeability of the array, can achieve ~234% higher dryout heat flux compared to the cylindrical micropillar array. However, fabrication of these micropillars using optical lithography and DRIE results in large radius of curvature at the wedge corners, which significantly decreases its thermofluidic performance. We adopt several alternative fabrication approaches to improve the wedge corner sharpness, including the use of serif structures and e-beam lithography. We find that e-beam lithography achieves the requisite wedge geometry. However, upscaling the process to large footprint area is challenging. In view of these challenges, we propose a new design of wedged micropillars that compensates for finite corner radius, can be fabricated using optical lithography and DRIE, and can deliver dry-out heat flux performance equivalent to that of sharp wedge corner micropillars.