Wafer-Scale Hierarchically Textured Silicon for Surface Cooling

摘要

Conventional surface materials for cooling systems, often based on metals, generally offer excellent mechanical and thermal conduction properties. However, metals are known to be very reflective, and their emissivity is very low, which limits effective radiative heat transfer from the surface to the environment - a factor that is particularly important when there is a high difference in temperature between the surface and ambient. Here we will demonstrate a novel material coating based on silicon that will offer transformative surface cooling and omniphobic properties by controlling the microscale surface texture on silicon wafers. Surface texturing silicon or micro-structuring silicon using maskless chemical assisted etching or reactive-ion etching has received much attention recently for its applications in photonics and solar cells ^1-3. Colloquially referred to as “black silicon”, textured silicon surfaces comprised of micro-structured pillars or roughness have been known to absorb (or emit) light very effectively in the visible spectrum, which makes the surface turn black^4-6. Past studies have focused on the modified optical properties in the visible to near-infrared spectrum (400nm to 1.3um), relevant mostly to photonic applications, but we show that the optical properties maintain a high emissivity across the near-mid IR spectrum of 9-13 uM. The high emissivity across the mid-IR creates a unique opportunity to produce an inexpensive, highly adaptable, and scalable layer which demonstrates enhanced passive surface cooling relative to conventional materials. We will demonstrate a novel maskless process that utilizes a NaOH wet etch which generates micro-pyramidal structures on the order of 5-20 um in height that accomplishes these objectives. Furthermore, by texturing the surface geometry, textured silicon can also be manufactured to offer either hydrophobic or hydrophilic properties, opening the possibility for a material that can have optimized conductive, radiative, and convective properties.