A Flat Heat Pipe Architecture Based on Nanostructured Titania

A novel 3 cm x 3 cm x 600 mu m-thick Ti-based flat heat pipe is developed for Thermal Ground Plane (TGP) applications. The Ti-based heat pipe architecture is constructed by laser welding two microfabricated titanium substrates to form a hermetically sealed vapor chamber. The scalable heat pipes' flat geometry facilitates contact with planar heat sources, such as microprocessor chip surfaces, thereby reducing thermal contact resistance and improving system packaging. Fluid transport is driven by the wicking structure in the TGP, which consists of an array of Ti pillars that are microfabricated from a titanium substrate using recently developed high-aspect-ratio Ti processing techniques [1]. The hydrophilic nature of the Ti pillars is increased further by growing similar to 200-nm hairlike nanostructured titania of the pillar surfaces. The resulting super hydrophilic wick offers the potential to generate high wicking velocities of similar to 27.5 mm/s over distances of 2 mm. The experimental wetting results show a diffusive spreading behavior that is predicted by Washburn dynamics [2]. The maximum effective thermal conductivity of a heat pipe is directly related to the speed of capillary flow of the working fluid through the wick and is measured experimentally in the first-generation device to be k = 350 W/m . K. A dummy TGP with a cavity volume of similar to 170 mu L was used to test the hermiticity level of the laser packaging technique. The device gave a 0.067% of water loss based on similar to 60 mu L of charged water at 100 degrees C in air for over a year. [2009-0303]