Implantation of carbon nanotubes in photoresist micro-channels for heat transfer applications

One of the most important applied research field associated to microfluidics deals with heat exchangers, mixers or reactors. The future electronic devices will contain more and more components, causing an increasingly heat generation that can harm internal parts of the device and requiring innovative cooling methods. Since the publication of Tuckerman and Pease [1] who first used silicon microchannels as heat exchangers, there has been a lot of works for devices including microsystems that circulate a fluid to draw heat from chips. From a heat exchange point of view, using a liquid is better than air. But the reduction of the hydraulic diameter of the microchannels involves a dramatic increase of the pressure drops. So, to assume the flow rate of the liquid, the system has to be equipped with macroscopic pumps and the benefits of reducing the size of the exchanger are lost. Using nanofluids as cooling liquid systems is a new exciting alternated way studied by many researchers [2]. Nanofluids refer to a two-phase mixture, that is a liquid in which fine metallic nanoparticules less than 50 nm in size are dispersed. Of course, easily available carbon nanotubes (CNT) are an extensively used tool for such applications. A experiment under test is to incorporate CNT into thermal grease that sits between a microprocessor and a heat sink [3]. On the one hand, the CNT conduct heat extremely well, are very small, can be suspended in liquids or polymers. One the other hand, CNT are superior thermal conductors by themselves but because of high thermal boundary resistance between the tubes and the other elements, some authors argue that they cannot exhibit the same level of high conductivity when integrated into other materials [4].