Professor Johan Liu's team showed a couple of years ago that graphene can have a cooling effect on silicon-based electronics. "But the methods that have been in place so far have presented the researchers with problems", he said. "It has become evident that those methods cannot be used to rid electronic devices off great amounts of heat, because they have consisted only of a few layers of thermal conductive atoms.
"When you try to add more layers of graphene, another problem arises, a problem with adhesiveness. After having increased the amount of layers, the graphene no longer will adhere to the surface, since the adhesion is held together only by weak van der Waals bonds."
"We have now solved this problem creating strong covalent bonds between the graphene film and the surface, which is an electronic component made of silicon."
The stronger bonds result from the addition of a property-altering molecule. Having tested several different additives, the Chalmers researchers concluded that adding (3-Aminopropyl) triethoxysilane (APTES) molecules had the most desired effect. When heated and put through hydrolysis, it created silane bonds between the graphene and the electronic component.
Moreover, functionalisation using silane coupling doubles the thermal conductivity of the graphene. The researchers have shown that the in-plane thermal conductivity of a 20µm thick graphene based film can reach a thermal conductivity value of 1600W/mK – four times that of copper.
"Increased thermal capacity could lead to several new applications for graphene," says Johan Liu. "One example is the integration of graphene-based films into microelectronic devices and systems, such as highly efficient LEDs, lasers and RF components for cooling purposes. Graphene-based film could also pave the way for faster, smaller, more energy efficient, sustainable high power electronics."
