Graphene Metal Sandwich Improves Electronics

Heat conducting properties of the metal Copper are well known. However, scientists have been able to improve this property even further. By creating a sandwich of graphene with copper, scientists have found that the heat conducting properties of copper are strongly enhanced. Expectedly, this discovery could lead to further downscaling of electronic products.

This pioneering discovery is the work of two professors – Alexander A. Balandin and Konstantin S. Novoselov. Balandin is a professor of electrical engineering at the Bourns College of Engineering at the University of California, Riverside. Novoselov is a professor of physics at the University of Manchester in the United Kingdom. Both are corresponding authors for the paper they have published in the journal Nano Letters.

In their experiments, the researchers added a one-atom thick graphene layer on both sides of a copper film. The graphene layer had highly desirable mechanical, thermal and electrical properties. The researchers found that the addition of graphene layers on the two sides of the copper film increased the heat conducting properties of the sandwich by up to 24 percent.

According to Balandin, who initially discovered the unusual heat conducting properties of graphene in 2013, the enhancement of the ability of copper to conduct heat was an important discovery. Hybrid copper-graphene interconnects in electronic chips could now be made much smaller.

Copper is the most popular metal used for semiconductor interconnects and it replaced aluminum because of its better electrical conductivity. Layering copper with graphene and increasing the heat conducting properties of copper, therefore, became an important factor for the electronic industry.

Manufacturers tend to downscale the size of interconnects and transistors in computer chips with the intention of increasing the number of transistors therein. This puts an enormous strain on the performance of the copper interconnects they use. Downscaling had reached a point where there is little room for further improvement. Therefore, manufacturers were actively seeking improved interconnect structures with better conduction properties for current and heat.

Initially, even the researchers were surprised at the significant improvement in the thermal conduction properties of copper film despite the thickness of the graphene coating being only one atom thick. However, they soon realized that the improvement was not from the graphene acting as an additional heat-conducting channel. Rather, the improvement came about as changes occurred in the copper’s Nano- and microstructure because of the graphene layer deposition.

Researchers used microscopes to examine the grain sizes within the copper film both before and after adding graphene. They found that the high temperature deposition of graphene, in vapor form, stimulated the growth of grain sizes in the copper film. Ultimately, it was found the larger grain sizes in the copper coated with graphene that caused the improvement in heat conduction.

Another finding of the research was the improvement in heat conduction of copper was limited to thin copper films alone. This is a significant find since the future copper interconnects will be scaling down to the nanometers range. A nanometer is one-thousandth of a micrometer. Balandin and his team will be researching the heat conduction properties in copper films of nanometer thickness coated with graphene.