NEW YORK, US: Research to reduce copper pathways that transport electricity and information around the labyrinth of transistors and components. When these pathways, called interconnects, grow smaller, they become less efficient, consume more power, and are more prone to permanent failure. To overcome this hurdle, industry and academia are vigorously researching alternative to succeed traditional copper as the material of choice for interconnects on computer chips. One such alternative is graphene, an atom-thick sheet of carbon atoms arranged like a nanoscale chicken-wire fence. Graphene is essentially a single layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques.
A team led by Saroj Nayak, Professor, Rensselaer Polytechnic Institute, discovered they could enhance the ability of graphene to transmit electricity by stacking several thin graphene ribbons on top of one another.
“Graphene shows enormous potential for use in interconnects, and stacking up graphene shows a viable way to mass produce these structures,” said Nayak.
“Copper’s limitations are apparent; as increasingly smaller copper interconnects suffer from sluggish electron flows that result in hotter, less reliable devices. Our new study makes a case for the possibility that stacks of graphene ribbons could have what it takes to be used as interconnects in integrated circuits.”
The study, based on large-scale quantum simulations, was conducted using the Rensselaer Computational Center for Nanotechnology Innovations (CCNI).
Copper interconnects suffer from a variety of unwanted problems, which grow more prominent as the size of the interconnects shrink. Electrons travel through the copper nanowires sluggishly and generate intense heat. As a result, the electrons “drag” atoms of copper around with them. These misplaced atoms increase the copper wire’s electrical resistance, and degrade the wire’s ability to transport electrons. This means fewer electrons are able to pass through the copper successfully, and any lingering electrons are expressed as heat. This heat can have negative effects on both a computer chip’s speed and performance.
Nayak’s recent work is titled “Effect of Layer Stacking on the Electronic Structure of Graphene Nanoribbons.” When cut into nanoribbons, graphene is known to exhibit a band gap — an energy gap between the valence and conduction bands—which is an unattractive property for interconnects. The new study shows that stacking the graphene nanoribbons on top of each other, however, could significantly shrink this band gap.
“The optimal thickness is a stack of four to six layers of graphene,” said Neerav Kharche, first author of the study and a computational scientist at CCNI. “Stacking more layers beyond this thickness doesn’t reduce the band gap any further.”
The end destination, Nayak said, is to one day manufacture microprocessors — both the interconnects and the transistors — entirely out of graphene. This game-changing goal, called monolithic integration, would mean the end of the long era of copper interconnects and silicon transistors.
© Rensselaer Polytechnic Institute News