High-performance electronics Graphene could replace silicon in microelectronics

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Researchers at the Georgia Institute of Technology may have found the successor to silicon in semiconductor technology: epitaxial graphene. The graphene layer, also referred to as epigraphene, spontaneously forms on a silicon carbide crystal, a semiconductor used in high-performance electronics.

A pressing task in the field of nanoelectronics is the search for a material that could replace silicon. Graphene seemed promising for decades, but its potential has stagnated. As silicon approaches its speed limits, the need for the next major nanoelectronics platform is now more crucial than ever. 
Walter de Heer, a professor at the School of Physics at the Georgia Institute of Technology, has taken a significant step forward in finding a successor to silicon. De Heer and his team developed a new nanoelectronics platform based on graphene—a single layer of carbon atoms. The technology is compatible with conventional microelectronics manufacturing, a prerequisite for any viable alternative to silicon. In the course of their research, the team may have also discovered a new quasi-particle. This discovery could lead to the production of smaller, faster, more efficient, and sustainable computer chips, with potential implications for quantum and high-performance computing.

"The strength of graphene lies in its flat, two-dimensional structure held together by the strongest known chemical bonds," says de Heer. "It was clear from the beginning that graphene can be much more miniaturized than silicon—enabling much smaller devices that operate at higher speeds and produce much less heat. In principle, this means that more devices can be packed onto a single graphene chip compared to silicon." 
As early as 2001, de Heer proposed an alternative form of electronics based on epitaxial graphene or epigraphene—a graphene layer that spontaneously forms on a silicon carbide crystal, a semiconductor used in high-performance electronics. At that time, researchers discovered that electrical currents flow without resistance along the edges of epigraphene, and graphene components can be seamlessly connected without metal wires. This combination enables electronics that harness the unique light-like properties of graphene electrons.

"Quantum interference has been observed in carbon nanotubes at low temperatures, and we expect to see similar effects in epigraphene ribbons and networks," said de Heer. "This crucial property of graphene is not possible with silicon."

Structure of the platform

To create the new nanoelectronics platform, the researchers developed a modified form of epigraphene on a silicon carbide crystal substrate. In collaboration with researchers from the Tianjin International Center for Nanoparticles and Nanosystems at Tianjin University, China, they produced unique silicon carbide chips from electronics-grade silicon carbide crystals. The graphene itself was grown in de Heer's laboratory at Georgia Tech in patented furnaces.

The researchers utilized electron beam lithography, a common method in microelectronics, to etch the graphene nanostructures and weld their edges to the silicon carbide chips. This process mechanically stabilizes and seals the graphene edges that would otherwise react with oxygen and other gases, potentially disrupting the movement of charges along the edge. 
To measure the electronic properties of the graphene platform, the team eventually employed a low-temperature apparatus capable of recording properties from a temperature near absolute zero to room temperature.

Observation of the edge state

The electric charges observed by the team at the edge state of graphene resembled photons in an optical fiber, capable of traveling long distances without scattering. They found that the charges traveled over tens of thousands of nanometers along the edge before scattering occurred. In previous technologies, graphene electrons could only travel about 10 nm before encountering small imperfections and scattering in different directions. 
"What's special about the electric charges at the edges is that they stay at the edge and move at the same speed, even if the edges are not perfectly straight," said Claire Berger, a physics professor at Georgia Tech and research leader at the French National Center for Scientific Research in Grenoble, France.

In metals, electric currents are carried by negatively charged electrons. Contrary to the researchers' expectations, their measurements suggested that the edge currents were not carried by electrons or holes (a term for positive quasi-particles indicating the absence of an electron). Instead, the currents were carried by an extremely unusual quasi-particle that has no charge and no energy yet moves without resistance. The components of this hybrid quasi-particle moved on opposite sides of the graphene edges, although it is a single object. 
The unique properties suggest that the quasi-particle could be one that physicists have been hoping to harness for decades—the elusive Majorana fermion predicted by the Italian theoretical physicist Ettore Majorana in 1937. "The development of electronics utilizing this new quasi-particle in seamlessly connected graphene networks is groundbreaking," says de Heer. 
According to de Heer, it will likely take another five to ten years before the first graphene-based electronics become possible. However, thanks to the team's new epitaxial graphene platform, the technology is closer than ever to crowning graphene as the successor to silicon.