Image of a 1.6 nanometer wide metal-like graphene nanoribbon (Graphene Nanoribbon, GNR) taken with a scanning tunneling microscope .
Transistors based on carbon rather than silicon can potentially speed up computers and reduce their power consumption by more than a thousandfold - think, for example, of a mobile phone that holds a charge for months. But the range of materials needed to create working carbon chains has remained incomplete to this day.
A team of chemists and physicists at the University of California, Berkeley have finally created the last missing piece - a wire made entirely of carbon. This, in turn, paved the way for research into carbon-based transistors, and ultimately computers.
Felix Fischer, a professor of chemistry at the University of California, Berkeley, noted that the ability to fabricate all IC elements from a single material would make manufacturing easier:
"This was one of the key points that was missing in the overall picture of the architecture of all-carbon ICs."
Metallic wires are used to connect transistors in a computer chip - they carry electricity from device to device and connect semiconductor elements inside a chip block.
A group at the University of California, Berkeley has been working for several years on how to make semiconductors and insulators from graphene nanoribbons, which are narrow, one-dimensional strips of graphene as thick as an atom. The structure of these nanoribbons is entirely composed of carbon atoms arranged in a hexagonal system that resembles a wire mesh.
While other carbon-based materials such as 2D graphene sheets and carbon nanotubescan be metal-like, they have their drawbacks. For example, converting a sheet of 2D graphene into nanometer-sized strips can turn them into semiconductors or even insulators. Carbon nanotubes, which are excellent conductors, cannot be produced with the same precision in large quantities as nanoribbons.
“Nanoribbons allow us to access a wide variety of structures using bottom-up design that is not yet possible with nanotubes,” said Michael Crommy, professor of physics at the University of Berkeley. “It allowed us to link electrons together to create a conductive nanoribbon, which was not done before. This is one of the big challenges in graphene nanoribbon technology, and that's why we are so excited about it. "
Metal-like graphene nanoribbons have a wide, partially filled electronic band, typical of metals, and can be comparable in conductivity to two-dimensional graphene.
“This is the first time that we can create an ultra-thin conductor from carbon-based materials and this is a real breakthrough,” added Fischer.
Crommy, Fisher and their colleagues at the University of California, Berkeley and the Berkeley National Laboratory published their findings in the September 25 issue of Science.
Silicon-based integrated circuits have been used in computers for decades, regularly increasing in speed and performance according to Moore's Law, but they are already reaching their speed limit for how quickly they can switch between "ones" and "zeros". It also becomes more and more difficult to reduce energy consumption; computers already consume a significant portion of the world's energy production. Carbon-based computers can potentially switch many times faster than silicon computers and consume only a fraction of their energy, Fisher said.
Graphene, which is pure carbon, has been the leading contender for the next generation of carbon-based computers. However, the narrow strips of graphene are primarily semiconductors, and the challenge was getting them to work as insulators and metals as well in order to build carbon-based transistors.
Several years ago, Fischer and Crommy teamed up with material theorist Stephen Louis, professor of physics at the University of California at Berkeley, to discover new ways to connect small pieces of nanoribbon while preserving all conductive properties.
Two years ago, the team demonstrated that by correctly connecting short nanoribbon segments, electrons in each segment can be positioned to create a new topological state - a distinct quantum wave function - resulting in tunable properties of the semiconductor.
In their new work, they use a similar technique to "stitch" short segments of nanoribbons together to create a conductive metal-like wire tens of nanometers long and only one nanometer wide.
“They are all designed in such a way that they can only be combined with each other in one way. It's as if you take a Lego bag, shake it, and have a fully assembled car, ”he said. "This is the magic of self-assembly control with chemistry."
“Through chemistry, we made tiny changes to one chemical bond for every 100 atoms, and we increased the nanoribbon's conductivity by 20 times. And it's important from a practical point of view to get good metal that way, ”said Crommy.
“I believe this technology will revolutionize the way we build integrated circuits in the future,” Fischer said. “This will be a big step forward in electronics design and manufacturing, compared to what you would expect from silicon right now. We now have the ability to get faster performance with much less power consumption. This will be the driving force behind the future of the electronic semiconductor industry. "