Graphene circuit: This integrates a graphene transistor (inside the red box) with two other elements, called inductors, on a single chip. The black devices at the sides and top of the image are electrical probes.
MIT Technology Review – Researchers at IBM have made the best integrated circuits yet from graphene, a material that promises much faster components than silicon allows but which has proven difficult to work with. The team made the circuits using existing manufacturing methods, showing that graphene could be used to make faster, more power-efficient radio communications circuitry for cell phones, and other wireless devices.
The IBM researchers report methods for making graphene integrated circuits on single chips using existing methods.
The IBM group made a type of circuit called a frequency mixer, combining one graphene transistor and two metal devices called inductors. “The frequency mixer is one of the basic building blocks of analog electronics, and wireless communications in particular,” says IBM researcher Yu-Ming Lin. These devices are used in cell phones to convert the radio signal used to transmit information into another signal in a frequency range that the human ear can hear. That’s accomplished by mixing the radio signal with a reference signal.
The IBM researchers made a type of circuit commonly used in cell phones, radios and radar devices. To make the integrated circuits they had to combine graphene transistors with other, non-graphene components. This is a challenge because of the way graphene interacts with metal and other ingredients.
“This is really exciting work and it points to the rapidly approaching future of graphene electronics,” says James Tour, professor of chemistry and computer science at Rice University in Houston, Texas, who was not involved with the work.
Graphene, a single-atom-thick mesh of carbon atoms, conducts electrons much faster than silicon. Its electronic properties are such that its greatest promise is not for the digital logic circuits found in microprocessors, but for speedy analog electronics, a class of device that is commonly used to process and generate radio signals for telecommunications.
The resulting circuits operate at 10 gigahertz—much faster than previous graphene circuits. Lin concedes that they are less reliable than the state of the art silicon frequency mixers but says they expect to close that gap soon.
The IBM researchers plan to make them on the scale of tens rather than hundreds of nanometers. “They can easily be ten times smaller, which would help us surpass the record,” says Lin. “We haven’t seen the limits of graphene devices in terms of speed—we think they can get into the terahertz range.”
The next step is to improve the reliability of the circuits, says Xiangfeng Duan, professor of chemistry at the University of California, Los Angeles. “The signal comes out weaker at the other end,” he notes. “Improving the transistors will help get better circuit performance.”
The IBM group is working on this problem, and is developing more complex graphene integrated circuits. Lin says the method used for the frequency-mixer circuits will work for other types of circuits. “This is the first step towards a new level of potential,” he says. “Perhaps we won’t see the real impact of graphene for another five to ten years.”
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