Graphene Transistors that Can Work at Blistering Speeds

IBM shows that graphene transistors could one day replace silicon.

IBM has created graphene transistors that leave silicon ones in the dust. The prototype devices, made from atom-thick sheets of carbon, operate at 100 gigahertz--meaning they can switch on and off 100 billion times each second, about 10 times as fast as the speediest silicon transistors.

Speedy switches: These arrays of transistors, printed on a silicon carbide wafer, operate at speeds of 100 gigahertz. Credit: Science/AAAS

The transistors were created using processes that are compatible with existing semiconductor manufacturing, and experts say they could be scaled up to produce transistors for high-performance imaging, radar, and communications devices within the next few years, and for zippy computer processors in a decade or so.

Researchers have previously made graphene transistors using laborious mechanical methods, for example by flaking off sheets of graphene from graphite; the fastest transistors made this way have reached speeds of up to 26 gigahertz. Transistors made using similar methods have not equaled these speeds.

Growing transistors on a wafer not only leads to better performance, it's also more commercially feasible, says Phaedon Avouris, leader of the nanoscale science and technology group at the IBM Watson Research Center in Ossining, NY where the work was carried out.

Ultimately, graphene has the potential to replace silicon in high-speed computer processors. As computers get faster each year, silicon is getting closer and closer to its physical limits, and graphene provides a promising potential replacement because electrons move through the material much faster than they do through silicon. "Even without optimizing the design, these transistors are already 2.5 times better than silicon," says Yu-Ming Lin, another researcher at IBM Watson who collaborated with Avouris.

Other researchers have made very fast transistors using expensive semiconductor materials such as indium phosphide, but these devices only operate at low temperatures. In theory, graphene has the material properties needed to let transistors run at terahertz speeds at room temperature.

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The IBM researchers grew the graphene on the surface of a two-inch silicon-carbide wafer. The process starts when they heat the wafer until the silicon evaporates, leaving behind a thin layer of carbon, known as epitaxial graphene. This technique has been used to make transistors before, but the IBM team improved the process by using better materials for the other parts of the transistor, in particular the insulator.

"Graphene's properties are very sensitive to its environment," says Lin. This is why the IBM group focused on designing a new insulating layer--the part of the transistor that prevents short circuits. They found that adding a thin layer of a polymer between the dielectric and the graphene improved performance. The work is described this week in the journal Science.