IBM Research is claiming the world's fastest graphene field-effect transistor (FET), operating at 26 GHz.

Researchers at IBM's Thomas J. Watson Research Center (Yorktown Heights, N.Y.) predicted that the higher electron mobility of carbon will eventually propel the material beyond the reach of silicon into the terahertz range greater than 100 GHz.

"We have measured the fastest speed for any graphene transistors to date, 26 gigahertz, with a gate length of 150 nanometers," said Phaedon Avouris, IBM Fellow and manager of Nanometer Scale Science and Technology. "Since peak frequency increases with reduced gate length, we believe terahertz graphene transistors may be achievable by further reducing gate lengths to about 50 nanometers."

Graphene is composed of the same substance as nanotubes, chicken wire-like "honeycomb" lattices of carbon atoms. However, instead of bending the honeycomb lattices into nanoscale tubes that are difficult to fabricate, graphene transistors are made by depositing carbon atoms as a thin film that can be patterned with traditional lithographic tools.

IBM has already demonstrated by-layer deposition techniques that solve noise problems associated with using narrow ribbons of graphene as transistors channels. In the most recent demonstration, IBM claims that terahertz-range frequencies required for millimeter-wavelenth communications circuits are within the reach of graphene thin films.

IBM said its top-gated graphene transistors were fabricated using silicon-on-insulator wafers, then characterized for high-frequency operation at various gate voltages and gate lengths. The results show that current gain in graphene transistors follow a traditional decreasing FET response curve with increasing frequency.

The peak cut-off frequency was found to be inversely proportional to the square of the gate length, with 26 GHz at 150 nanometers the highest frequency achieved.

The Defense Advanced Research Projects Agency (Darpa) sponsored parts of the research under a carbon electronics for RF applications program. The Darpa program aims to develop millimeter-wavelength communications technologies with an ultimate goal of demonstrating W-band, low-noise amplifiers operating at 100 GHz or higher using graphene thin-film transistors on 8-inch or larger wafers.

The IBM team will next seek to improve its gate dielectric materials with the goal of demonstrating working RF circuits operating in the terahertz range.

By: DocMemory
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