Graphene -- the one-atom-thick form of carbon that recently won its discoverers a Nobel Prize --is very strong, nearly transparent and conducts electricity very well. But another key property is its ambipolarity; a graphene transistor’s ability to be "n-type" (negative) or "p-type" (positive) depending on whether the carrier originates from the source or drain terminals (which are effectively interchangeable) .Traditional silicon transistors usually use one or the other type of carrier, which is determined during fabrication.
This week in the online journal ACS Nano researchers from Rice University and the University of California-Riverside proposed and experimentally demonstrated a triple-mode, single-transistor graphene amplifier.
The ability of an amplifier made of graphene to be changed during operation to any of three modes at any time provides opportunities that are not possible with traditional single-transistor architectures. A third function appears when the input from each carrier is equal: The transistor becomes a frequency multiplier. By combining the three modes, the Rice-Riverside team demonstrated such common signaling schemes as phase and frequency shift keying for wireless and audio applications.
The graphene transistor also offers new opportunities for designing analog circuits with simpler structure and higher integration densities, according to the researchers.
The demonstrations were carried out by Rice professor Kartik Mohanram in collaboration with professor Alexander Balandin at the University of California-Riverside, and doctoral candidates Xuebei Yang (Rice) and Guanxiong Liu (UC Riverside). Funding for the project was provided by the National Science Foundation and the DARPA-Semiconductor Research Corporation's Focus Center Research Program.
