February 15 2008
Is is possible to shrink to the nanometer scale transistor channel dimensions ? Can such a nano-transistor work at high frequency, how should it work and what is it good for ? To answer these questions the mesoscopic physics group of the Pierre Aigrain Laboratory has fabricated and characterized at GHz frequencies nano-transistors made of single single carbon nanotubes. With a diameter of 1-2 nanometers, a semiconducting carbon nanotube represents the most elementary transistor channel one can think of. Charge transport is provided by a single, four times degenerated, electronic mode. In the ballistic regime, it can carry up to 20 microamps with a quantified resistance of 6 kOhms. It can be efficiently controlled by a small voltage using a top gate with ultra thin oxide so that electrostatic coupling is maximized up to the quantum capacitance limit. This results in large transconductance values of 10 microSiemens, to be compared with the 0.5 µS/nm for conventional semiconductors. Such numbers were reported in DC measurements but not confirmed at high frequency due to the difficulty to perform broad-band GHz measurements on such high impedance devices. These intrinsic qualities make of the nanotube transistor an ultimate charge detector which is both sensitive and fast, therefore very attractive for future physics experiments. Being able to detect one by one electrons drifting in a quantum conductor would allow to investigate new transport regimes where quantum effects are paramount. Possible applications con be found in the fast readout of charge states of electronic devices for quantum information processing (quantum bits).
Experiments, published in January 2008 issue of Nano Letters by researchers from the mesoscopic physics group demonstrate these unique high frequency properties of nano transistors. From their data, authors infer a cut-of frequency of 50 GHz, which is a new state-of-the art for carbon nanotube transistors.
Single carbon nanotube transistor at GHz frequency
J. Chaste, L. lechner, P. Morfin, G. Fève, T. Kontos, J.-M.Berroir, C. Glattli, H. Happy, P. Hakonen, B. Plaçais
NanoLetters, 8, 525 (2008)