One-dimensional carbon nanotube-based field effect transistors (CNTFET) are among the most promising molecular electronic devices. With semiconductor carbon nanotubes (CNT), which have unprecedented carrier mobility as a channel material, these nanoscale transistors are already competitive with silicon-based devices (Appl. Phys. Lett. 80,3817 (2002)).

In this project, we investigate a CNTFET with a metallic CNT playing role of a top-gate (a schematic figure of the device is shown in figure 1, upper image). Reducing the gate length is well known to improve performance of FETs; while metallic gate length would be limited by lithography resolution of about 20 nm, using a CNT as a gate readily provides the gate length of just 1-2 nm.

We have developed a theoretical model that combines a description of diffusive charge transport in semiconducting CNT channel with accurate simulation of electrostatic potential in the whole device. Using the model, we have demonstrated and explained a superior performance (sharper and faster switching) of the CNTFET modulated by CNT gate in comparison to the planar back-gate (see figures 2 and 3); the theoretical results are in a good agreement with measurements on an experimental device which has been fabricated and characterized at the Atomic Physics group at the University of Gothenburg (an AFM image of the experimental device is shown in figure 1, lower image). Remarkably, a short switching time of 5 picoseconds has been demonstrated, which means that the CNTFET can operate at frequencies up to 200 GHz.

We have also studied the FET performance scaling with the device geometry; in particular, we have shown that for experimentally feasible geometry, the sharpness of switching close to thermal limit and the switching time of 1.4 ps can be reached (see figure 4).

The project was supported by the Swedish Foundation for Strategic Research and the European Union through the NanoRF project.

A detailed description of the results can be found in Nanotechnology 19, 325201 (2008).