1/f noise in carbon nanotube devices - On the impact of contacts and device geometry

We report on the 1/f noise in various ballistic carbon nanotube devices. A common means to characterize the quality of a transistor in terms of noise is to evaluate the ratio of the noise amplitude A and the sample resistance R. By contacting semiconducting tubes with different metal electrodes we are able to show that a small A/R value by itself is no indication of a suitable metal/tube combination for logic applications. We discuss how current in a nanotube transistor is determined by the injection of carriers at the electrode/nanotube interface, while at the same time excess noise is related to the number of carriers inside the nanotube channel. In addition, we demonstrate a substantial reduction in noise amplitude for a tube transistor with multiple carbon nanotubes in parallel.