Low-Frequency Noise Spectroscopy at Nanoscale: Carbon Nanotube Materials and Devices
Article appeared as chaper in: Carbon Nanotubes Applications on Electron Devices, INTECH, edt. J. M. Marulanda, p.257-298
S. Vitusevich and F. Gasparyan
Published: August 2011
In this review we describe noise properties of carbon nanotube based materials and devices. After brief introduction in peculiarities of transport and noise properties of CNTs we discuss main noise components and theoretical models of the flicker noise directly related with conductivity of the materials. Then we review noise properties of individual CNTbased structures, which are considered to be the best from a nanoscale fundamental studies point of view. They have a cylindrically perfectly ordered shape almost without defects in the structure. We will show that the noise characteristics of CNTs are competitive to conventional materials, but many new features of transport can be revealed as a result of the nanoscale sizes of the nanotube. These objects are good for the modeling of the physical properties of any new kind of materials at the nanoscale. Then we will continue to describe the properties of carbon nanotube thin films. These structures, tunable at the nanoscale but still exhibiting quasi-bulk properties, are promising since they are flexible for different kinds of applications such as high-speed or impedance matched devices. In spite of the progress in their production technology the noise level is still high due to the excess noise produced as a result of fluctuations in the tube-tube junctions. Next we will describe noise properties in parallel aligned nanotube channels. The structures demonstrated reduced noise properties. We will discuss our efforts to improve the properties of the CNT-FETs using gamma radiation treatment. Our analysis shows that the difference in output characteristics of the FETs before and after small doses of gamma radiation treatment is due to a reduced contribution to the total current parallel to the nanotube resistance. It should be emphasized that the transconductance of the CNT-FETs and level of noise did not change strongly after the treatment with a dose of 1x104 Gy and 2x104 Gy. Moreover our results show that active gamma-radiation treatment can improve the transport and noise properties of CNT-FETs at a small optimal dose. The radiation treatment was found to decrease the influence of parasitic conduction channels on transport characteristics of the device. The Hooge parameters obtained are comparable to typical values obtained for conventional semiconductors. After that we will briefly give an overview on results of transport studies on CNT-based structures using shot noise. Finally we will draw the main conclusions and give a short outlook for the potential of noise spectroscopy as the basis for novel technology development.