Carbon nanotubes and graphene for various applications in electronics: Competition and synergy

Although carbon nanotubes have been actively studied for electronics applications during the past 2 decades (1), transistors made with those materials are still plagued by a number of problems, such as contact reproducibility, large hysteresis in the transfer characteristics as well as low on-current and large off-current values, to name a few. Single walled carbon nanotubes (SWNTs) were first considered as potential candidates for the replacement of Si MOS type transistors in VLSI circuits. However the main field of application of SWNTs is shifting towards large area electronics on flexible, plastic-type substrates (2, 3), a domain which is at present, less demanding in terms of device dimensions and integration density. In particular, random networks of SWNTs, which can be obtained by solution-processing or grown at low temperature by plasma enhanced chemical vapour deposition (PECVD), represent an attractive and viable option for the fabrication of electronic devices and circuits on non-refractory substrates (4). Also, since carrier injection in carbon nanotube field effect transistors (CNTFETs) is controlled by Schottky barriers at the nanotube/metal contacts, CNTFETs can be used for gas sensing applications (5). This is a consequence of poor “wetting” of most metals on the surface of SWNTs, thus allowing gas molecule to diffuse at the interface and modify the alignment of Fermi levels by introducing surface dipoles. Finally, SWNT random arrays will probably find applications in transparent conducting films (TCFs), see ref. 6, replacing some of the oxide-based films, particularly those incorporating indium, an element whose availability on earth is limited.