CMOS compatible synthesis of carbon nanotubes

Ayre, G.N., Smith, D.C., Mazumder, B., Hector, J., Uchino, T., de Groot, C.H. and Ashburn, P. (2007) CMOS compatible synthesis of carbon nanotubes. Materials Research Society Conference, San Francisco, United States. 24 - 27 Mar 2007.

Abstract

Traditionally, carbon nanotube (CNT) growth involves the use of transition metal nanoparticles as a catalyst. However, the integration of CNT synthesis based on metal catalysts with CMOS technology is very problematic due to the detrimental effect of transition metals on silicon device performance. Transition metals, such as Ni or Fe, create deep level defects in the silicon band gap and result in unwanted trap states [1, 2]. Other drawbacks include the high propensity of silicon-metal inter-diffusion, leading to the formation of silicides. In order to reap the benefits of silicon very-large-integration (VLSI) technology, an alternate approach is required. This work reports metal free-growth of carbon nanotubes, with a process compatible with current silicon VLSI technology, using chemical vapour deposition of CNTs on germanium nanoparticles. Various approaches to germanium catalyst preparation, based upon standard CMOS processes, are compared in terms of density of growth and quality of synthesized nanotubes. These approaches include thermal treatment of silicon-germanium islands [3] and germanium Stranski-Krastanow quantum dots, germanium colloidal nanoparticles and germanium nanoparticles formed by ion implantation. Scanning electron microscopy measurements indicate that a good density of growth is achievable using this methodology. Raman measurements have identified the synthesized nanotubes as single walled and, in terms of graphitisation and structure, of a high quality. Extensive atomic force microscopy characterisation of the catalyst has been undertaken in order to ascertain the influence of morphology on the ability of germanium to catalyse CNT growth. Experimental evidence has shown that this technique offers a commercially scalable method of reliably growing metal-free CNTs for various applications, while opening the prospect of merging CNT devices with silicon electronics.

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Contributors

Author: C.H. de Groot

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