Carbon Nanotubes Array as Template for Metallic Interconnections

Modern integrated circuits are mainly speed-limited by their interconnects and presently many new materials and systems are being developed to address the needs for higher temperature operation and longer working life. Conventional materials, like Cu, are limited in carrying high current densities by metal atoms electromigration that leads to structural failures and reduction of device reliability. Moreover thermal expansion/contraction processes can cause shear strain at the joints (end bonding). In the last decade significant advances in material performances have been made by using carbon nanotubes, that, owing to their extraordinary electrical, mechanical an thermal properties, may provide solutions for interconnects and chip cooling in future IC technologies [1]. On the other hand, nanostructured Cu and Ni have been proposed as reliable primary interconnection materials in view of the enhanced properties of mechanical resistance exhibited by these metals at the nanoscale [2]. In order to comply with these indications, practical solutions must be found for the fabrication of well defined architectures assembled by nanosized Cu or Ni deposits. Because the electrical properties of the Ni decorated SWCNT are expected to depend on the concentration of Ni nanoparticles, we started to deposit low concentration of about 50 nm Ni nanoparticles on the surface of SWCNT fibres with diameter of 100 μm [3]. Resistance vs. temperature and current voltage measurements show that the metallic properties of the fibres are enhanced by this interaction. Moreover, magnetoresistance measurements indicate this effect can be attributed to the delocalization of the electron wavefunction. All these results gave a strong effort in the use of SWCNT as good templates for interconnection in integrate circuits. Depositing Ni nanoparticles on arrays consisting of aligned SWCNT bundles [4,5], experimental data show a complete transition to metallic behaviour starting from the semiconducting character of the bare SWCNT bundle array observed before the Ni deposition. Comparing the results obtained for the fibres and the bundle arrays covered by Ni nanoparticles with that obtained for the same samples before the Ni deposition, interesting indications on the influence of Ni on the transport mechanism inside the SWCNT are acquired.