We have developed carbon nanotube (CNT) vias consisting of about 1000 tubes using thermal chemical vapor deposition (CVD) at a growth temperature of 450°C with cobalt catalysts, titanium carbide ohmic contacts, and tantalum barrier layers on copper wiring. The lowest resistance obtained was about 5 Ω/via. The total resistance of the CNT via was three orders of magnitude lower than that of one CNT, indicating that the current flows in parallel through about 1000 tubes. No degradation was observed for 100 hours at via current densities of 2×106 A/cm2, which is favorably compared with Cu vias.

A novel carbon composite structure consisiting of graphene multi-layers and aligned multi-walled carbon nanotubes (MWNTs) has been discovered. The composite structure, which was synthesized by chemical vapor deposition, has graphene multi-layers combined with the upper ends of vertically aligned MWNTs on a substrate. This microscopically-combined structure has been confirmed by transmission electron microscopy. The substrate with the new structure looks gray and shiny, which is completely different from the appearance of a substrate with the usual vertically-aligned MWNTs. The new composite structure is expected to have excellent electrical and thermal properties, and therefore is likely to find many applications in electronics.

Thickness-controlled growth of few-layer and multi-layer graphene was performed at 650 °C by thermal chemical vapor deposition, and top-gated field effect transistors (FETs) were fabricated directly on a large SiO2/Si substrate without graphene-transfer processes. Graphene was synthesized on patterned Fe films. The iron was subsequently etched after both ends of the graphene were fixed by source and drain electrodes, leaving the graphene channels bridging the electrodes all over the substrate. Top-gated FETs were then made after covering the channels with HfO2. The fabricated devices exhibit ambipolar behavior and can sustain a high-density current. The growth mechanism of graphene was also investigated.

We propose a new approach to fabricating carbon nanotube (CNT) via interconnects for future LSIs, which uses preformed catalyst nanoparticles to grow the CNTs. A newly designed impactor provided size‐classified catalyst particles. For the new approach, we employ a TiN contact layer which is more resistant to oxidation and enables us to form a lower resistance ohmic contact between CNTs and wiring layers. The resultant CNT–via resistance was 0.59 Ω for 2‐µm vias, which is the smallest ever reported. We also study the CNT nucleation process using molecular dynamics and discuss how to remove amorphous carbon from the nucleation process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)