In-Coated Carbon Nanotubes for Flexible Interconnects

This work explores a method to construct metal-coated carbon nanotube (CNT) structures, which are potential candidates for interconnects, transmission lines and contact structures. This simple method is suitable to many applications including flexible substrates. In this work, electroplating is used to coat a carbon nanotube surface with Indium. CNT films are prepared using drop casting method on different substrates: Ni coated silicon wafer, copy paper and photo paper. The CNT dispersion used for this work is prepared using sonication and centrifugation with a surfactant. The resulting dispersion has 0.8 wt. % of multi-walled CNTs and 0.5 wt. % of sodium dodecyl sulfate (SDS) in DI water. This dispersion is modified to reduce resistivity by adding either silver nanoparticle powder or silver ink. Electroplating is done at room temperature with a current density of 0.02 A/cm2. This work addresses two issues about electroplating on CNT: low electrical conductivity of CNT film and low CNT adhesion to substrate. A CNT film on a Ni surface displays poor adhesion; the film peels off easily during ultrasonication and electroplating. After thermal annealing or microwave treatment, adhesion between the CNT film and Ni is greatly enhanced such that no CNT film peel-off is observed during electroplating. A CNT film on paper has a high sheet resistance. As a result, Indium is only plated on the CNT film near the attached electrode. To reduce the film sheet resistance, the CNT solution is modified by adding silver nanoparticle powder or silver ink. Ethanol rinsing is also performed on the CNT film surface to wash away surfactant and further reduce sheet resistance. On-going work involves ink-jet printing of CNT solutions onto flexible substrates. Indium, as an example metallization, will be plated on these ink-jet printing defined transmission lines and interconnects patterns. Performance of these structures will be presented.