Hybrid Cu-carbon nanotube (CNT) conductors provide high electrical conductivities, while benefiting from the low temperature coefficient of resistance for CNTs. However, the poor interaction between Cu and CNTs requires a method of interfacing the components to improve the connectivity of the Cu-CNT conductor while preserving the electrical properties. Herein, Ti and Ni were evaluated as interfacial metals by thermally evaporating 10 nm layers onto a CNT conductor to assess the nanoscale morphology and impact on temperature dependent electrical properties. SEM analysis shows Ni deposits onto the CNT surface as a continuous layer in the form of discrete nanoscale crystallites. In contrast, Ti deposits a uniform layer along the surface of the CNT network. The Ni crystallites coalesce from the initially continuous layer upon exposure to temperatures up to 400 °C, while Ti is shown to remain as a stable uniform coating on the CNTs over such temperatures. Subsequent deposition of a 100 nm Cu layer onto CNT, Ti-CNT, and Ni-CNT conductors was performed to measure electrical stability with increasing annealing temperature. The 100 nm Cu layer forms gaps as it delaminates from the CNTs after exposure to 400 °C in a H2/Ar anneal when no adhesion metal is present, and the resistance per length (R/L) increases by 40%. The gaps formed in the Cu layer by the 400 °C anneal expose underlying CNTs, indicating poor surface interaction. The Cu-Ni-CNT conductor maintains Cu layer integrity from the adhesion metal, but exhibits a 125% increase in R/L for similar annealing conditions. In comparison, Ti sustains favorable interaction for the metal layers on CNTs, and achieves a 12% reduction in R/L after exposure to 400 °C. Temperature dependent electrical measurements performed under vacuum confirm the permanent change in electrical properties at elevated temperature for the hybrid conductors with an adhesion metal, demonstrating the increase in R/L for the Cu-Ni-CNTs and a decrease in R/L for Cu-Ti-CNT conductors. Thus, Ti emerges as an effective adhesion metal for use in metal-CNT conductor operation at elevated temperatures, demonstrating sustained adhesion up to 400 °C, and improvement in electrical properties for Cu-Ti-CNT conductors. Transitioning to scalable systems for integrated CNT conductors, a chemical vapor deposition (CVD) technique will be investigated as a delivery route for improved penetration of Ti into the CNT network.
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