However, with electrical gadgets and devices getting increasingly smaller and functionally more powerful, the current density flowing through the copper and gold conductors in these devices – which supply power to transistors, switches and memory – has been exponentially increasing.
"Currently, technologically, we are at the limits of what copper and gold can deliver in terms of current density and electrical conductivity," Chandramouli Subramaniam, a researcher at the Super Growth CNT - Nanotube Research Center at AIST in Japan, tells Nanowerk. "Therefore, electrical conductors with higher current density tolerance (or current carrying capacity) are in huge demand. Our recent research was motivated to address this demand."
Subramaniam and his colleagues, together with collaborators from the Technology Research Association for Single Wall Carbon Nanotubes, have now developed a carbon nanotube-copper (CNT-Cu) nanocomposite material that overcomes the mutual exclusivity of high ampacity and high conductivity – the former requires a strongly bonded system, whereas the latter requires the free electrons from a weakly bonded system – by effectively combining the strengths of copper (high electrical conductivity) and CNTs (high current density tolerance) into one integrated composite material.
"We discovered that the presence of carbon nanotubes leads to the suppression of atomic electromigration of copper," explains Subramaniam. "Suppressing the mass-diffusion of copper – under the influence of electric field – provides our CNT-Cu composite material with a high degree of tolerance to current density. Thus, CNT-Cu is able to withstand and transport over 100 times higher current density compared to metals such as copper, gold and silver."
Importantly, the researchers were able to achieve this high current density tolerance without sacrificing the electrical conductivity of the material, which is similar to that of pure copper.
"This is the first such material, to the best of my knowledge, that can have high electrical conductivity and high current density tolerance," Subramaniam points out. "I consider this to be a huge advancement in the field of electrical power transmission, ranging from interconnects and vias – in integrated chips and microelectronic devices – to high power transmission."
To fabricate their CNT–Cu composite, the team developed a unique fabrication process. In contrast to conventional approaches that use CNT–Cu ion dispersions, they electrodeposited copper into the pores of premade, macroscopic CNT structures such as buckypaper and closely packed CNT forests. The result is a composite where the CNT cover the surfaces and grain boundaries of polycrystalline copper.
This CNT-Cu material with high current carrying capacity is likely to find applications in all areas where high ampacity, low density electrical conductors are required.