Carbon nanotube-copper (CNT-Cu) composite with higher current-carrying capacity than copper
Copper and gold wires have been used to supply power to electronic devices which are widely used in society. The material and cross section of a wire are factors that determine the amount of current which can pass through the wire. The shrinking volume of electronic devices has resulted in reduction in the size of wiring within these devices. This limits the amount of current that can pass through the wiring.
Utilizing organic and aqueous electroplating of copper ions, copper and single wall CNTs synthesized using the Super Growth method were made into a composite (CNT-Cu composite) for wiring. This composite is light and exhibits unprecedentedly high electrical conductivity and ampacity. In addition, the composite retains high electrical conductivity at high temperatures. Thus, this material is expected to be a wiring material in miniaturized and high-performance electronic devices.
This study was conducted as a project, the "Development of innovative carbon nanotube composite materials for a low carbon emission society" (FY2010 – 2014, Project Leader: Motoo Yumura, AIST) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).
Details of this study have been published in a British scientific journal, Nature Communications, on July 23, 2013.
Electronic devices have been undergoing progressive miniaturization to provide increased portability and enhanced functionality for applications in all scenes of society.
AIST participates in TASC and has conducted application development of single wall CNTs synthesized by the Super-Growth method with higher specific surface area than other single wall CNTs in the "Development of innovative carbon nanotube composite materials for a low carbon emission society" project (FY2010 – 2014) of NEDO. AIST has developed a conductive rubber material in an AIST-TASC joint project that aims to promote integrated materials of single wall CNTs and existing materials and their practical applications.
In the present study, the researchers have developed a composite material using CNTs, a type of carbon-based material, with high ampacity and copper, a widely used wiring material, with high electrical conductivity.
The CNT-Cu composite is fabricated by electroplating of copper. The challenge in achieving the uniform CNT-Cu composite is to efficiently penetrate and uniformly fill copper into the matrix of CNTs. Conventional aqueous electroplating of copper fails to achieve this due to the hydrophobic nature of CNTs. Furthermore, electroplating of copper using an organic solution at high current density (50-100 mA/cm2) also fails to fill copper, with preferential copper deposition on the surface of the CNT matrix. In this study, the researchers fabricated the composite material by electroplating using an organic solution of copper and subsequent aqueous electroplating.
Vertically aligned super-growth single wall CNTs are made into a horizontally aligned CNT matrix. The next step constituted the uniform deposition of copper seeds into the CNT matrix by filling the matrix with an organic solution of copper and slow electroplating at low current density (1-5 mA/cm2). As the deposited seeds are copper and copper oxide, the matrix was washed and then the copper oxide seeds are reduced to form copper seeds by heating in a hydrogen atmosphere. Next, the matrix was filled with cupper by the conventional aqueous electroplating. After this electroplating, the matrix was washed and heated in a hydrogen atmosphere. Thus, the uniform CNT-Cu composite was fabricated by forming copper seeds in the CNT matrix by slow electroplating using an organic solvent, which has an affinity with CNTs, and subsequent electroplating using aqueous solution, which has an affinity with copper (Fig. 1).
Further, the room temperature electrical conductivity of the CNT-Cu composite is 4.7 x 105 S/cm and is comparable with pure copper (5.8 x 105 S/cm). The decrease in electrical conductivity of the CNT-Cu composite was less than copper and the conductivity exceeded that of copper above 80 °C and was double it at 227 °C (Fig. 3).
Provided by Advanced Industrial Science and Technology