Abstract
Due to it’ s good conductivity and low-cost property, copper (Cu) is often used as interconnect and flexible transparent conductive film material with the introduction of nano-processing. Therefore, many studies try to analyze the properties of copper in nanoscale, such as nanowires (NWs). Twin is a common microstructure in metals. It has been demonstrated that nano-twinned copper have high mechanical strength, good conductivity, and moreover, superior electromigration resistance. In our previous study, we have successfully fabricated Cu NWs with high density of nanoscale traverse twinning structure by using pulsed electrodeposition at low temperature. The formation of nano-twinned structure can also improve the corrosion properties of Cu metallization by changing grain boundary structure. However, research report on the oxidation characteristics of nanotwinned Cu NWs is limited. Copper is prone to oxidation in nanoscale because of high surface-to-volume ratio, some researches showed that Cu-Ni NWs with core-shell structure that was prepared by coating a thin Ni layer on Cu NWs using chemical reduction method possesses good oxidation resistance. Nevertheless, these treatment were mostly done by using highly toxic reducing agent. In this study, high aspect-ratio nano-twinned Cu NWs were prepared by pulsed current (PC) electroplating, and Cu-Ni core-shell NWs were successfully prepared by the low-toxicity reducing agent, sodium borohydride. Time-and-temperature dependence of electrical resistivity for single Cu and Cu-Ni NWs prepared by micro-fabrication process has been investigated. The bamboo-like twinning structure and core-shell structure of Cu-Ni NWs have been examined by transmission electron microscopy (TEM) and UV-visible/TEM Energy Disperse X-ray analysis. According to four-probe I-V electrical measurement, the resistivity of Cu NWs with nanotwins remained almost constant after exposed in ambient air for one month, while the resistivity of Cu-Ni core-shell NWs also kept unchanged after hundreds hours of thermal aging, revealing good chemical stability.