Fabrication of 3D Nanocarbon Structure for Potential Sensor Applications

Abstract

An all-carbon 3D nanocarbon structure has been designed and fabricated using carbon nanotubes (CNT) grown on multi-layer graphene (MLG). This work was motivated by the need of current integrated circuit (IC) technology to eventually replace copper (Cu) and tungsten (W) as interconnect materials. Such a structure can also potentially be part of a chemical or biological sensing system. Our experimental process consists of using a plasma-enhanced chemical vapor deposition (PECVD) process to grow CNT arrays directly on an MLG-covered silicon substrate after sputtering a thin nickel, iron, or cobalt (Co) catalyst film. The fabricated devices are evaluated and characterized through a combination of scanning electron microscopy and electrical measurements using a nanoprober. The PECVD process results in highly aligned but non-conductive CNT/Graphene structures due to damages in the graphene film during CNT growth. To mitigate this challenge, we successfully identified the source for graphene damage as the plasma in the CNT growth process and, as a result, replaced PECVD with a thermal CVD growth process. The resulting CNT/Graphene devices fabricated using Co as catalyst are conductive, with an estimated CNT-graphene contact resistance of 1.4 kΩ. Thus, we have taken the first step in demonstrating electrical conduction through an all-carbon, 3D nanostructure fabricated by growing CNTs directly on graphene. Further experimentation is currently underway to verify and improve upon our process, including in situ nanoprobing to fully characterize the electrical properties of these devices. In addition, we use a combination of transmission electron microscopy and electron energy loss spectroscopy to verify a homogenous interface between the CNT and MLG by demonstrating the continuation of C-C sp2 bonding. Independently, we are investigating the compatibility of our current process with other CNT growth catalysts. To achieve effective sensing, additional improvements are needed, such as vertical CNT alignment, high CNT areal density, and small average CNT diameter.