Effects of local Joule heating on the reduction of contact resistance between carbon nanotubes and metal electrodes

We report here a practical application of known local Joule heating processes to reduce the contact resistance between carbon nanotubes and metallic electrical contacts. The results presented in this study were obtained from a series of systematic Joule heating experiments on 289 single-walled carbon nanotubes (SWCNTs) and 107 multiwalled carbon nanotubes (MWCNTs). Our experimental results demonstrate that the Joule heating process decreases the contact resistances of SWCNTs and MWCNTs to 70.4% and 77.9% of their initial resistances, respectively. The I-V characteristics of metallic nanotubes become more linear and eventually become independent of the gate voltages (Vgs). For semiconducting nanotubes, the contact resistance has a similar decreasing tendency but the dependency of source-drain current (Ids) on Vgs does not change with the Joule heating process. This suggests that the reduction of the contact resistance and the decrease of the transport potential barrier are largely attributed to the thermal-energy-induced desorption of adsorbates such as water and oxygen molecules from the nanotube surface and the interface region, as well as thermal-energy-enhanced bonding between the nanotubes and electrode surfaces. In comparison to several other methods including rapid thermal annealing, e-beam lithography patterning of the top metal layer, and focused ion beam induced metal deposition of the top layer, the Joule heating process not only effectively reduces the contact resistance but also simultaneously measures the resistance and monitors the change in the transport potential barrier at the interface region