Graphitic nanojoints yield better connection to metal junctions

November 23, 2012 // By Julien Happich
Researchers at the Georgia Institute of Technology have developed graphitic nanojoints on both ends of multi-walled carbon nanotubes, which yielded a 10-fold decrease in resistivity in connection to metal junctions.

Based on electron beam-induced deposition (EBID), the technique could facilitate the integration of carbon nanotubes as interconnects in next-generation integrated circuits that use both silicon and carbon components.

"For the first time, we have established connections to multiple shells of carbon nanotubes with a technique that is amenable to integration with conventional integrated circuit microfabrication processes," said Andrei Fedorov, a professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. "Connecting to multiple shells allows us to dramatically reduce the resistance and move to the next level of device performance."

In developing the new technique, the researchers relied on modeling to guide their process parameters. To make it scalable for manufacturing, they also worked toward technologies for isolating and aligning individual carbon nanotubes between the metal terminals on a silicon substrate, and for examining the properties of the resulting structures. The researchers believe the technique could also be used to connect multi-layered graphene to metal contacts, though their published research has so far focused on carbon nanotubes.

The low-temperature EBID process takes place in a scanning electron microscope (SEM) system modified for material deposition. The SEM's vacuum chamber is altered to introduce precursors of the materials that researchers would like to deposit. The electron gun normally used for imaging of nanostructures is instead used to generate low energy secondary electrons when the high energy primary electrons impinge on the substrate at carefully chosen locations. When the secondary electrons interact with hydrocarbon precursor molecules introduced into the SEM chamber, carbon is deposited in desired locations.

Unique to the EBID process, the deposited carbon makes a strong, chemically-bonded connection to the ends of the carbon nanotubes, unlike the weakly-coupled physical interface made in traditional techniques based on metal evaporation. Prior to deposition, the ends of the nanotubes are opened using an etching process, so the deposited carbon grows into the open end of the nanotube to electronically connect multiple