Aug 17, 2012
CVD graphene nanoribbons make good interconnects
Nanoribbons obtained from graphene grown by chemical vapour deposition (CVD) could make ideal interconnects for nanoelectronic circuits. So say researchers at the University of Illinois in the US who have measured current densities in these materials of a record-breaking 2 × 109 A cm–2 on common silicon-oxide substrates.
Graphene – a 2D sheet of carbon just one atom thick – could be ideal for use in future electronics applications thanks to the fact that electrons whizz through the material at extremely high speeds. The material also conducts heat extremely well and can be transferred onto virtually any substrate.
Graphene nanoribbons (GNRs) could be ideal as interconnects and to make high-frequency transistors and sensors. Although researchers have already characterized nanoribbons made from graphene obtained by exfoliation (the now-famous “sticky tape” method), ribbons made from graphene produced by other methods, such as CVD, have been much less studied. Nanoribbons made from exfoliated graphene have very good electronic properties thanks to lack of bulk defects in these materials, but exfoliation cannot be used to produce large-area graphene samples suitable for real-world applications. CVD, on the other hand, is a cheap and easy way to make polycrystalline graphene films with grain sizes of micrometres or more.
Eric Pop and colleagues have now studied nanoscale GNRs (less than 800 nm long and less than 100 nm wide) obtained from CVD graphene. The researchers, who report their work in Nano Letters, have discovered that these ribbons have similar electronic properties to those made from graphene obtained by other processing methods, including exfoliation. The result proves that bulk defects and grain boundaries produced during CVD have little effect on the final electronic characteristics of CVD GNR interconnects, says Pop.
High current densities
“At high fields, we found some of the highest current densities (an important criteria for evaluating interconnect performance) ever recorded in either graphene or GNR interconnects of around 2 × 109 A cm–2,” he told nanotechweb.org. This value is nearly 1000 times higher than that of copper, widely used as an interconnect material in today’s silicon-based circuits.
The Illinois researchers obtained their results by measuring the current that flowed through GNRs arranged in a two-terminal configuration. They also compared their results with extensive simulations and showed that short interconnects can sink heat into their contacts and substrates. This advantage is what ultimately enables the high current densities, says Pop.
“We believe that our work is an important step towards understanding and making wafer-scale graphene interconnects in electronics,” explained Ashkan Behnam, the lead author of the study. “But we have also shown that controlling some of the fabrication parameters will continue to be important, for example, decreasing the edge roughness of such interconnects and improving their variability across a chip.”
The team revealed that it is already using such graphene interconnects within memory applications, where they serve as the “wiring” for data storage bits. “We are now focusing on further increasing the current densities through the interconnects by lowering their resistance,” said Pop. “One approach we are looking at is to control the edge roughness and doping levels in the nanoribbons.
About the author
Belle Dumé is contributing editor at nanotechweb.org.