Graphene Replaced with Copper

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Graphene replaced with copper
Graphene nanoribbons have a current-carrying capacity two orders of magnitude higher than copper Recent research into the properties of graphene nanoribbons provides two new reasons for using the material for interconnects in future computer chips. In widths as narrow as 16 nm, graphene has a current-carrying capacity approximately a thousand times greater than copper while providing improved thermal conductivity. The current-carrying and heat-transfer measurements were reported by a team of researchers from the Georgia Institute of Technology (Atlanta, GA). The same team had previously reported measurements of resistivity in graphene that suggest the material’s conductance would outperform that of copper in future generations of nanometer-scale interconnects. The graphene nanoribbons have a current-carrying capacity two orders of magnitude higher than copper at these size scales, according to Raghunath Murali, a senior research engineer at Georgia Tech. {draw:frame}

Composed of thin layers of graphite, graphene has been studied by the Georgia Tech team as a potential replacement for copper in on-chip interconnects wires. The graphene nanoribbons have a current-carrying capacity of more than 108 A/cm2, which makes them very robust in resisting electromigration and should greatly improve chip reliability. This electromigration phenomenon causes transport of material, especially at high-current density and leads to a break in the wire and, consequently, chip failure. The research team also discovered that the graphene nanoribbons also have excellent thermal conductivity properties and can conduct heat away from devices. They found that graphene nanoribbons have a thermal conductivity of more than 1,000 W/m Kelvin for structures less than 20 nm wide. This will help the interconnects serve as heat spreaders in future generations of integrated circuits, according to Murali. They used electron beam lithography to construct four electrode contacts, then used lithography to fabricate devices consisting of parallel nanoribbons of widths ranging between 16 and 52 nm and lengths of between 0.2 and 1 µm. The breakdown current density of the nanoribbons was then studied by slowly applying an increasing amount of current to the electrodes on either side of the parallel nanoribbons. A drop in current flow indicated the breakdown of one or more of the nanoribbons. In the study of 21 test devices, the researchers found that the breakdown current density of graphene nanoribbons has a reciprocal relationship to the resistivity. Because graphene can be patterned using conventional chip-making processes, manufacturers could make the transition from copper to graphene without a drastic change in chip fabrication. The data they developed so far look very promising for using this material as the basis for future on-chip interconnects. Visit to view a video explaining graphene’s thermal-conductivity capabilities. Though one of graphene’s key properties is reported to be ballistic transport—meaning electrons can flow through it without resistance—the material’s actual conductance is limited by factors that include scattering from impurities, line-edge roughness and from substrate phonons—vibrations in the substrate lattice. Use of graphene interconnects could help facilitate continuing increases in integrated circuit performance once features sizes drop to approximately 20 nanometers, which could happen in the next five years, researchers said. At that scale, the increased resistance of copper interconnects could offset performance increases, meaning that without other improvements, higher density wouldn’t produce faster integrated circuits. This is not a roadblock to achieving scaling from one generation to the next, but it is a roadblock to achieving increased performance. Dimensional scaling could continue, but because we would be giving up so much in terms of...
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