New technique enables smaller chips

The research has been undertaken by Professor John Robertson and Santiago Esconjauregui at the University of Cambridge Engineering Department. Traditionally, integrated circuits are constructed in layers, each with a number of separate electrical components connected by tiny copper wires, within and between the layers. As ICs become smaller, so must the copper connectors, resulting in the electrical current density within the copper becoming proportionally higher. Eventually no more current can be passed through the connector. Prof Robertson says his team has devised a method using carbon nanotubes instead of copper connectors in ICs, enabling smaller circuits to be built and reducing the size of electronics even further. The carbon nanotubes consist of atoms arranged hexagonally and layered in sheets which are then rolled up to form minute tubes. The diameter of the tubes is equivalent to just a few carbon atoms. Individual carbon nanotubes can support extremely high electrical current densities, but need to be grown in dense bundles directly onto the substrate. This is normally achieved by depositing a thin film of a catalyst, such as iron, onto the substrate and changing the properties of the catalyst through the use of heat. This process – annealing - produces a series of nanoparticles which are the basis for the growth of each nanotube. This method does produce nanotube bundles, but they have limited spatial density, and carry insufficient electrical current for microchip purposes. Prof Robertson and his colleagues have devised a method for growing nanotube bundles through multiple deposition and annealing steps, resulting in successive increases in nanoparticle density. The resulting bundles have a density that is five times greater than the closest available technology, with further density increases possible in the future.