IBM reduces contacts for carbon nanotube transistor

IBM has reduced the contacts for a carbon nanotube transistor to less than 10nm without compromising the transistor’s performance. The scientists managed to keep the resistance low with their process, despite the reduction.

Silicon is reaching its limits, but before carbon nanotubes can be used as an alternative, many hurdles have to be overcome, says Shu-Jen Han of IBM Research. One of those obstacles was being able to shrink the two contacts on either side of the channel. The resistance increases on such a small scale and the effective inflow simply stops if the resistance at the contacts is too high.

The researchers have now succeeded in reducing the contacts to 9nm, without increasing the electrical resistance due to the reduction. To do this, they ‘welded’ the metal molybdenum at the ends of the nanotubes and the high temperature converted it into carbide. Previously, the scientists could only place a metal directly on the tubes, which had a negative influence on the resistance.

Although IBM calls it a big step towards deploying carbon nanotubes for transistors, many problems remain to be overcome. For example, they have only demonstrated the usefulness of the current process for transistors with p-channels and p-type contacts; they expect to encounter difficulties in n-type contacts.

There are also many hurdles to scaling carbon nanotubes to wafers. IBM has already managed to self-assemble carbon nanotubes to molecules on a wafer, but the ultimate goal is to increase the density and apply it to an entire wafer.

IBM’s research is published in the October 2 issue of Science under the heading End-bonded contacts for carbon nanotube transistors with low, size-independent resistance.