Researchers in Sweden have demonstrated carbon nanotube interconnect between stacked chips.
Industry so far has been using mostly copper for through-silicon vias (TSVs).
"Potentially, carbon nanotubes have much better properties than copper, both in terms of thermal and electrical conductivity", said Chalmers University professor Kjell Jeppsson. "Carbon nanotubes are also better suited for use with silicon from a purely mechanical point of view. They expand about the same amount as the surrounding silicon while copper expands more, which results in mechanical tension that can cause the components to break."
Both stacked chips and chip-to-package connections have been made with carbon TSVs by the team.
Adhesive is used to hold the die together.
PhD student Teng Wang developed the technique that fills vias with thousands of nanotubes.
"One difficulty involves producing carbon nanotubes with perfect properties and with the length we need to go through the chip," said Wang. "We have produced tubes that are 200µm long, which can be compared to the diameter which is only 10nm. Their properties, however, are not yet perfect."
One problem is that in-situ nanotube growth requires temperatures higher than silicon circuits can stand.
There are papers on the work in Small and Advanced Materials:
Carbon-nanotube through-silicon via interconnects for three-dimensional integration and
Ultrafast transfer of metal-enhanced carbon nanotubes at low temperature for large-scale electronics Assembly.