AIST Uses CNTs for TSVs by Improving Heat Conductivity

Dec 19, 2012
Masahide Kimura, Nikkei Electronics
Heat is released from a chip by using TSVs made of CNTs.
Heat is released from a chip by using TSVs made of CNTs.
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Japan's National Institute of Advanced Industrial Science and Technology (AIST) made an announcement about the development of a thermal via using carbon nanotubes (CNTs) at IEDM 2012 (lecture number 33.5).

The thermal conductivity of CNTs is 3,000W/mK, which is about ten times higher than that of copper (Cu) (about 400W/mK). Also, the effect of the stress that CNTs impose on silicon (Si) due to thermal expansion is smaller than in the case of Cu. Therefore, AIST has been developing a technology for forming through-silicon-vias (TSVs) made of CNTs on a semiconductor chip and using them as thermal paths.

However, it was difficult to improve thermal conductivity because of the low density of CNTs made with chemical vapor deposition (CVD) technology.

This time, AIST increased the thickness of cobalt (Co) catalyst to about 1.5nm and used a film-forming method called "STEP," which grows graphene at a low temperature and, then, raises the temperature while controlling the temperature profile. As a result, it succeeded in forming high-density CNTs and improving thermal conductivity by 10-100 times to 260W/mK.

At this point, the thermal conductivity has not yet reached that of Cu. And AIST plans to realize a high thermal conductivity that CNTs originally have by making further improvements.