Carbon nanotubes in nanopackaging applications

CNTs are recently discovered materials made by rolled-up sheets of graphene. They may be made either by a single shell [single-walled CNT (SWCNT) with radius ranging from 0.7 to 3-4 nm] or several nested shells [multiwalled CNT (MWCNT) with outer radius typically of the order of some tens of nanometers]. The length of a nanotube may reach the order of millimeters, and hence, this nanostructured material exhibits an excellent form factor, able to comply with the ultrafine pitches required in nanopackaging. CNT (carbon nanotubes) to be used for vertical vias or interconnects for packaging applications, very high-density SWCNT bundles must be demonstrated. When using MWCNT bundles instead, the achieved density comes from a compromise between the CNT radius and its shell number. The fabrication process must provide low contact resistance, good direction control, and compatibility with CMOS technology. The road for CNTs to replace copper in chip packaging is still long, but the gap between theoretical predictions and practical applications is reducing faster and faster.