Nanotubes with chips

Scientists from Infineon Technologies in Munich are claiming to have made a crucial breakthrough in the field of carbon nanotube research.

Scientists from Infineon Technologies in Munich are claiming to have made a crucial breakthrough in the field of carbon nanotube (CNT) research.

By modifying a tried-and-tested microelectronics process, the scientists have grown CNTs in a highly parallel batch process at predefined locations on 6′ silicon wafers. The properties of these CNTs, which include very high current densities and thermal conductivities almost twice that of diamond, can now be used for the first time in the development of ICs.

‘The present results are completely reproducible and the structures grow at the predefined locations with sufficient homogeneity over the whole wafer,’ said Dr. Sönke Mehrgardt, member of the board and chief technology officer of Infineon Technologies. ‘The growth process lasts only a few minutes. These are optimum prerequisites for integration in semiconductor production line processes.’

The first possible use of the CNTs is in building vias – the contact bridges between two metal layers in ICs. Due to high current densities and associated heating, conventional vias tend to distort and impair the operational ability of ICs. CNT vias, on the other hand, can handle considerably larger current densities and also possess a much higher mechanical stability.

‘With this discovery we can consider replacing all of the metal conductors in the chips with CNTs,’ said Dr. Franz Kreupl. This would ultimately lead to a considerable increase of the on-chip clock rate.

Replacement of the conductors with CNTs is only one possible application, however. One other characteristic of the tubes is that it is possible to make them semiconducting and also to dope them. That means active switching elements, such as field-effect transistors, can also be made. The energy gap of the semiconducting tubes can be controlled by defining the diameter.

Researchers at Infineon are also working on growing such semiconducting CNTs on wafers using the same catalytic deposition method.

‘The whole topic has a promising future. It is very possible that this technology could completely replace silicon-based semiconductor technology,’ claims team leader Dr. Hönlein. In this case, the relatively expensive silicon could be replaced by glass. But that is not enough. The Infineon researchers are already playing with ideas in which CNTs are used to extend current planar microelectronics into a proper 3-D technology.

Editor’s note: Carbon nanotubes belong to the Fullerene family and stand alongside graphite and diamond as the third form of carbon. A Fullerene is a cluster with a closed polyhedral structure (a type of nano-football) composed of an even number, mostly 60 or 70, carbon atoms. CNTs, on the other hand, are not round, but long and are tiny, defect-free tubes with extremely high length to diameter ratios. The tube diameter can be varied between 0.4 nm and 100nm whilst the length can reach 1 mm at present.

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