One of the main limiting factors for the integration of carbon nanotubes with existing microelectronics is the temperature needed to grow the nanotubes. In thermal chemical vapor deposition, CVD, temperatures of about 700-900 C are typically used. If nanotubes are to fulfil their promise in real applications it is essential to reduce the sample temperature during growth to values compatible with CMOS processing.
Here we present a method for growing single- and multi-walled nanotubes on-chip while keeping the mean sample temperature at 60 C. By lithographic patterning we create electrode structures where localised ohmic heating at the catalyst site allows controlled growth of nanotubes on metal electrodes. Heating of the catalyst site is extemely local with a temperature gradient close to the hot-zone on the order of 100 C/micrometer.
We study the effects of different carbon precursors as well as the possibilities of directing the nanotubes while growing using electric fields. The growth is very efficient using acetylene as carbon precursor but we seem to have better control of the directionality of ethylene tubes.
The effect of growth time as well as pressure is investigated.
Keeping the sample temperature low during growth benefits the integration of carbon nanotubes with CMOS technology and also permits using temperature sensitive materials as building blocks for nanoelectromechanical or optical structures on chip. This resistive growth method also opens up the possibility of sequential growth, with potentially large impact on how future nanotube growth on chip will be performed.
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