In this paper, nano-scale bonding processes of carbon nano tube (CNT)-CNT and CNT-metallic pad by using a scanning tunneling microscope (STM) tip and a development of the electrical contacts were reported. Recently, CNT is expected to be applicable for various types of nano-scale devices because of the scale of the size. Moreover, considering an ability of the carrier transport, it could be used as a wiring material in nano-scale circuits, if the handling technique is established enough. Because it is predicted the carrier in CNT would transport in a ballistic regime, if there were no defect on it . Moreover, it should be remarkable that a maximum current density of CNT is more than 2 orders superior to a conventional wiring material in a LSI such as Cu or Al without an electrical migration. However, because of the difficulty of the handling, it is difficult to realize such a CNT wiring system. If we could use the system like a wire bonding in semiconductor technology, it would be convenient and show a high performance for a bonding in nano-scale regions. In order to realize such a system, it is necessary to put CNT at an aimed area. Nowadays, a development of nano-manipulation techniques using a small probe is getting developed to manipulate an individual CNT. However, it is also important to make a bonding CNT on metallic electrodes to have a good ohmic and mechanical contact. As for such a possible method, we propose a nano-scale bonding process by a voltage pulse applied on a STM tip. The advantageous is that we can deposit nano-scale metallic clusters at any position on a metallic pad and also cover CNT by them,
which would bring a good contact between CNT and a pad.
For all of the bonding process, a SEM/ STM combined system was used. Watching the SEM image, the tip was approached just on CNT within an accuracy of 100nm. The figure is a demonstration for CNT-CNT bonding on a gold substrate, which are connected by a 50nm scale gold dot on the cross point of two CNT by applying a voltage pulse of 10V peak and 50µs duration on a gold-coated tip. Moreover, we could obtain a good improvement of electric contacts between CNT and metallic (titanium) pads by depositing titanium clusters from a tip by similar process. In this case, the two terminal I-V characteristic of CNT was clearly improved from nonlinear to linear, where the conductance changed from 4.8µS to 560µS at 2.5V after the process. These bonding processes are using differences of critical fields for field evaporation in a STM regime . It would be possible to deposit metal clusters onto CNT without introducing a serious damage on it, if we choose a proper voltage. Because the critical voltage value for gold and titanium are 8.5V and 7.0V, respectively, however that for carbon is more than 20V.