2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Directed Growth of Carbon Nanotubes Utilizing Plasma Induced Surface Charging Voltage

J.B.K. Law, C.K. Koo and J.T.L. Thong
National University of Singapore, SG

carbon nanotubes, synthesis, directed growth, lateral, electric field, assembly, plasma induced surface charging

In this work, we present a method for directed lateral growth of CNTs between electrodes on a substrate during an in-situ CNT growth process, by utilizing plasma induced charging inherent in a Radio Frequency (RF) plasma process to achieve self-generated electric fields between adjacent electrodes. A Silicon-On-Insulator (SOI) die was fabricated to form a pair of p++ Si electrodes with lithographically patterned iron (Fe) catalyst islands on the edges of the electrodes. One electrode was electrically connected to the substrate by a Platinum (Pt) via while the adjacent electrode is electrically isolated. A control experiment with a pair of electrodes electrically connected to the substrate by Pt vias was fabricated on the same die. Figure 1 illustrates the cross-sectional view of the die. CNT growth was performed using Radio Frequency–Plasma Enhanced Chemical Vapor Deposition (RF-PECVD). The isolated electrode charged to a DC voltage, a phenomenon known as plasma induced charging. A self-generated electric field is thus established during the growth between the isolated electrode with respect to the adjacent electrode to direct the growth of CNTs. The magnitude of this charging voltage during plasma processing was also experimentally measured. After growth, SEM images shows aligned and straight growth of CNTs in the direction of the electric field between the isolated electrode and the adjacent electrode connected to the substrate (Figure 2) whereas randomly oriented and curly CNTs were grown between the pair of grounded electrodes on the same die. The present work thus provides an alternative method for directed growth of CNTs utilizing electric-field assisted assembly. Conventional methods using in-situ growth assembly or post-growth assembly suffers from limitations such as the need for an externally applied electric field and subsequently the need for large size electrode pads and non-scalability in manufacturing. In contrast, the present technique does not require large size contact pads on the substrate. If a network of CNT assembly is required, elaborate and messy external contacts and electrical feed-throughs to the process chamber are not required since there is no need to apply any external biasing. More importantly, conventional scalable semiconductor processes can be utilized in this technique, making it a viable technique for large-scale integration.

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