Synthesis of Controllably Grown Carbon Nanotubes Interconnects
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1018-EE05-02
Synthesis of Controllably Grown Carbon Nanotubes Interconnects Seon Woo Lee1, David Katz1, Avi Kornblit2, Daniel Lopez2, and Haim Grebel1 1 Electrical and Computer Engineering, Electronic Imaging Center at New Jersey Institute of Technology, Newark, NJ, 07102 2 New Jersey Nanotechnology Consortium (NJNC), Lucent Technologies Bell Labs, Murray Hill, NJ, 07974
ABSTRACT Carbon nanotube (CNT) intra-connects (bridges spanning across in-plane electrodes) were fabricated. We have assessed several growth methods for these intra-connects: Plasma Enhanced Chemical Vapor Deposition with CO precursor (PECVD/CO), CVD/ethanol and pyrolitic CVD/CO. PECVD/CO has been used with a mixture of CO/H2 at relatively low temperatures. Its yield was relatively low and quality of the intra-connects was not to par. CVD/ethanol resulted in many more multi-wall carbon nanotubes (MWCNT) than single-wall carbon nanotube (SWCNT) intra-connects. CVD/CO was the most effective and simplest way to grow CNT intra-connects among the three methods, yielding well-aligned and straight SWCNT bridges. INTRODUCTION Carbon nanotubes (CNT) have been attracted extensive attention in recent years due to their unique electrical, optical and mechanical properties [1-3]. CNT interconnects may find applications in nano-electronic circuits and devices [4]. Connecting two electrodes by a single channel may be made within the chip plane (intra-connect) and across layers (inter-connect). Here we are focusing on intra-connects for CNT based elements such as, field effect transistors (FET). With single-electron, optoelectronic devices in mind, intra-connecting metal electrodes by carbon nanotube (CNT) at precise locations is of great challenge. So far, most fabrication methods were based on first dispersing CNT on a substrate and then following with postprocessed contacts [5-7]. Growth between periodic and extended electrode grids and between pre-determined pads was also attempted at a limited yield [8-10]. Here, we demonstrate CNT intra-connects between pre-fabricated and addressable two sharp metal catalytic tips, taking advantage of the tip dimension and the thermal distribution at the tip vicinity: we grew bridges between precise locations at a yield approaching 30% depending on the electrode construction (sampling pool was more than 150 electrode-pairs). EXPERIMENT We combined state-of-the-art optical lithography with chemical vapor deposition (CVD) in the range of 600-900 oC to initiate growth of tubes between two sub-micron catalytic metal tips. The metal tips were composed of Co (~30 nm) on top of Ti layer (~30 nm) and were deposited on Si wafers (Figure 1(a)). This well-defined catalytic pattern was introduced into a quartz tube, where
we used PECVD with CO/H2 mixture, CVD with ethanol and pyrolitic CVD with CO. PECVD has been used at a relatively low temperature range (600-800 oC). We used a Radio-Frequency (RF) source at 13.6 MHz with inductive Ni or W wire antennas. In the case of ordinary CVD process, the temperatures range was 700-800 oC in A
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