Carbon Nanotube Growth for GHz Devices Shengdong Li 1 , Zhen Yu 1 , Goldie Gadde 1 , Peter J. Burke 1,2,† , W. C. Tang 1,2 1 Electrical Engineering and Computer Science, 2 Biomedical Engineering University of California, Irvine Irvine, CA 92697 Abstract— Horizontally oriented single walled carbon nan- otubes are grown with CVD between lithographically defined catalyst sites. Single walled carbon nanotubes up to 60 μm in length are grown using methane as the feedstock. The nanoparti- cle catalyst is deposited from a newly developed aqueous solution requiring only photoresist and optical lithography. Carbon nan- otube Y-junctions are also observed and characterized. I. I NTRODUCTION In this paper we describe the growth of carbon nanotubes for the development of GHz electronic devices. Recently one of us[1], [2] predicted that the inductance of a nanotube should be very large (∼10 nH/μm) based on the kinetic inductance inherent in any 1d quantum system. However, in order to measure that kinetic inductance electrical contact to the nanotube is required. Rather than using dc (”ohmic”) contact, we proposed to use a capacitive contact. A capacitive contact is in principle simple to achieve: any parallel plate close to the nanotube will be capacitively coupled to the nanotube. At GHz frequencies, this capacitance can behave as a short circuit, allowing efficient (i.e. low-impedance) high- frequency contact to a nanotube. However, for this to be the case, the length of the nanotube must be significant, even for parallel plates very close to the nanotube. Further reflection reveals that a capacitively contacted nan- otube has a distributed capacitance per unit length as well as a distributed kinetic inductance per unit length, thus forming an electrical transmission line. (This is a circuit description of the fundamental excitations in a L¨ uttinger liquid.) We further predicted that it would be possible to measure the wave velocity of this nano-transmission line by measuring the GHz electrical impedance from plate-to-plate, as shown in figure 1. For GHz resonant frequencies, nanotubes of order 100 μm in length must be grown. In this paper we present growth of nanotubes long enough to behave as electrical nano-resonators with resonant frequencies in the GHz range. Our nanotubes are grown using CVD. Our catalyst preparation is similar to that of Kong[3] but can be deposited using a lift-off procedure requiring only photolithography and standard photoresist, in contrast to that of Kong which required either electron beam lithography or UV lithography on PMMA. Our catalysts have allowed the growth of many Y-junction nanotubes, which we describe and analyze quantitatively. † Author to whom correspondence should be addressed. Email: pburke@uci.edu. = Fig. 1. Predicted effective circuit model for capacitively contacted nanotube. II. CATALYST PREPARATION Under methods developed in reference [3], alumina nanoparticles combined with transition metals are typically mixed in methanol and spun onto a wafer with pre-patterned PMMA wells. This requires either 1) electron beam or deep- UV lithography to pattern the PMMA directly, or 2) a multi- step process involving both PMMA and photoresist. (Methanol cannot be spun onto wells patterned into photoresist directly because it dissolves the photoresist.) We have developed a simplified method of depositing transition metal catalysts using an aqueous solvent for the nanoparticles and transition metal catalysts. Using conventional photolithography we fabricate wells di- rectly in photoresist (Shipley 1827) on a 4” silicon wafer (100, p-type, resistivity 12-16 kΩ-cm) with its native oxide. Next, 2.0 g of alumina nanoparticles (Degussa, aluminum oxide C), 2.5 mmol of Fe(NO 3 ) 3 •9H 2 O (Aldrich), and 0.7 mmol of MoO 2 (acac) 2 (Aldrich) are added to 60 ml DI water in sequence while violently stirring. Since the Fe(NO 3 ) 3 is 10 μm Fig. 2. SEM image of a single walled carbon nanotube. Length is 60 μm. 0-7803-7977-2/03/$17.00 (C) IEEE [C026]