Controlled Assembly of High Density SWNT Networks on a Flexible Parylene-C Substrate C.-L. Chen 1,* , X. Xiong 2,* , A. Busnaina 2 , and M. R. Dokmeci 1 1 ECE Department, NSF Center for High Rate Nanomanufacturing, Northeastern University, Boston, MA 2 MIE Department, NSF Center for High Rate Nanomanufacturing, Northeastern University, Boston, MA chen.ch@neu.edu ABSTRACT In this paper, we present a directed assembly technique for controlled micro-patterning of Single-Walled Carbon Nanotubes (SWNTs) on a flexible parylene-C substrate for electronic applications. The presented large scale fabrication of ordered carbon nanotube arrays and networks is achieved by performing site-selective fluidic assembly of SWNTs on a plasma treated parylene-C substrate. Parylene-C, which is lightweight, mechanically strong and stress-free material deposited at room temperature, is an emerging substrate material for flexible devices. The uniformly deposited nanotube lateral structures are formed directly on the parylene-C substrate without utilizing printing or transfer techniques. Both electrical and structural characterizations are performed on the SWNT- based devices on the flexible substrate. The developed nanotube patterning on polymeric substrates has immediate applications in wearable electronics and sensors, flexible field effect transistors (FETs) and lateral interconnects. Keywords: Flexible Parylene-C substrates, Single-Walled Carbon Nanotubes, Nanoscale patterning, Dip coating. 1 INTRODUCTION Single-Walled Carbon Nanotubes (SWNTs) with their attractive properties such as large surface-to-volume ratio, high packing density and long-range order may serve as the potential building blocks for the next generation of nanoscale devices. [1, 2] The integration of ordered arrays of carbon nanotubes on to rigid as well as flexible substrates offers many opportunities for realizing novel multifunctional devices. [3-5] The transfer of vertically or horizontally aligned carbon nanotube structures are often realized utilizing complicated steps of site-selective CVD nanotube growth or conformal contact printing. [6, 7] The major problem of CVD based approach is the requirement of high processing temperatures (~800°C) which is not CMOS compatible and also can’t be applied to most polymeric devices. PDMS stamps are also utilized as an intermediate carrier to transfer-print SWNTs on to different substrates including plastic sheets. [8] Though challenging, it is highly desirable to fabricate integrated nanotube- polymer flexible electronic devices at room temperature in a simple and cost-effective way. Here, we present a novel technique for localized patterning of SWNT networks on a flexible Parylene-C substrate by utilizing surface controlled microfluidic assembly technique (Fig.1). Unlike most rigid substrates which can be chemically functionalized for large-scale assembly of carbon nanotubes, [9, 10] the soft polymer surfaces are hydrophobic and their properties cannot be easily altered chemically. The low surface energy makes the direct assembly of nanotubes on a hydrophobic surface a challenging task. To overcome these challenges, we developed a plasma treatment method to modify the surface properties of the polymer for effective direct assembly of carbon nanotubes onto its surface. The previous SWNT patterning approach used a PDMS substrate which was also flexible. [11] A major limitation of the previous approach, however, was the requirement of a shadow mask which limited the flexibility in pattern dimensions. In this study, we utilized photolithography for the large-scale assembly of SWNT arrays on parylene-C substrates. This versatile technology has direct applications in the realization of nanoscale devices on flexible substrates potentially useful in numerous fields including flexible electronics, wearable nanosensors, CNT-field effect transistors and lateral CNT interconnects. 2 FABRICATION PROCESS The fabrication process is shown in Fig.2 and starts with the deposition of a 10µm parylene-C layer on top of a *These authors contributed equally. Pulling direction Fig.1 Schematic drawing of the surface controlled microfluidic assembly technique. 16 NSTI-Nanotech 2008, www.nsti.org, ISBN 978-1-4200-8503-7 Vol. 1