Geometry Dependent Resistivity in Single-Walled Carbon Nanotube Films Patterned Down to Submicron Dimensions
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Geometry Dependent Resistivity in Single-Walled Carbon Nanotube Films Patterned Down to Submicron Dimensions Ashkan Behnam1, Leila Noriega1, Yongho Choi1, Zhuangchun Wu2, Andrew G Rinzler2, and Ant Ural1 1 Electrical and Computer Engineering, University of Florida, Gainesville, FL, 32611 2 Physics, University of Florida, Gainesville, FL, 32611 ABSTRACT We demonstrate patterning of SWNT films down to 200 nm lateral dimensions using e-beam lithography and reactive ion etching with good selectivity and directionality. We then use this etch capability to fabricate standard four-point-probe structures to characterize the resistivity of these films as a function of device geometry. The resistivity of nanotube films are found to be independent of device length for a given width and thickness, while increasing over three orders of magnitude compared to bulk films, as the width and the thickness of the films shrink. In particular, we find that the resistivity of SWNT films starts to increase with decreasing device width below 20 µm, exhibiting an inverse power law dependence on device width at submicron dimensions. We show that this behavior can be explained by a purely geometrical argument. INTRODUCTION AND BACKGROUND Studies on the electrical and physical characteristics of single-walled carbon nanotubes (SWNTs) have proven their intrinsic advantages over conventional materials for several device applications [1]. However, controlling nanotubes’ chirality, diameter, location, and direction on the substrate requires several purification or fabrication steps, which makes mass production of single nanotube-based devices with acceptable quality and yield rather difficult [2]. Recently, there has been a growing interest in using 2D nanotube networks and 3D nanotube films as a class of materials, in which individual variations in diameter and chirality are ensemble averaged to yield uniform physical and electronic properties. Several applications of SWNT networks and films have recently been demonstrated, such as thin film transistors (TFTs) [3-5], flexible electronics [6,7], sensors [8,9], and transparent and conductive electrodes for optoelectronics [10,11]. All of these potential applications require patterning of the nanotube films and understanding their electrical properties as a function of device geometry. Although 2D nanotube networks and films have been patterned recently by a variety of techniques including the use of a CO2 snow jet [3], transfer printing [12,13], and O2 plasma etching [4,14] in the micron regime, reproducible patterning of thicker nanotube films down to submicron linewidths has not been demonstrated previously. Furthermore, while a few groups have recently studied the electrical properties of dilute 2D nanotube networks as a function of device length and nanotube density [3,15,16], and those of nanotube films as a function of film thickness [17], how electrical properties of nanotube films scale as a function of device geometry, particularly device width (perpendicular to the direction
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