Fringing-field dielectrophoretic assembly of ultrahigh-density semiconducting nanotube arrays with a self-limited pitch

Abstract

One key challenge of realizing practical high-performance electronic devices based on singlewalled carbon nanotubes is to produce electronically pure nanotube arrays with both a minuscule and uniform inter-tube pitch for sufficient device-packing density and homogeneity. Here we develop a method in which the alternating voltage-fringing electric field formed between surface microelectrodes and the substrate is utilized to assemble semiconducting nanotubes into well-aligned, ultrahigh-density and submonolayered arrays, with a consistent pitch as small as 21±6 nm determined by a self-limiting mechanism, based on the unique field focusing and screening effects of the fringing field. Field-effect transistors based on such nanotube arrays exhibit record high device transconductance (450 mS mm À 1 ) and decent on current per nanotube (B1 mA per tube) together with high on/off ratios at a drain bias of À 1 V.

Directed Assembly of Ultrathin Gold Nanowires over Large Area by Dielectrophoresis

“…A successful experiment in a pattern containing 20 individual devices is accomplished as shown in Langmuir XXXX, XXX, XXX−XXX probes is demonstrated recently using fringing field. 41 The possibility of such an alignment, despite a small voltage leakage to the Si substrate that can happen through a 300 nm SiO 2 layer, is minimal in our case as we are applying the voltage directly to the probes. After this a postprocessing procedure is needed which involves FIB etching of the contact pads.…”

Origins and Characteristics of the Threshold Voltage Variability of Quasiballistic Single-Walled Carbon Nanotube Field-Effect Transistors

“…Better passivation schemes to reduce the interface fixed charges, improved sorting or synthesis techniques to minimize nanotube diameter distribution, 49À51 together with novel assembly techniques to reduce the pitch among nanotube arrays, 52,53 are likely required to further improve the variability performance of devices based on multiple-tube arrays and make SWNT logic electronics a practical technology.…”

Short channel carbon nanotube thin film transistors with high on/off ratio fabricated by two-step fringing field dielectrophoresis

“…Since the electric field is stronger near the electrodes during the dielectrophoresis, the alignment of the CNTs worsens at far from the electrodes and the density of the CNTs is also much lower and non-uniform [19][20][21][22]. Thus to obtain uniform CNT films in the channel area and hence the uniform devices performance, the L Ch should be limited to be short enough (L Ch \ L S ) [23]. Relatively higher current density and mobility are easily obtained in such short channel length devices with the aligned CNT films.…”

“…Thus the metallic CNTs are more easily assembled toward the electrodes [24], which tends to lower the I on /I off of the devices considering the relative short channel length. Recently, Cao et al [23] developed a fringing field dielectrophoresis method for CNTs assembling. Instead of a pair of planar electrodes used in conventional dielectrophoresis, vertically stacked electrodes were employed.…”

“…Dielectrophoresis has been reported to be an efficient way to align and assemble CNTs for the channel of field effect transistors [19][20][21][22][23]. Usually CNT solution was dropped onto a pair of planar electrodes on the substrate and an alternating current (AC) signal was forced onto the electrodes pair during the dielectrophoresis assembly of CNTs.…”