Comparative study of solution-processed carbon nanotube network transistors

Abstract

Carbon nanotube networks in thin-film type transistors were studied experimentally, comparing the use of pre-separated semiconducting enriched nanotubes (90% and 99% purity) to examine how topology affects the properties of the devices. Measurements are reported for two deposition methods used for network formation: random and spin-aligned deposition methods. The results show that the thin-film transistors fabricated via spin-aligned deposition demonstrate better electrical uniformity and performance than those produced by the random network deposition method. Our results imply that coverage and alignment are strongly correlated with the properties of the devices and should therefore be simultaneously optimized for improved electrical uniformity and performance.Networks of single-walled carbon nanotubes (SWNTs) represent a class of electronic materials that can serve as high-performance channel layers in thin-film field effect transistors (TFTs) and other devices. 1-5 The favorable properties of such films may provide a route to practical nanotube-based electronic systems by eliminating the need for precise control over the properties or positions of individual SWNTs. Although single-tube devices can potentially achieve the intrinsic mobility of a semiconducting SWNT, 6 single-tube assembly methods are extremely challenging to scale up and are not yet technologically practical for largearea applications. Therefore, thin films of SWNTs consisting of either random or well-aligned networks represent a promising path to scalable device manufacturing. 7,8 However, such films may have a lower mobility than single-tube devices because tube-tube crossings limit the current flow from source to drain when the channel length is greater than the nanotube length. 9,10 Increasing the network density can increase the current but can also lead to a shorted TFTs 11 resulting from a detrimental increase in the probability of having a percolation path dominated by metallic species.The problem of the co-existence of metallic and semiconducting SWNTs can be addressed by using pre-purified semiconducting enriched SWNTs produced, for example, by density gradient ultracentrifugation. 12 However, limitations are also imposed in this process because cost-effective, 100% pure semiconducting nanotubes are not available. Therefore, all commercially available enriched solutions contain some amount of metallic nanotubes, which may negatively impact semiconducting device properties. To date, there has been progressive research based on highly preenriched semiconducting nanotubes (i.e., over 95% semiconducting nanotubes). 13,14 Nevertheless, many interesting issues remain to be studied. Open questions include whether improved performance can be achieved with separated nanotubes of lower enrichment (<95%) and how does network topology affect the transport and uniformity properties. 15 Here, we present the results of experimental studies designed to address these questions by evaluating the transport and uniformity properties of transistors fabric...

Nanomaterials in transistors: From high-performance to thin-film applications

“…It is less favorable to have tightly packed (~0-nm pitch) arrays of CNTs for highperformance transistors (62), as they will result in deleterious charge screening effects and challenges for establishing good electrical contacts. Requirements for TFTs are much more relaxed, where even tangled films of CNTs with no alignment can be used (69)(70)(71). The 2D nanomaterials do offer planar coverage, but it is difficult to transfer the films without inducing defects that are detrimental to transistor performance.…”

“…I, current; V, voltage; I d , drain current. solution onto a substrate to form a thin film (the cheapest fabrication approach possible, as it is amenable for printing processes) consistently deliver mobilities of 10 to 100 cm 2 V −1 s −1 (69)(70)(71)(93)(94)(95). Further efforts to induce alignment in the CNT thin films could boost mobility much higher than 100 cm 2 V −1 s −1 (68), which would be revolutionary performance improvement for TFTs processed in solution phase.…”

Highly selective sorting of semiconducting single wall carbon nanotubes exhibiting light emission at telecom wavelengths

“…For larger source-drain distances, it is known that I D -V GS characteristics with acceptable ON/OFF ratios can be obtained if the nanotube density is kept low enough to prevent the formation of percolating pathways through m-SWNTs [14][15][16]. The low density would result in a limited drive current, which is generally too low for most applications.…”

“…The presence of m-SWNTs could be notably detrimental to the optical emission as they quench the photoluminescence (PL) signal of semiconducting SWNTs (s-SWNTs) by means of inter-nanotube relaxation [11][12][13]. m-SWNTs can also degrade carbon nanotube-FET characteristics as they prevent the use of high density nanotube networks by reducing the ON/OFF current ratio to unacceptable values [14][15][16]. In addition, significant advantages are expected when Nano Res.…”

Differentiation of Complex Vapor Mixtures Using Versatile DNA–Carbon Nanotube Chemical Sensor Arrays

“…The approach was adapted from earlier reports. 17,18 Care was taken to develop a method that ensured the production of reproducible arrays of NT transistors where the channel consisted of a relatively sparse NT network (see Fig. 1a).…”