High‐Performance Partially Aligned Semiconductive Single‐Walled Carbon Nanotube Transistors Achieved with a Parallel Technique

Abstract

Single-walled carbon nanotubes (SWNTs) are widely thought to be a strong contender for next-generation printed electronic transistor materials. However, large-scale solution-based parallel assembly of SWNTs to obtain high-performance transistor devices is challenging. SWNTs have anisotropic properties and, although partial alignment of the nanotubes has been theoretically predicted to achieve optimum transistor device performance, thus far no parallel solution-based technique can achieve this. Herein a novel solution-based technique, the immersion-cum-shake method, is reported to achieve partially aligned SWNT networks using semiconductive (99% enriched) SWNTs (s-SWNTs). By immersing an aminosilane-treated wafer into a solution of nanotubes placed on a rotary shaker, the repetitive flow of the nanotube solution over the wafer surface during the deposition process orients the nanotubes toward the fluid flow direction. By adjusting the nanotube concentration in the solution, the nanotube density of the partially aligned network can be controlled; linear densities ranging from 5 to 45 SWNTs/μm are observed. Through control of the linear SWNT density and channel length, the optimum SWNT-based field-effect transistor devices achieve outstanding performance metrics (with an on/off ratio of ~3.2 × 10(4) and mobility 46.5 cm(2) /Vs). Atomic force microscopy shows that the partial alignment is uniform over an area of 20 × 20 mm(2) and confirms that the orientation of the nanotubes is mostly along the fluid flow direction, with a narrow orientation scatter characterized by a full width at half maximum (FWHM) of <15° for all but the densest film, which is 35°. This parallel process is large-scale applicable and exploits the anisotropic properties of the SWNTs, presenting a viable path forward for industrial adoption of SWNTs in printed, flexible, and large-area electronics.

Principles of carbon nanotube dielectrophoresis

“…However, due to an inefficient growth-control over CNT chirality in this way, metallic (m-) SWCNTs, to some extent, are always present in devices, significantly suppressing device performance. Comparatively, solution-based post-assembly methods, such as shear-force guided SWCNT alignment [23,24] is known to lack fine-control over CNT orientations and locations. The Langmuir-Schaefer method [25,26], a widely used technique for fabricating molecular thin films, illustrates inefficiency in assembling monolayer SWCNT arrays, thus detrimental to transistor performances because of the increased inter-tube electrostatic screening effect in multilayer assemblies.…”

Covalent Atomic Bridges Enable Unidirectional Enhancement of Electronic Transport in Aligned Carbon Nanotubes

“…Our finding have implications in the field of anisotropic conduction which is of great scientific and technological interest. Aligned SWNTs have been used as the building blocks of high performance transistors [33][34][35][36][37] , light-emitting diodes, 38 logic gates, 39 radio-frequency devices, 40 transparent conductive films, 41 sensors, 42,43 , photodetectors and photoswitches 44 and synaptic transistors. 45 The ability to modulate the transport properties of aligned SWNTs in a controlled manner offers a route to expand the functionality of these technologies.…”

Directed and On‐Demand Alignment of Carbon Nanotube: A Review toward 3D Printing of Electronics

“…In the case of polymer/CNTs composite, it is found that the CNTs tend to align 45° from the radial direction and independent of radial position and spin rate . The reported degree of alignment of the CNTs for the rotary spin method is half‐maximum‐full‐width (HMFW) of around <15° . This method is simple and robust; however, it has several limitations such as poor alignment at the center region and no control over the direction of alignment.…”