Patterned Liquid Metal Contacts for Printed Carbon Nanotube Transistors

Abstract

Flexible and stretchable electronics are poised to enable many applications that cannot be realized with traditional, rigid devices. One of the most promising options for low-cost stretchable transistors are printed carbon nanotubes (CNTs). However, a major limiting factor in stretchable CNT devices is the lack of a stable and versatile contact material that forms both the interconnects and contact electrodes. In this work, we introduce the use of eutectic gallium-indium (EGaIn) liquid metal for electrical contacts to printed CNT channels. We analyze thin-film transistors (TFTs) fabricated using two different liquid metal deposition techniques-vacuum-filling polydimethylsiloxane (PDMS) microchannel structures and direct-writing liquid metals on the CNTs. The highest performing CNT-TFT was realized using vacuum-filled microchannel deposition with an in situ annealing temperature of 150 °C. This device exhibited an on/off ratio of more than 10 and on-currents as high as 150 μA/mm-metrics that are on par with other printed CNT-TFTs. Additionally, we observed that at room temperature the contact resistances of the vacuum-filled microchannel structures were 50% lower than those of the direct-write structures, likely due to the poor adhesion between the materials observed during the direct-writing process. The insights gained in this study show that stretchable electronics can be realized using low-cost and solely solution processing techniques. Furthermore, we demonstrate methods that can be used to electrically characterize semiconducting materials as transistors without requiring elevated temperatures or cleanroom processes.

Liquid Metal–Based Soft Microfluidics

“…With this method, liquid metal leakage due to injection pressure is reduced while complete filling of the microchannels can be achieved in a hands‐free manner. Furthermore, Andrews et al found that the use of vacuum filling technique improves the contact resistance of liquid metal with carbon nanotube transistor, most likely due to improved adhesion of the liquid metal and conformal coverage of the surface compared with direct writing (see Figure b).…”

“…b) Two ways of preparing soft contact electrodes after depositing carbon nanotubes: Direct writing and vacuum filling of liquid metal, and corresponding optical microscope images of LM patterns. Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…In recent years, various strategies have been explored to develop corrosion resistant coatings for flexible electronics and to improve the LM patterning techniques on soft substrates . Dickey and Franklin et al reported the use of printed carbon nanotubes as flexible electrode and interconnect material, which was used in conjunction with EGaIn to form reliable thin‐film transistors (TFTs). The EGaIn LM can be deposited by both the vacuum‐filling PDMS microchannel structures and direct‐writing on CNTs.…”

Shear‐Driven Direct‐Write Printing of Room‐Temperature Gallium‐Based Liquid Metal Alloys

“…[35,55] It is difficult to characterize the fundamental interfacial properties between liquid metal and various surfaces due to the presence of the oxide. [35,55] It is difficult to characterize the fundamental interfacial properties between liquid metal and various surfaces due to the presence of the oxide.…”

Carbon Nanostructures for Energy and Sensing Applications

“…erefore, there is a prodigious need for more economic and efficient technologies for energy storage and sensors for healthcare and environmental monitoring application. e advancement of carbon nanostructured materials, dimensions ranging from tens to several hundreds of nm, dating back to the past few years, has seen a tremendous scientific growth in the field of battery and supercapacitor [1], bio, chemical, and mechanical sensors [2][3][4][5][6], and possible related applications as illustrated in Figure 1 [7][8][9][10][11][12][13][14][15]. ese nanostructured carbon materials own unique characteristics, such as superior electrical conductivity, tunable porosity, outstanding mechanical strength, and remarkable thermal, optical, and chemical properties because of their nanosized and very high surface-area-to-volume ratio [16,17].…”