RESUMEN
Three-dimensional (3D) graphene microstructures have the potential to boost performance in high-capacity batteries and ultrasensitive sensors. Numerous techniques have been developed to create such structures; however, the methods typically rely on structural supports, and/or lengthy post-print processing, increasing cost and complexity. Additive manufacturing techniques, such as printing, show promise in overcoming these challenges. This study employs aerosol jet printing for creating 3D graphene microstructures using water as the only solvent and without any post-print processing required. The graphene pillars exhibit conductivity immediately after printing, requiring no high-temperature annealing. Furthermore, these pillars are successfully printed in freestanding configurations at angles below 45° relative to the substrate, showcasing their adaptability for tailored applications. When graphene pillars are added to humidity sensors, the additional surface area does not yield a corresponding increase in sensor performance. However, graphene trusses, which add a parallel conduction path to the sensing surface, are found to improve sensitivity nearly 2×, highlighting the advantages of a topologically suspended circuit construction when adding 3D microstructures to sensing electrodes. Overall, incorporating 3D graphene microstructures to sensor electrodes can provide added sensitivity, and aerosol jet printing is a viable path to realizing these conductive microstructures without any post-print processing.
RESUMEN
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 104 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.
