High-fidelity patterning of thin metal films on arbitrary soft substrates promises integrated circuits and devices that can significantly augment the morphological functionalities of freeform electronics. However, existing patterning methods that decisively rely on prefabricated rigid masks are severely incompatible with myriad surfaces. Here, we report printable, stretchable metal-vapor-desorption layers (s-MVDLs) that can enable high-fidelity patterning of thin metal films on freeform polymeric surfaces. The printed rubbery matrix with highly mobile chains effectively repels various metal vapors from the surface and inhibits their condensation, thereby allowing selective metal deposition. The s-MVDLs are printed by direct ink writing techniques, enabling customizable and scalable thin metal patterns ranging from the micrometer to millimeter scale with high fidelity. Furthermore, the superior stretchability and mechanical robustness of the s-MVDLs allow highly compliant deformation along the substrates, enabling the construction of unconventional circuits and devices on multi-curvature, non-developable, and stretchable surfaces. Existing patterning methods for thin metal films rely on prefabricated rigid masks incompatible with soft substrates. Here, the authors report printable and stretchable metal-vapor-desorption layers that facilitate high-fidelity patterning, enabling circuits and devices on 3D curvilinear and stretchable substrates.
In this letter, we improved the stability of all-inkjet-printed carbon nanotube thin film transistors (CNT TFTs) by employing a double gate (DG) structure under an optimal bias condition. In the single-gate structure, the positive threshold voltage (VTH) shift under 10 V positive gate bias stress (PGBS) was significantly reduced with poly(4-vinylphenol) passivation. However, after 100 s, the on-current level was decreased, and a large negative VTH shift was observed. We adopted DG CNT TFTs for a further improvement. When -3 V was applied to the top gate, the DG CNT TFTs not only exhibited a much lower VTH shift but also showed a stabilized on-current level. When an appropriate bias is applied to the top gate, charge trapping is induced at the top gate interface and it might balance between the positive and negative shifts. As a result, the overall stress effect is reduced. The p-type only inverter adopting a DG CNT TFT showed improved stability under -3 V of top gate bias. Our experimental result shows that DG structure is a promising candidate for various CNT circuit designs.
Abstract Improving the performance of solution-processed single-walled carbon nanotube thin film transistors (SWCNT TFTs) is essential to their wide usage in next generation large-area electronic devices. However, uncontrollable tube-tube junction and random network formation from conventional solution processes of SWCNTs has limited mobility and on-current level of SWCNT TFTs. Herein, we demonstrate a facile method by switching idea of reducing coffee-ring of the conventionally solution-processed or inkjet-printed thin films. Spontaneous coffee-ring formation of the inkjet-printed droplets is found to enhance directional alignment of SWCNTs in the outer rim of the coffee-rings. The evaporation-driven capillary flow toward the rim inside induces migration of SWCNT and thus forms densely aligned SWCNT rings. Periodic connection of such rings can provide high-current path at a given voltage. Therefore, by additionally forming the periodically connected rings on a pre-established random network of SWCNT in channel area of TFTs, we significantly improved the mobility and I on / I off ratio of SWCNT TFTs without degradations in other electrical parameters such as threshold voltage and subthreshold swing. We also demonstrated all-solution-processed inverters with higher voltage-gain in comparison with conventional ones.
Stretchable Displays In article number 2201067, Yeongjun Lee, Yongtaek Hong, Youngjun Yun, and co-workers review recent developments in advanced materials and feasible strategies for the realization of stretchable electronic devices for stretchable displays, which will be the ultimate form factor for next-generation displays. Various advanced stretchable matrix displays as well as future prospect of stretchable active displays are discussed.
Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have gained considerable attention as an emerging semiconductor due to their promising atomically thin film characteristics with good field-effect mobility and a tunable band gap energy. However, their electronic applications have been generally realized with conventional inorganic electrodes and dielectrics implemented using conventional photolithography or transferring processes that are not compatible with large-area and flexible device applications. To facilitate the advantages of 2D TMDCs in practical applications, strategies for realizing flexible and transparent 2D electronics using low-temperature, large-area, and low-cost processes should be developed. Motivated by this challenge, we report fully printed transparent chemical vapor deposition (CVD)-synthesized monolayer molybdenum disulfide (MoS2) phototransistor arrays on flexible polymer substrates. All the electronic components, including dielectric and electrodes, were directly deposited with mechanically tolerable organic materials by inkjet-printing technology onto transferred monolayer MoS2, and their annealing temperature of <180 °C allows the direct fabrication on commercial flexible substrates without additional assisted-structures. By integrating the soft organic components with ultrathin MoS2, the fully printed MoS2 phototransistors exhibit excellent transparency and mechanically stable operation.
A newly-designed multi-dipping technique of semiconducting single-walled carbon nanotubes (SWCNTs) enables easy implementation of flexible/stretchable solution-processed SWCNT thin-film transistors (TFTs) in a very short time. Using commercialized aqueous SWCNT ink, repetition of deionized (DI) water rinsing during multi-dipping process makes possible the rapid deposition of a dense and high quality SWCNT network formation, thus leading to significant reduction in total fabrication time but improved electrical performances for SWCNT TFTs. The image shows deposition mechanisms for conventional one-time dipping (left) and multi-dipping techniques (right). Further details can be found in the article number 1901413 by Taehoon Kim, Yongtaek Hong and co-workers.
Abstract Inkjet and transfer printing processes are combined to easily form patterned poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as top anodes of all solution–processed inverted polymer light emitting diodes (PLEDs) on rigid glass and flexible plastic substrates. An adhesive PEDOT:PSS ink is formulated and fully customizable patterns are obtained using the inkjet printing process. In order to transfer the patterned PEDOT:PSS films, adhesion properties at interfaces during multistep transfer printing processes are carefully adjusted. The transferred PEDOT:PSS film on the plastic substrates shows not only a sheet resistance of 260.6 Ω/□ and a transmittance of 92.1% at 550 nm wavelength but also excellent mechanical flexibility. The PLEDs with spin‐coated functional layers sandwiched between the transferred PEDOT:PSS top anodes and inkjet‐printed Ag bottom cathodes are fabricated. The fabricated PLEDs on the plastic substrates show a high current efficiency of 10.4 cd A −1 and high mechanical stability. It is noted that because both Ag and PEDOT:PSS electrodes can be patterned with a high degree of freedom via the inkjet printing process, highly customizable PLEDs with various pattern sizes and shapes are demonstrated on the glass and plastic substrates. Finally, with all solution process, a 5 × 7 passive matrix PLED array is demonstrated.
Implementing the multilayered structure on a stretchable platform is essential to realize a multifunctional system beyond simply imparting stretchability to a single rigid device. There have been many efforts to achieve a stretchable vertical interconnect access (VIA) for electrical connections between two or more different layers on stretchable electronics. Nevertheless, there are still challenges in implementing soft multifunctional systems with the stretchable VIA due to high complexity of the fabrication process, limitations on the circuit design, and poor compatibility with other circuit components. Here, we report a microstructured elastomer composite-based VIA that is compatible with the facile bottom-up process for multilayered structures. By applying the magnetic field to the elastomer composite of highly conductive ferromagnetic particles with core–shell structure, conductivity of the composite is greatly enhanced with filamentous structures. The design of microstructures is optimized through systematic analysis of the structural simulation and surface-strain mapping. When the substrate is stretched, microstructures efficiently disperse the mechanical stress concentrated at the interface between VIA and the substrate, which originates from the difference in Young's modulus, resulting in the enhancement of mechanical reliability. Because VIAs and electrodes are monolithically embedded on the substrate during the process of stacking one layer on top of the underlying layer, the proposed VIA is suitable for implementing multilayered structures in a bottom-up method. To show the feasibility of our approach to multilayered stretchable electronics applications, various types of VIAs with four layers and passive matrix-stretchable LED arrays are successfully demonstrated on the stretchable platform. We believe that the proposed microstructured VIA has the potential to play a major role in paving the way toward highly integrated stretchable electronics.
The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa
Soft pressure sensors play key roles as input devices of electronic skin (E-skin) to imitate real human skin. For efficient data acquisition according to stimulus types such as detailed pressure images or macroscopic strength of stimuli, soft pressure sensors can have variable spatial resolution, just like the uneven spatial distribution of pressure-sensing receptors on the human body. However, previous methods on soft pressure sensors cannot achieve such tunability of spatial resolution because their sensor materials and read-out electrodes need to be elaborately patterned for a specific sensor density. Here, we report a universal soft pressure-sensitive platform based on anisotropically self-assembled ferromagnetic particles embedded in elastomer matrices whose spatial resolution can be facilely tuned. Various spatial densities of pressure-sensing receptors of human body parts can be implemented by simply sandwiching the film between soft electrodes with different pitches. Since the anisotropically aligned nickel particles form independent filamentous conductive paths, the pressure sensors show spatial sensing ability without crosstalk, whose spatial resolution up to 100 dpi can be achieved from a single platform. The sensor array shows a wide dynamic range capable of detecting various pressure levels, such as liquid drops (∼30 Pa) and plantar (∼300 kPa) pressures. Our universal soft pressure-sensing platform would be a key enabling technology for actually imitating the receptor systems of human skin in robot and biomedical applications.
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