Direct
drawing techniques have contributed to the ease of patterning
soft electronic materials, which are the building blocks of analog
and digital integrated circuits. In parallel with the printing of
semiconductors and electrodes, selective deposition of gate insulators
(GI) is an equally important factor in simplifying the fabrication
of integrated devices, such as NAND and NOR gates, and memory devices.
This study demonstrates the fabrication of six types of printed GI
layers (high/low-k polymer and organic–inorganic
hybrid material), which are utilized as GIs in organic field-effect
transistors (OFETs), using the electrostatic-force-assisted dispensing
printing technique. The selective printing of GIs on the gate electrodes
enables us to develop practical integrated devices that go beyond
unit OFET devices, exhibiting robust switching performances, non-destructive
operations, and high gain values. Moreover, the flexible integrated
devices fabricated using this technique exhibit excellent operational
behavior. Therefore, this facile fabrication technique can pave a
new path for the production of practical integrated device arrays
for next-generation devices.
A novel fluorinated organic–inorganic (O–I) hybrid sol—gel based material, named FAGPTi, is successfully synthesized and applied as a gate dielectric in flexible organic thin‐film transistors (OTFTs). The previously reported three‐arm‐shaped alkoxysilane‐functionalized amphiphilic polymer yields a stable O–I hybrid material consisting of uniformly dispersed nanoparticles in the sol‐state. Here, a fluorinated precursor is introduced into the system, making it possible to realize more stable spherical composites. This results in long‐term colloidal stability (≈1.5 years) because composite growth is strongly inhibited by the presence of fluorine groups with intrinsically strong repulsive forces. Additionally, the FAGPTi film is easily deposited via thermally annealed sol–gel reactions; the films can be successfully fabricated through the printing method, and exhibit excellent flexibility and enhanced insulating properties compared to existing materials. OTFTs with FAGPTi layers show highly stable driving characteristics under severe bending conditions (1.9% strain). Integrated logic devices are also successfully operated with these OTFTs. Additionally, it can facilely be applied to amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) TFT devices other than OTFT. Therefore, this synthetic strategy can provide useful insights into the production of functional O–I hybrid materials, enabling the efficient fabrication of electronic materials and devices exhibiting these properties.
A π-conjugated
polymer semiconductor, PBDTTTffPI, was synthesized
for use as an organic semiconductor suitable for electrohydrodynamic
(EHD) jet printing technology. Bulky alkylation of the polymer gave
PBDTTTffPI good solubility in several organic solvents. EHD jet printing
using PBDTTTffPI ink produced direct patterns of polymer semiconductors
while maintaining smooth surface morphologies and crystal structures
similar to those of spin-coated PBDTTTffPI films. EHD-jet-printed
PBDTTTffPI was appropriate for use as a semiconductor layer in organic
field-effect transistors (OFETs) and logic gates. OFETs that used
EHD-jet-printed PBDTTTffPI had better electrical characteristics than
devices that used spin-coated semiconductor films. When a dielectric
material (Al2O3) with a high dielectric constant
was introduced, the jet-printed PBDTTTffPI operated well at low voltages.
Integrated devices such as inverters, NAND gates, and NOR gates were
fabricated by printing PBDTTTffPI patterns and showed good switching
behaviors. Therefore, the use of printable PBDTTTffPI provides an
advance toward fabrication of practical integrated arrays in next-generation
devices.
Solution-based printing has contributed to the facile deposition of various types of materials, including the building blocks of printed electronics. In particular, solution-processable organic semiconductors (OSCs) are regarded as one of the most fascinating candidates for the fabrication of printed electronics. Herein, we report electrohydrodynamic (EHD) jet-printed p-and n-type OSCs, namely 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS−PEN) and 6,13-bis((triisopropylsilyl)ethynyl)-5,7,12,14tetraazapentacene (TIPS−TAP), and their use as single-OSC layers and as OSC mixed p−n layers to fabricate solutionprocessed p-, n-, and ambipolar-type organic field-effect transistors (OFETs). Use of the dragging mode of EHD jet printing, a process driven under a low electrostatic field with a short nozzle-to-substrate distance, was found to provide favorable conditions for growth of TIPS−PEN and TIPS−TAP crystals. In this way, the similar molecular structures of TIPS−PEN and TIPS−TAP yielded a homogeneous solid solution and showed ambipolar transport properties in OFETs. Therefore, the combination of single-and mixed-OSC layers enabled the preparation of various charge-transported devices from unit to integrated devices (NOT, NAND, NOR, and multivalued logic). Therefore, this fabrication technology can be useful for assisting in the production of OSC layers for practical applications in the near future.
Engineering
the energy levels of organic conducting materials can
be useful for developing high-performance organic field-effect transistors
(OFETs), whose electrodes must be well controlled to facilitate easy
charge carrier transport from the source to drain through an active
channel. However, symmetric source and drain electrodes that have
the same energy levels are inevitably unfavorable for either charge
injection or charge extraction. In this study, asymmetric source and
drain electrodes are simply prepared using the electrohydrodynamic
(EHD)-jet printing technique after the careful work function engineering
of organic conducting material composites. Two types of additives
effectively tune the energy levels of poly(3,4-ethylenedioxythiophene)
polystyrene sulfonate-based composites. These solutions are alternately
patterned using the EHD-jet printing process, where the use of an
electric field makes fine jet control that enables to directly print
asymmetric electrodes. The asymmetric combination of EHD-printed electrodes
helps in obtaining advanced charge transport properties in p-type
and n-type OFETs, as well as their organic complementary inverters.
This strategy is believed to provide useful guidelines for the facile
patterning of asymmetric electrodes, enabling the desirable properties
of charge injection and extraction to be achieved in organic electronic
devices.
Development of stretchable wearable devices requires essential materials with high level of mechanical and electrical properties as well as scalability. Recently, silicone rubber-based elastic polymers with incorporated conductive fillers (metal particles, carbon nanomaterials, etc.) have been shown to the most promising materials for enabling both high electrical performance and stretchability, but the technology to make materials in scalable fabrication is still lacking. Here, we propose a facile method for fabricating a wearable device by directly coating essential electrical material on fabrics. The optimized material is implemented by the noncovalent association of multiwalled carbon nanotube (MWCNT), carbon black (CB), and silicon rubber (SR). The e-textile sensor has the highest gauge factor (GF) up to 34.38 when subjected to 40% strain for 5,000 cycles, without any degradation. In particular, the fabric sensor is fully operational even after being immersed in water for 10 days or stirred at room temperature for 8 hours. Our study provides a general platform for incorporating other stretchable elastic materials, enabling the future development of the smart clothing manufacturing.
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