Instantaneous Pulsed-Light Cross-Linking of a Polymer Gate Dielectric for Flexible Organic Thin-Film Transistors

High-Mobility Fungus-Triggered Biodegradable Ultraflexible Organic Transistors

Biodegradable organic field-effect transistors (OFETs) have drawn tremendous attention for potential applications such as green electronic skins, degradable flexible displays, and novel implantable devices. However, it remains a huge challenge to simultaneously achieve high mobility, stable operation and controllable biodegradation of OFETs, because most of the widely used biodegradable insulating materials contain large amounts of hydrophilic groups. Herein, it is firstly proposed fungal-degradation ultraflexible OFETs based on the crosslinked dextran (C-dextran) as dielectric layer. The crosslinking strategy effectively eliminates polar hydrophilic groups and improves water and solvent resistance of dextran dielectric layer. The device with spin-coated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) semiconductor and C-dextran dielectric exhibits the highest mobility up to 7.72 cm² V^-1 s^-1 , which is higher than all the reported degradable OFETs. Additionally, the device still maintains high performance regardless of in an environment humidity up to 80% or under the extreme bending radius of 0.0125 mm. After completion of their mission, the device can be controllably biodegraded by fungi without any adverse environmental effects, promoting the natural ecological cycles with the concepts of "From nature, for nature". This work opens up a new avenue for realizing high-performance biodegradable OFETs, and advances the process of the "green" electrical devices in practical applications.

Microstructures in All-Inkjet-Printed Textile Capacitors with Bilayer Interfaces of Polymer Dielectrics and Metal-Organic Decomposition Silver Electrodes

Soft printed electronics exhibit unique structures and flexibilities suited for a plethora of wearable applications. However, forming scalable, reliable multilayered electronic devices with heterogeneous material interfaces on soft substrates, especially on porous and anisotropic structures, is highly challenging. In this study, we demonstrate an all-inkjet-printed textile capacitor using a multilayered structure of bilayer polymer dielectrics and particle-free metal-organic decomposition (MOD) silver electrodes. Understanding the inherent porous/anisotropic microstructure of textiles and their surface energy relationship was an important process step for successful planarization. The MOD silver ink formed a foundational conductive layer through the uniform encapsulation of individual fibers without blocking fiber interstices. Urethane-acrylate and poly(4-vinylphenol)-based bilayers were able to form a planarized dielectric layer on polyethylene terephthalate textiles. A unique chemical interaction at the interfaces of bilayer dielectrics performed a significant role in insulating porous textile substrates resulting in high chemical and mechanical durability. In this work, we demonstrate how textiles' unique microstructures and bilayer dielectric layer designs benefit reliability and scalability in the inkjet process as well as the use in wearable electronics with electromechanical performance.

Facile Photo-cross-linking System for Polymeric Gate Dielectric Materials toward Solution-Processed Organic Field-Effect Transistors: Role of a Cross-linker in Various Polymer Types

Energy-efficient solution-processed organic field-effect transistors (OFETs) are highly sought after in the low-cost printing industry as well as for the manufacture of flexible and other next-generation devices. The fabrication of such electronic devices requires high-functioning insulating materials that are chemically and mechanically robust to avoid lowering insulating properties during the device fabrication process or utilization of devices. In this study, we report a facile, fluorinated, UV-assisted cross-linker series using a fluorophenyl azide (FPA), which reacts with the C-H groups of a conventional polymer. This demonstrates the application of the cross-linked films in OFET gate dielectrics. The effects of the cross-linkable chemical structure of the FPA series on the cross-linking chemistry, photopatternability, and dielectric properties of the resulting films are investigated for low/high-k or amorphous/crystalline polymeric gate dielectric materials. The characteristics of insulating layers and behavior of OFETs containing these cross-linked gate dielectrics (for example, leakage current density (J), hysteresis, and charge trap density) depend on the polymer type. Furthermore, an organic-based complementary inverter and various printable OFETs with excellent electrical characteristics are successfully fabricated. Thus, these reported cross-linkers that enable the solution process and patterning of well-developed conventional polymer dielectric materials are promising for the realization of a more sustainable next-generation industrial technology for flexible and printable devices.

Transparent and Colorless Polyimides Containing Multiple Trifluoromethyl Groups as Gate Insulators for Flexible Organic Transistors with Superior Electrical Stability

A suitable insulating polymer material that is compatible with the fabrication process of organic transistors and has excellent electrical properties is critically required for the next-generation flexible organic electronics. In this study, using a one-step polymerization method, we synthesized two different solution-processable polyimides (PIs) incorporated with abundant trifluoromethyl groups. Not only were the two resulting PIs-termed 6FDA-6FDAM-PI and 6FDA-TFMB-PI-well soluble in organic solvents, but also they showed transparent and colorless optical properties. The fluorinated PI films showed smooth surface topographies and surface energy values that were appropriate for their use in bottom-gate organic transistors. Organic transistors separately fabricated with 6FDA-6FDAM-PI and 6FDA-TFMB-PI as the gate insulators showed excellent device performance and electrical stability under various testing conditions, especially for pentacene-based devices. The excellent performance of the devices with fluorinated PIs was attributed to the enhanced microstructure of the organic semiconductor and the fluorine-rich characteristic of the underlying gate insulator. Furthermore, organic complementary circuits including the basic logic gates of NOT, NOR, and NAND were demonstrated using these devices.

Stretchable Polymer Gate Dielectric by Ultraviolet-Assisted Hafnium Oxide Doping at Low Temperature for High-Performance Indium Gallium Tin Oxide Transistors

This paper reports the fabrication of indium gallium tin oxide (IGTO) thin-film transistors (TFTs) with ultraviolet (UV)-treated PVP- co-PMMA-based hybrid gate insulators at an extremely low temperature (≤150 °C). Synergetic hafnia loading and UV treatment were used to tailor the mechanical softness and hydroxyl fraction in the polymer dielectric film. The UV-treated hybrid dielectric film had a low hydroxyl concentration, a smoother surface, and a denser packing nature, which can be explained by the high ionicity of hafnium oxide and photon-assisted improvement in the cohesion between organic and inorganic materials. Suitability of the UV-treated hybrid dielectric film as a gate insulator was evaluated by fabricating bottom gate TFTs with sputtered IGTO films as a channel layer, which showed high carrier mobility at a low temperature. The resulting IGTO TFTs with a UV-treated hybrid gate insulator exhibited a remarkable high field-effect mobility of 25.9 cm²/(V s), a threshold voltage of -0.2 V, a subthreshold gate swing of 0.4 V/decade, and an I_ON/OFF ratio of >10⁷ even at a low annealing temperature of 150 °C. The fabricated IGTO TFTs with the UV-treated hybrid dielectric film on the plastic substrate were shown to withstand the 100 times mechanical bending stress even under an extremely small curvature radius of 1 mm due to the intrinsic stretchability of the hybrid dielectric film.

Mechanistic Analysis of Embedded Copper Oxide in Organic Thin-Film Transistors with Controllable Threshold Voltage

The modulation of threshold voltage (V _TH) of organic thin-film transistors (OTFTs) was investigated by embedding a thin CuO layer between the two semiconductor layers. The results showed that the V _TH of OTFTs with a CuO layer can be effectively tuned by controlling the positive gate-to-source voltage (V _GS0) under stress of gate-to-source voltages. The V _TH shifts from -3.67 to -0.82 V when the positive V _GS0 varies from 30 to 50 V. This can be explained by the mechanism of trapping electrons at the interface between the CuO charge-separation layer and the active layer. To confirm the role of the CuO layer acting as the charge-separation source, two organic thin-film diodes, indium-tin oxide(ITO)/tris (8-quinolinolato) aluminum(III) (Alq₃)/pentacene/Al (inverted-stack diode) and ITO/Alq₃/CuO/pentacene/Al (inverted-stack diode with a CuO layer), were fabricated and their diode current characteristics were measured. For the second device, a large current flow was observed at positive bias on the ITO electrodes, which is ascribed to the internal bipolar charge separation within the added CuO zone.

Plasma Polymerization Enabled Polymer/Metal-Oxide Hybrid Semiconductors for Wearable Electronics

A facile fabrication of polymer/metal-oxide hybrid semiconductors is introduced to overcome the intrinsically brittle nature of inorganic metal-oxide semiconductors. The fabrication of the hybrid semiconductors was enabled by plasma polymerization of polytetrafluoroethylene (PTFE) via radio frequency magnetron sputtering process which is highly compatible with metal-oxide semiconductor manufacturing facilities. Indium-gallium-zinc oxide (IGZO) and PTFE are cosputtered to fabricate PTFE-incorporated IGZO thin-film transistors (IGZO:PTFE TFTs) and they exhibit a field-effect mobility of 10.27 cm² V^-1 s^-1, a subthreshold swing of 0.38 V dec^-1, and an on/off ratio of 1.08 × 10⁸. When compared with conventional IGZO TFTs, the IGZO:PTFE TFTs show improved stability results against various electrical, illumination, thermal, and moisture stresses. Furthermore, the IGZO:PTFE TFTs show stable electrical characteristics with a threshold voltage ( V_th) shift of 0.89 V after 10 000 tensile bending cycles at a radius of 5 mm.

Intense pulsed light (IPL) annealed sol-gel derived ZnO electron injector for the production of high efficiency inverted quantum dot light emitting devices (QLEDs)

Room temperature intense pulsed light annealing (photonic annealing, pulsed forge) renders the sol-gel derived ZnO films highly conductive and hydrophobic with improved interface with the colloidal quantum dots. The IPL annealed ZnO proved to be a better electron transporter/injector in inverted devices with QDs. Both the current and power efficiencies of red devices comprising IPL annealed ZnO were 13.75 and 37.5 fold higher than the identical devices produced with thermally annealed ZnO. The lifetime of the devices with IPL annealed ZnO was found to be fivefold longer than the thermally annealed ZnO counterpart. Thermally aged devices comprising IPL annealed ZnO gave a maximum current efficiency of 23 cd A-1 and a power efficiency of 30 lm W-1.

Boosting Electrical Performance of High-κ Nanomultilayer Dielectrics and Electronic Devices by Combining Solution Combustion Synthesis and UV Irradiation

In the past decade, solution-based dielectric oxides have been widely studied in electronic applications enabling the use of low-cost processing technologies and device improvement. The most promising are the high-κ dielectrics, like aluminum (AlO_x) and hafnium oxide (HfO_x), that allow an easier trap filling in the semiconductor and the use of low operation voltage. However, in the case of HfO_x, a high temperature usually is needed to induce a uniform and condensed film, which limits its applications in flexible electronics. This paper describes how to obtain HfO_x dielectric thin films and the effect of their implementation in multilayer dielectrics (MLD) at low temperatures (150 °C) to apply in thin film transistors (TFTs) using the combination of solution combustion synthesis (SCS) and ultraviolet (UV) treatment. The single layers and multilayers did not show any trace of residual organics and exhibited a small surface roughness (<1.2 nm) and a high breakdown voltage (>2.7 MV·cm^-1). The resulting TFTs presented a high performance at a low operation voltage (<3 V), with high saturation mobility (43.9 ± 1.1 cm²·V^-1·s^-1), a small subthreshold slope (0.066 ± 0.010 V·dec^-1), current ratio of 1 × 10⁶ and a good idle shelf life stability after 2 months. To our knowledge, the results achieved surpass the actual state-of-the-art. Finally, we demonstrated a low-voltage diode-connected inverter using MLD/IGZO TFTs working with a maximum gain of 1 at 2 V.