Strategy for Selective Printing of Gate Insulators Customized for Practical Application in Organic Integrated Devices

High-k organic-inorganic hybrid dielectric material for flexible thin-film transistors and printed logic circuits

A new photopolymerizable organic-inorganic (O-I) hybrid sol-gel material, AUP@SiOx-184, has been synthesized and utilized as a gate dielectric in flexible organic thin-film transistors (OTFTs). The previously reported three-arm alkoxy-functionalized silane amphiphilic polymer has yielded stable O-I hybrid materials comprising uniformly dispersed nanoparticles in the sol state. In this study, a photosensitizer was introduced, facilitating curing effects under ultraviolet light. Photo-crosslinking enhances the stability of hydroxyl radicals within inorganic nanoparticles, thereby minimizing device hysteresis. This approach also contributes to achieving a low leakage current and a high dielectric constant (high-k) while maintaining reduced thickness. Moreover, AUP@SiOx-184 films are amenable to patterning through UV photopolymerization and can be successfully produced using printing techniques. Compared to other materials, they exhibit outstanding flexibility and improved insulating capabilities. Additionally, OTFTs incorporating AUP@SiOx-184 layers demonstrate extremely stable driving features on flexible substrates. Selective printing and specific patterning play crucial roles in the fabrication of logic circuits. This synthesis strategy has resulted in integrated logic devices that have successfully demonstrated their functionality, highlighting its value for producing functional O-I hybrid materials. Utilizing AUP@SiOx-184 as a gate dielectric in OTFTs showcases its potential to advance electronic technologies that are both flexible and high-performing.

Surface engineering of high-k polymeric dielectric layers with a fluorinated organic crosslinker for use in flexible-platform electronics

High-k polymeric layers were prepared by combining various functional groups and were applied as gate dielectrics for practical organic field-effect transistors (OFETs). Crosslinking of the polymeric layers through UV-assisted organic azide fluorine-based crosslinkers induced dramatic improvements in the electrical performance of the OFET, such as field-effect mobility and bias-stress stability. Our synthesis and manufacturing method can be a useful technique for ensuring device operation stability and electrical property enhancement. With this analysis, we further applied our polymer-dielectric OFETs to flexible-platform-based electronic components, including unit OFETs and simple logic devices (NOT, NAND, and NOR gates). The outcomes of this research and development suggest a suitable method for the low-cost mass production of large-area flexible and printable devices, using a printing-based approach to replace current processes.

Amorphous Fluorinated Acrylate Polymer Dielectrics for Flexible Transistors and Logic Gates with High Operational Stability

Fluorinated amorphous polymeric gate-insulating materials for organic thin-film transistors (OTFTs) not only form hydrophobic surfaces but also significantly reduce traps at the interface between the organic semiconductor and gate insulator. Therefore, these polymeric materials can enhance the OTFT's operation stability. In this study, we synthesized a new polymeric insulating material series composed of acrylate and fluorinated functional groups (with different ratios) named MBHCa-F and used them as gate insulators for OTFTs and in other applications. The insulating features of the MBHCa-F polymers, including surface energy, surface atomic content properties, dielectric constant, and leakage current, were clearly analyzed with respect to the content of the fluorinated functional groups. At higher fluorine-based functional group content, the polymeric series exhibited higher fluorine-based contents at the surface and superior electrical properties, such as field-effect mobility and driving stability, at OTFTs. Therefore, we believe that this study provides a substantial method for synthesizing polymeric insulating materials to enhance the operational stability and electrical performance of OTFTs.

Physical Properties of an Ultrathin Al2O3/HfO2 Composite Film by Atomic Layer Deposition and the Application in Thin-Film Transistors

A high-quality ultrathin dielectric film is important in the field of microelectronics. We designed a composite structure composed of Al₂O₃/HfO₂ with different Al₂O₃/HfO₂ cycles prepared by atomic layer deposition (ALD) to obtain high-quality ultrathin (1-12 nm) dielectric films. Al₂O₃ protected HfO₂ from interacting with the Si substrate and inhibited the crystallization of the HfO₂ film. High permittivity material of HfO₂ was adopted to guarantee the good insulating property of the composite film. We investigated the physical properties as well as the growth mode of the composite film and found that the film exhibited a layer growth mode. The water contact angle and grazing-incidence small-angle X-ray scattering analyses revealed that the film was formed physically at 3 nm, while the thickness of the electrically stable film was 10 nm from grazing-incidence wide-angle X-ray scattering and dielectric constant analyses. The composite film was applied as a dielectric layer in thin-film transistors (TFTs). The threshold voltage was decreased to 0.27 V compared to the organic field-effect transistor with the single HfO₂ dielectric, and the subthreshold swing was as small as 0.05 V/dec with a carrier mobility of 49.2 cm²/V s. The off-current was as low as 10^-11 A, and the on/off ratio was as high as 5.5 × 10⁶. This ALD-prepared composite strategy provides a simple and practical way to obtain the high-quality dielectric film, which shows the potential application in the field of microelectronics.

Recent Progress in Thin-Film Transistors toward Digital, Analog, and Functional Circuits

Thin-film transistors have been extensively developed due to their process merit: high compatibility with various substrates, large-area processes, and low-cost processes. Despite these advantages, most efforts for thin-film transistors still remain at the level of unit devices, so the circuit level for practical use needs to be further developed. In this regard, this review revisits digital and analog thin-film circuits using carbon nanotubes (CNTs), organic electrochemical transistors (OECTs), organic semiconductors, metal oxides, and two-dimensional materials. This review also discusses how to integrate thin-film circuits at the unit device level and some key issues such as metal routing and interconnection. Challenges and opportunities are also discussed to pave the way for developing thin-film circuits and their practical applications.

Artificial Tactile Recognition Enabled by Flexible Low-Voltage Organic Transistors and Low-Power Synaptic Electronics

The advancement of self-powered intelligent strain systems for human-computer interaction is crucial toward wearable and energy-saving applications. Simultaneously, lowering operating voltage and thus reducing power consumption are of particular interests. A brain-like smart synaptic hardware system is considered as a promising candidate for low-power, parallel computing and learning processes. However, the combination of low-voltage organic transistors and energy efficient smart synapse hardware systems driven by a tactile signal has been hindered by the limited materials and technology. Here, by employing an elastomeric copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with a high HFP content of 25 mol %, flexible, low-voltage transistors (|V_G| ≤ 3 V) and a low energy consumption synapse ≤ 9.2 × 10^-17 J are devised simultaneously, along with the lowest quality factor (R = P_w × V_G, 2.76 × 10^-16 J V). Furthermore, based on the low voltage and low power consumption characteristics, flexible artificial tactile recognition system and Morse code recognition are established without any computing supporting. Mechanical flexibility, cycling stability, image contrast enhancement functions, and simulated pattern recognition accuracy of the multilayer perceptron neural network are also simulated. This work recommends a route of exploiting low voltage, low power consumption synaptic systems and smart human-machine interfaces with low energy loss based on flexible organic synaptic transistors.

Electrohydrodynamic-Jet-Printed Phthalimide-Derived Conjugated Polymers for Organic Field-Effect Transistors and Logic Gates

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.

Mass-Synthesized Solution-Processable Polyimide Gate Dielectrics for Electrically Stable Operating OFETs and Integrated Circuits

Polyimides (PIs) are widely utilized polymeric materials for high-temperature plastics, adhesives, dielectrics, nonlinear optical materials, flexible hard-coating films, and substrates for flexible electronics. PIs can be facilely mass-produced through factory methods, so the industrial application value is limitless. Herein, we synthesized a typical poly(amic acid) (PAA) precursor-based solution through an industrialized reactor for mass production and applied the prepared solution to form thin films of PI using thermal imidization. The deposited PI thin films were successfully applied as gate dielectrics for organic field-effect transistors (OFETs). The PI layers showed suitable characteristics for dielectrics, such as a smooth surface, low leakage current density, uniform dielectric constant (k) values regardless of frequency, and compatibility with organic semiconductors. Utilizing this PI layer, we were able to fabricate electrically stable operated OFETs, which exhibited a threshold voltage shift lower than 1 V under bias-stress conditions and a field-effect mobility of 4.29 cm² V^-1 s^-1. Moreover, integrated logic gates were manufactured using these well-operated OFETs and displayed suitable operation behavior.

Electrohydrodynamic-Jet-Printed Cinnamate-Fluorinated Cross-Linked Polymeric Dielectrics for Flexible and Electrically Stable Operating Organic Thin-Film Transistors and Integrated Devices

Herein, printable polymer series containing different portions of cinnamate and perfluorinated phenyl functionalities, namely, polyperfluorostyrene-co-poly(vinylbenzyl cinnamates) (PFS-co-PVBCi (x:y)) copolymers, were synthesized and applied as gate dielectrics for organic thin-film transistors (OTFTs). The polymeric dielectrics were successfully printed via electrostatic force-assisted dispensing mode of electrohydrodynamic jet printing. The dielectric characteristics of the printed polymers, such as surface energy, dielectric constant, leakage current, atomic depth profiles, and deposited semiconducting layer characteristics, were clearly identified. In particular, the difference in driving stability of OTFTs according to the type of polymer was analyzed in detail and a possible mechanism was proposed. Results suggested that PFS-co-PVBCi (3:7) led to optimized consequences, yielding an almost negligible V_th shift under continuous bias stress. Through this, we successfully implemented flexible OTFT and logic devices using printed PFS-co-PVBCi (3:7) dielectrics with stable operation properties. Therefore, we believe that this study will facilitate the printing and synthesis of polymer dielectrics to produce printed and flexible OTFTs.