9 research outputs found

    Effect of Back-Channel Surface on Reliability of Solution-Processed In<sub>0.51</sub>Ga<sub>0.15</sub>Zn<sub>0.34</sub>O Thin-Film Transistors with Thin Active Layer

    No full text
    We have investigated the degradation mechanism of solution-processed indium–gallium–zinc-oxide (IGZO) thin-film transistors. The threshold voltage shift (ΔVth) followed a linear function under negative gate bias stress (NBS), while it showed a stretched-exponential behavior under positive gate bias stress. The slope of ΔVth for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) due to the fully depleted active layer under NBS. Therefore, the degradation phenomenon under NBS was related to the adsorption at back-channel surface. The back-channel surface could be affected by the gate bias under NBS, and the molecules adsorbed at the IGZO layer were positively charged and induced extra electrons by NBS. We verified that the number of positively charged adsorbates had a proportional relationship with the ΔVth based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the ΔVth equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface by comparing the ΔVth between different atmospheric conditions and LD. Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices

    Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

    No full text
    We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications

    One-Step Interface Engineering for All-Inkjet-Printed, All-Organic Components in Transparent, Flexible Transistors and Inverters: Polymer Binding

    No full text
    We report a one-step interface engineering methodology which can be used on both polymer electrodes and gate dielectric for all-inkjet-printed, flexible, transparent organic thin-film transistors (OTFTs) and inverters. Dimethyl­chlorosilane-terminated polystyrene (PS) was introduced as a surface modifier to cured poly­(4-vinylphenol) dielectric and poly­(3,4-ethylene­dioxy­thiophene):poly­styrene­sulfonate (PEDOT:PSS) electrodes without any pretreatment. On the untreated and PS interlayer-treated dielectric and electrode surfaces, 6,13-bis­(tri­isopropyl­silyl­ethynyl)­pentacene was printed to fabricate OTFTs and inverters. With the benefit of the PS interlayer, the electrical properties of the OTFTs on a flexible plastic substrate were significantly improved, as shown by a field-effect mobility (μ<sub>FET</sub>) of 0.27 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and an on/off current ratio (<i>I</i><sub>on</sub>/<i>I</i><sub>off</sub>) of greater than 10<sup>6</sup>. In contrast, the untreated systems showed a low μ<sub>FET</sub> of less than 0.02 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> ∼ 10<sup>4</sup>. Additionally, the all-inkjet-printed inverters based on the PS-modified surfaces exhibited a voltage gain of 7.17 V V<sup>–1</sup>. The all-organic-based TFTs and inverters, including deformable and transparent PEDOT:PSS electrodes with a sheet resistance of 160–250 Ω sq<sup>–1</sup>, exhibited a light transmittance of higher than 70% (at wavelength of 550 nm). Specifically, there was no significant degradation in the electrical performance of the interface engineering-assisted system after 1000 bending cycles at a radius of 5 mm

    Nonpatterned Soft Piezoresistive Films with Filamentous Conduction Paths for Mimicking Multiple-Resolution Receptors of Human Skin

    No full text
    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

    Transparent Large-Area MoS<sub>2</sub> Phototransistors with Inkjet-Printed Components on Flexible Platforms

    No full text
    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 (MoS<sub>2</sub>) 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 MoS<sub>2</sub>, 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 MoS<sub>2</sub>, the fully printed MoS<sub>2</sub> phototransistors exhibit excellent transparency and mechanically stable operation

    Silent Speech Recognition with Strain Sensors and Deep Learning Analysis of Directional Facial Muscle Movement

    No full text
    Silent communication based on biosignals from facial muscle requires accurate detection of its directional movement and thus optimally positioning minimum numbers of sensors for higher accuracy of speech recognition with a minimal person-to-person variation. So far, previous approaches based on electromyogram or pressure sensors are ineffective in detecting the directional movement of facial muscles. Therefore, in this study, high-performance strain sensors are used for separately detecting x- and y-axis strain. Directional strain distribution data of facial muscle is obtained by applying three-dimensional digital image correlation. Deep learning analysis is utilized for identifying optimal positions of directional strain sensors. The recognition system with four directional strain sensors conformably attached to the face shows silent vowel recognition with 85.24% accuracy and even 76.95% for completely nonobserved subjects. These results show that detection of the directional strain distribution at the optimal facial points will be the key enabling technology for highly accurate silent speech recognition
    corecore