Dongyoon Khim

Bio: Dongyoon Khim is an academic researcher from Imperial College London. The author has contributed to research in topics: Field-effect transistor & Ambipolar diffusion. The author has an hindex of 33, co-authored 74 publications receiving 3297 citations. Previous affiliations of Dongyoon Khim include Gwangju Institute of Science and Technology & Dongguk University.

Simple bar-coating process for large-area, high-performance organic field-effect transistors and ambipolar complementary integrated circuits.

Abstract: Solution-processed organic semiconductors are of great potential for large-area, inexpensive, lightweight, and fl exible electronic applications. With respect to these materials, tremendous effort has recently been focused on developing several types of organic electronic and optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), organic fi eld-effect transistors (OFETs), and organic memory and sensors, using graphic-art printing methods on fl substrates. [ 1‐5 ] OFETs are a fundamental building block of integrated circuits (ICs) and drivers for active-matrix fl at-panel displays. Accordingly, they are a promising candidate to replace the vacuum-processed amorphous inorganic ICs; this would enable the use of drivers in printed and fl exible radio-frequency identifi cation tags, memories, sensors, and display backplanes. [ 6 , 7 ] To realize high-speed organic printed ICs, the complementary IC geometry, which consists of p- and n-channel transistors, has an advantage over those that comprise unipolar transistors because of reduced transition delays, higher noise immunity, and negligible power consumption in the static state. [ 8 ] In solution-processed devices, p- and n-type active channels have been patterned at resolutions as low as a few micrometers using a variety of printing methods such as inkjet, spray, and gravure printing. [ 9 ] However, these printing processes typically result in device-to-device performance deviations because of diffi culties inherent in controlling the morphology (e.g., roughness and crystallinity) of micrometre-sized deposits. For example, organic semiconductor droplets that are deposited via ink jet onto non-absorbing substrates typically show signifi cant coffee

Printed, Flexible, Organic Nano‐Floating‐Gate Memory: Effects of Metal Nanoparticles and Blocking Dielectrics on Memory Characteristics

Abstract: The effects of using a blocking dielectric layer and metal nanoparticles (NPs) as charge-trapping sites on the characteristics of organic nano-floating-gate memory (NFGM) devices are investigated. High-performance NFGM devices are fabricated using the n-type polymer semiconductor, poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)), and various metal NPs. These NPs are embedded within bilayers of various polymer dielectrics (polystyrene (PS)/poly(4-vinyl phenol) (PVP) and PS/poly(methyl methacrylate) (PMMA)). The P(NDI2OD-T2) organic field-effect transistor (OFET)-based NFGM devices exhibit high electron mobilities (0.4–0.5 cm2 V−1 s−1) and reliable non-volatile memory characteristics, which include a wide memory window (≈52 V), a high on/off-current ratio (Ion/Ioff ≈ 105), and a long extrapolated retention time (>107 s), depending on the choice of the blocking dielectric (PVP or PMMA) and the metal (Au, Ag, Cu, or Al) NPs. The best memory characteristics are achieved in the ones fabricated using PMMA and Au or Ag NPs. The NFGM devices with PMMA and spatially well-distributed Cu NPs show quasi-permanent retention characteristics. An inkjet-printed flexible P(NDI2OD-T2) 256-bit transistor memory array (16 × 16 transistors) with Au-NPs on a polyethylene naphthalate substrate is also fabricated. These memory devices in array exhibit a high Ion/Ioff (≈104 ± 0.85), wide memory window (≈43.5 V ± 8.3 V), and a high degree of reliability.

Remarkable enhancement of hole transport in top-gated N-type polymer field-effect transistors by a high-k dielectric for ambipolar electronic circuits.

Abstract: A remarkable enhancement of p-channel properties is achieved in initially n-channel dominant ambipolar P(NDI2OD-T2) organic field-effect transistors (OFETs) by the use of the fluorinated high-k dielectric P(VDF-TrFE). An almost two orders of magnitude increase in hole mobility (~0.11 cm(2) V(-1) s(-1) ) originates from a strong interface modification at the semiconductor/dielectric interface, which provides high-performance complementary-like inverters and ring oscillator circuits.

High-Performance Top-Gated Organic Field-Effect Transistor Memory using Electrets for Monolithic Printed Flexible NAND Flash Memory

Abstract: High-performance top-gated organic fi eld-effect transistor (OFET) memory devices using electrets and their applications to flprinted organic NAND fl ash are reported. The OFETs based on an inkjet-printed p-type polymer semiconductor with effi ciently chargeable dielectric poly(2-vinylnaphthalene) (PVN) and high-k blocking gate dielectric poly(vinylidenefl trifl uoroethylene) (P(VDF-TrFE)) shows excellent non-volatile memory characteristics. The superior memory characteristics originate mainly from reversible charge trapping and detrapping in the PVN electret layer effi ciently in low-k/high-k bilayered dielectrics. A strategy is devised for the successful development of monolithically inkjet-printed fl exible organic NAND fl ash memory through the proper selection of the polymer electrets (PVN or PS), where PVN/- and PS/P(VDF-TrFE) devices are used as non-volatile memory cells and ground- and bit-line select transistors, respectively. Electrical simulations reveal that the fl exible printed organic NAND fl ash can be possible to program, read, and erase all memory cells in the memory array repeatedly without affecting the non-selected memory cells.

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors

Abstract: A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications†

Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.

An ultra-lightweight design for imperceptible plastic electronics

Abstract: Electronic devices have advanced from their heavy, bulky origins to become smart, mobile appliances. Nevertheless, they remain rigid, which precludes their intimate integration into everyday life. Flexible, textile and stretchable electronics are emerging research areas and may yield mainstream technologies. Rollable and unbreakable backplanes with amorphous silicon field-effect transistors on steel substrates only 3 μm thick have been demonstrated. On polymer substrates, bending radii of 0.1 mm have been achieved in flexible electronic devices. Concurrently, the need for compliant electronics that can not only be flexed but also conform to three-dimensional shapes has emerged. Approaches include the transfer of ultrathin polyimide layers encapsulating silicon CMOS circuits onto pre-stretched elastomers, the use of conductive elastomers integrated with organic field-effect transistors (OFETs) on polyimide islands, and fabrication of OFETs and gold interconnects on elastic substrates to realize pressure, temperature and optical sensors. Here we present a platform that makes electronics both virtually unbreakable and imperceptible. Fabricated directly on ultrathin (1 μm) polymer foils, our electronic circuits are light (3 g m(-2)) and ultraflexible and conform to their ambient, dynamic environment. Organic transistors with an ultra-dense oxide gate dielectric a few nanometres thick formed at room temperature enable sophisticated large-area electronic foils with unprecedented mechanical and environmental stability: they withstand repeated bending to radii of 5 μm and less, can be crumpled like paper, accommodate stretching up to 230% on prestrained elastomers, and can be operated at high temperatures and in aqueous environments. Because manufacturing costs of organic electronics are potentially low, imperceptible electronic foils may be as common in the future as plastic wrap is today. Applications include matrix-addressed tactile sensor foils for health care and monitoring, thin-film heaters, temperature and infrared sensors, displays, and organic solar cells.

Biomimetic super-lyophobic and super-lyophilic materials applied for oil/water separation: a new strategy beyond nature

Abstract: Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.