Yong-Hoon Kim

Bio: Yong-Hoon Kim is an academic researcher from Sungkyunkwan University. The author has contributed to research in topics: Thin-film transistor & Oxide. The author has an hindex of 32, co-authored 166 publications receiving 4874 citations. Previous affiliations of Yong-Hoon Kim include Soongsil University & Korea Institute of Science and Technology.

Flexible metal-oxide devices made by room-temperature photochemical activation of sol–gel films

Abstract: A method for annealing metal-oxide semiconductor films with deep-ultraviolet light yields thin-film transistors with performance comparable to that of thermally annealed devices, and widens the range of substrates on which such devices can be fabricated. Solution-processable metal-oxide semiconductors are attractive materials for low-cost, flexible electronics, but the need to anneal the deposited materials at relatively high temperatures limits the range of substrates on which such devices can be fabricated. Now Yong-Hoon Kim and colleagues demonstrate that irradiating the solution-cast films with deep ultraviolet light can obviate the need for an annealing step. In this system, photochemical activation serves essentially the same purpose as annealing, and the resulting semiconducting materials have device performance levels comparable to those produced using the high-temperature techniques. Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors1,2,3,4,5,6,7. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates8,9,10,11,12,13. But metal-oxide formation by the sol–gel route requires an annealing step at relatively high temperature2,14,15,16,17,18,19, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol–gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm2 V−1 s−1 (with an Al2O3 gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.

Enhancement of field-effect mobility due to surface-mediated molecular ordering in regioregular polythiophene thin film transistors

Abstract: With the aim of enhancing the field-effect mobility by promoting surface-mediated two-dimensional molecular ordering in self-aligned regioregular poly(3-hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (–NH2, –OH, and –CH3). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field-effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm2 V–1 s–1. This surprising increase in field-effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the π–H interactions between the thienyl-backbone bearing π-systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.

Recent Progress of Textile-Based Wearable Electronics: A Comprehensive Review of Materials, Devices, and Applications.

Abstract: Wearable electronics are emerging as a platform for next-generation, human-friendly, electronic devices. A new class of devices with various functionality and amenability for the human body is essential. These new conceptual devices are likely to be a set of various functional devices such as displays, sensors, batteries, etc., which have quite different working conditions, on or in the human body. In these aspects, electronic textiles seem to be a highly suitable possibility, due to the unique characteristics of textiles such as being light weight and flexible and their inherent warmth and the property to conform. Therefore, e-textiles have evolved into fiber-based electronic apparel or body attachable types in order to foster significant industrialization of the key components with adaptable formats. Although the advances are noteworthy, their electrical performance and device features are still unsatisfactory for consumer level e-textile systems. To solve these issues, innovative structural and material designs, and novel processing technologies have been introduced into e-textile systems. Recently reported and significantly developed functional materials and devices are summarized, including their enhanced optoelectrical and mechanical properties. Furthermore, the remaining challenges are discussed, and effective strategies to facilitate the full realization of e-textile systems are suggested.

High-mobility organic transistors based on single-crystalline microribbons of triisopropylsilylethynyl pentacene via solution-phase self-assembly

Abstract: There has been significant interest in the fabrication of 1D single-crystalline building blocks from p-conjugated organic molecules for use in high-performance supramolecular electronics. Control over the single-crystalline supramolecular self-assembly of p-conjugated organic molecules provides great opportunities to fine-tune the molecular ordering of 1D nanoor microstructured building blocks grown by strong p–p interactions, and thus to optimize their electrical properties for applications in organic field-effect transistors (OFETs). Obtaining high-quality single crystals with p-conjugated organic molecules through solution processing is required more than obtaining them through complex vacuum processes. Some research has recently shown that self-assembly through strong p–p stacking is an effective approach to producing well-defined single-crystalline nanoor microstructures for p-conjugated organic molecules in the solution phase. Among p-conjugated organic materials, pentacene, a fused-ring polycyclic aromatic hydrocarbon, is regarded as one of the most promising materials for use in organic electronics, because of its excellent semiconducting behavior, which is comparable to that of hydrogenated amorphous silicon (a-Si:H). However, the structural analysis of p-conjugated organic materials such as acenes has shown that their crystal structures adopt the so-called “herringbone” motif in which the molecules are packed more or less edge-to-face in 2D layers. However, this edge-to-face packing minimizes the p-overlap between adjacent molecules, resulting in relatively low mobilities. It has been suggested that it might be possible to achieve higher mobilities by designing p-conjugated molecules that stack face-to-face (p-stacking) in the solid state, thus increasing the intermolecular interactions. In other words, a cofacial p-stacked structure is expected to provide more efficient p-orbital overlap, thereby facilitating charge transport. Simulations have shown that halogen groups promote p-stacking and that one or more substitutions of relatively bulky groups into the peripositions of the polyacenes disrupts the herringbone structure of these compounds. In this study, therefore, the properties of triisopropylsilylethynyl pentacene (TIPS-PEN) were investigated, as suggested by Anthony and co-workers, because of its solution processability, significantly greater p-orbital overlap, and lower interplanar spacing, than unsubstituted pentacene. Some previous research has focused on the fabrication of thin films and bulk materials using TIPS-PEN molecules, however, the 1D self-assembled single-crystalline nanoor microstructures (i.e., the intermediate state between free molecules and bulk materials) of TIPS-PEN molecules have not yet been studied. In this study, 1D single-crystalline microribbons of TIPS-PEN with structural perfectness comparable to that of inorganic single crystals were easily prepared by using the specific-solvent-exchange method in the solution phase, and OFETs based on individual microribbons with hitherto unreported high performance were fabricated. The TIPS-PEN microribbons were prepared from TIPSPEN powder as the starting material by using the solvent-exchange method in the solution phase (for details, see the Experimental section). The conformational flexibility of the triisopropylsilyl side group of the TIPS-PEN molecule (Fig. 1) gives it sufficient solubility in hydrophobic solvents such as toluene, and the increased density of the bulky groups enables the tight packing of the pentacene backbones to maximize the p–p interactions. As a result, the TIPS-PEN molecule becomes insoluble in more polar solvents such as acetonitrile. As shown in Figure 1B, the injection of a minimum volume of concentrated toluene solution of TIPS-PEN into acetonitrile led to the formation of nanocrystals through self-assembly and the growth of a microribbon in the closed chamber (Fig. 1C). Figure S1 (Supporting Information) shows the C O M M U N IC A TI O N

Brain-Inspired Photonic Neuromorphic Devices using Photodynamic Amorphous Oxide Semiconductors and their Persistent Photoconductivity

Abstract: The combination of a neuromorphic architecture and photonic computing may open up a new era for computational systems owing to the possibility of attaining high bandwidths and the low-computation-power requirements. Here, the demonstration of photonic neuromorphic devices based on amorphous oxide semiconductors (AOSs) that mimic major synaptic functions, such as short-term memory/long-term memory, spike-timing-dependent plasticity, and neural facilitation, is reported. The synaptic functions are successfully emulated using the inherent persistent photoconductivity (PPC) characteristic of AOSs. Systematic analysis of the dynamics of photogenerated carriers for various AOSs is carried out to understand the fundamental mechanisms underlying the photoinduced carrier-generation and relaxation behaviors, and to search for a proper channel material for photonic neuromorphic devices. It is found that the activation energy for the neutralization of ionized oxygen vacancies has a significant influence on the photocarrier-generation and time-variant recovery behaviors of AOSs, affecting the PPC behavior.

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

Abstract: Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

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.

The larger acenes: versatile organic semiconductors.

Abstract: Acenes have long been the subject of intense study because of the unique electronic properties associated with their pi-bond topology. Recent reports of impressive semiconductor properties of larger homologues have reinvigorated research in this field, leading to new methods for their synthesis, functionalization, and purification, as well as for fabricating organic electronic components. Studies performed on high-purity acene single crystals revealed their intrinsic electronic properties and provide useful benchmarks for thin film device research. New approaches to add functionality were developed to improve the processability of these materials in solution. These new functionalization strategies have recently allowed the synthesis of acenes larger than pentacene, which have hitherto been largely unavailable and poorly studied, as well as investigation of their associated structure/property relationships.