• Journal of Welding and Joining
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• v.32 no.3
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• pp.34-42
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• 2014

Flexible devices have been developed from their rigid, heavy origins to become bendable, stretchable and portable. Such a paper displays, e-skin, textile electronics are emerging research areas and became a mainstream of overall industry. Thin film transistors, diodes and sensors built on plastic sheets, textile and other unconventional substrates have a potential applications in wearable displays, biomedical devices and electronic system. In this review, we describe current trends in technologies for flexible/wearable electronics.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.30.2-30.2
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• 2010

Nano-scale p-n junction can generate various nano-scale functional devices such as nanowire light emitting diode, nanowire solar cell, and nanowire sensor. The core shell type nanowire p-n junction has been considered for the high efficient devices in many previous reports. On the other hand, although device efficiency is relatively lower, the cross bar type p-n junction has simple topological structure, suggested by C.M. Lieber group, to integrate easily many p-n junction devices in one board. In this study, for the integration of the cross bar nanowire p-n junction device, a simple fabrication route, employed dielectrophoretic array and direct printing techniques, was demonstrated by the successful fabrication and programmable integration of the nanowire cross bar p-n junction solar cell. This direct printing process will give the single nanowire solar cell the opportunity of the integration on the circuit board with other nanowire functional devices.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.59.1-59.1
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• 2012

Organic thin-film transistors (OTFTs) with printable semiconductors are promising candidate devices for flexible active-matrix (AM) display applications. Yet, stable operation of actual display panels driven by OTFTs has seldom been reported up to date. Here, we demonstrate a flexible reflective type polymer dispersed liquid crystal (PDLC) display, in which inkjet-printed OTFT arrays are used as driving elements with excellent areal uniformity in terms of device performance. As the active semiconductor, a novel, ambient processable conjugated copolymer was synthesized. The stability of the devices with respect to electrical bias stress was improved by applying a channel-passivation layer, which suppresses the environmental effects and hence reduces the density of trap states at the channel/dielectric interface. The combination of high performance and high stability OTFT devices enabled the successful realization of stable operating flexible color-displays by inkjet-printing.

• Current Optics and Photonics
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• v.3 no.1
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• pp.66-71
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• 2019

Application of liquid crystal (LC) materials to a flexible device is challenging because the bending of LC displays easily causes change in thickness of the LC layer and orientation of LCs, resulting in deterioration in a displayed image quality. In this work, we demonstrate a prototype device combining a flexible polymer substrate and an optically isotropic LC-polymer composite in which the device consists of interdigitated in-plane switching electrodes deposited on a flexible colorless polyimide substrate and the composite consisting of nano-sized LC droplets in a polymer matrix. The device can keep good electro-optic characteristics even when it is in a bending state because the LC orientation is not disturbed in both voltage-off and -on states. The proposed device shows a high potential to be applicable for future flexible LC devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.232.1-232.1
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• 2014

The green displays are the human friendly displays, the nature friendly displays, and the economical displays. Electrochromic displays are low cost and environmental devices because they do have more choice of colours and use much less power. The elements of the electrochromic devices consist of at least two conductors, an electrochromic material and an electrolyte. The optical properties were obtained using the optical contrast between the transparency of the substrate and the coloured state of the electrochromic materials. These devices can be fully flexible and printable. Due to the characteristics of the high coloration efficiency and memory effects, the electrochromic devices have been used in various applications such as information displays, smart windows, light shutters and electronic papers. Among these technical fields switchable mirrors have been received much attention in the applicative point of view of various electronic devices production. We have developed a novel silver (Ag) deposition-based electrochromic device for the reversible electrodeposition (RED) system. The electrochromic device can switch between transparent states and mirror states in response to a change in the applied voltage. The dynamic range of transmittance percent (%) for the fabricated device is about 90% at 550 nm wavelength. Also, we successfully fabricated the large area RED display system using the parted electrochromic cells of the honey comb structure.

• Bulletin of the Korean Chemical Society
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• v.35 no.11
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• pp.3299-3302
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• 2014

The In2S3 thin films of tetragonal structure and In2O3 films of cubic structure were synthesized by a spin coating method from the organometallic compound precursor triethylammonium indium thioacetate ($[(Et)_3NH]^+[In(SCOCH_3)_4]^-$; TEA-InTAA). In order to determine the electron mobility of the spin-coated TEA-InTAA films, thin film transistors (TFTs) with an inverted structure using a gate dielectric of thermal oxide ($SiO_2$) was fabricated. These devices exhibited n-channel TFT characteristics with a field-effect electron mobility of $10.1cm^2V^{-1}s^{-1}$ at a curing temperature of $500^{\circ}C$, indicating that the semiconducting thin film material is applicable for use in low-cost, solution-processed printable electronics.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.58.1-58.1
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• 2012

Direct write technologies provide flexible and economic means to manufacture low-cost large-area electronics. In this regard inkjet printing has frequently been used for the fabrication of electronic devices. Full advantage of this method, which is capable of reliable direct patterning with line and space dimensions in the 10 to 100 um regime, is only made with all-solution based processing. Among these printable electronic materials, silver and copper nanoparticles have been used as interconnecting materials. Specially, solutions of organic-encapsulated silver and copper nanoparticles may be printed and subsequently annealed to form low-resistance conductor patterns. In this talk, we describe novel processes for forming silver nanoplates and copper ion complex which have unique properties, and discuss the optimization of the printing/annealing processes to demonstrate plastic-compatible low-resistance conductors. By optimizing both the interconnecting materials and the surface treatments of substrate, it is possible to produce particles that anneal at low-temperatures (< $200^{\circ}C$) to form continuous films having low resistivity and appropriate work function for formation of rectifying contacts.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.29-29
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• 2008

Realization of electronics with performance equal to established technologies that use rigid semiconductor wafers, but in lightweight, foldable and stretchable formats would enable many new application possibilities. Examples include wearable systems for personal health monitoring, 'smart' surgical gloves with integrated electronics and electronic eye type imagers that incorporate focal plane arrays on hemispherical substrates. Circuits that use organic or certain classes of inorganic electronic materials on plastic or steel foil substrates can provide some degree of mechanical flexibility, but they cannot be folded or stretched. Also, with few exceptions such systems offer only modest electrical performance. In this talk, I will present a new approach to high performance, flexible and stretchable integrated circuits. These systems combine single-crystal silicon nanoribbons with thin plastic or elastomeric substrates using both "top-down" and "transfer-printing" technologies. The strategies represent promising routes to high performance, flexible and stretchable optoelectronic devices that can incorporate established, high performance inorganic electronic materials.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.691-692
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• 2009

Screen printable CNT pastes were formulated including conductive nano particles (CNPs) and their properties were investigated with an expectation of stable cold cathodes for advanced lamp application. CNT cathodes showed a turn-on field of 1~1.5V/um, a life time of ~100 hours at an emission current density of 10uA/$cm^2$ for DC-bias. Detailed analysis of measured I-V was carried out by applying Fowler-Nordheim model to trace down the origin of emission property degradation.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.3.2-3.2
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• 2009

Development of printed electronics, which is occasionally referred to as 'flexible' or 'polymer' electronics, has attracted considerable world wide attention in recent years. Printed (or flexible) electronics is currently expected to represent a new form of electronics and open up wide ranging applications in displays, electron devices for medical use, sensors, and other areas. This presentation aims to provide a strategy for scalable and viable paths to accomplish flexible, printable, large area circuits displaying high performance. Novel approaches evolving from system on package (SoP) to system on flex (SoF) technology will allow the integration of heterogeneous materials platforms into a system which is needed to enhance the functionality of the system. The talk also includes speculations about areas on which future advances in printed electronics could have a substantial impact along with a brief introduction of the Korea Printed Electronics Association (KoPEA).