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201 results on '"Chang, Ki Soo"'

60. Functional Design of Dielectric–Metal–Dielectric-Based Thin-Film Encapsulation with Heat Transfer and Flexibility for Flexible Displays

Author

Kwon, Jeong Hyun, Choi, Seungyeop, Jeon, Yongmin, Kim, Hyuncheol, Chang, Ki Soo, and Choi, Kyung Cheol

Abstract

In this study, a new and efficient dielectric–metal–dielectric-based thin-film encapsulation (DMD-TFE) with an inserted Ag thin film is proposed to guarantee the reliability of flexible displays by improving the barrier properties, mechanical flexibility, and heat dissipation, which are considered to be essential requirements for organic light-emitting diode (OLED) encapsulation. The DMD-TFE, which is composed of Al2O3, Ag, and a silica nanoparticle-embedded sol–gel hybrid nanocomposite, shows a water vapor transmission rate of 8.70 × 10–6g/m2/day and good mechanical reliability at a bending radius of 30 mm, corresponding to 0.41% strain for 1000 bending cycles. The electrical performance of a thin-film encapsulated phosphorescent organic light-emitting diode (PHOLED) was identical to that of a glass-lid encapsulated PHOLED. The operational lifetimes of the thin-film encapsulated and glass-lid encapsulated PHOLEDs are 832 and 754 h, respectively. After 80 days, the thin-film encapsulated PHOLED did not show performance degradation or dark spots on the cell image in a shelf-lifetime test. Finally, the difference in lifetime of the OLED devices in relation to the presence and thickness of a Ag film was analyzed by applying various TFE structures to fluorescent organic light-emitting diodes (FOLEDs) that could generate high amounts of heat. To demonstrate the difference in heat dissipation effect among the TFE structures, the saturated temperatures of the encapsulated FOLEDs were measured from the back side surface of the glass substrate, and were found to be 67.78, 65.12, 60.44, and 39.67 °C after all encapsulated FOLEDs were operated at an initial luminance of 10 000 cd/m2for sufficient heat generation. Furthermore, the operational lifetime tests of the encapsulated FOLED devices showed results that were consistent with the measurements of real-time temperature profiles taken with an infrared camera. A multifunctional hybrid thin-film encapsulation based on a dielectric–metal–dielectric structure was thus effectively designed considering the transmittance, gas-permeation barrier properties, flexibility, and heat dissipation effect by exploiting the advantages of each separate layer.

Published
2024
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67. High speed parallel spectral-domain OCTusing spectrally encoded line-field illumination.

Author

Lee, Kye-Sung, Hur, Hwan, Bae, Ji Yong, Kim, I Jong, Kim, Dong Uk, Nam, Ki-Hwan, Kim, Geon-Hee, and Chang, Ki Soo

Subjects
OPTICAL coherence tomography, SPECTRUM analysis, DATA encryption, GAUSSIAN beams, CONVEX lenses
Abstract

We report parallel spectral-domain optical coherence tomography (OCT) at 500 000 A-scan/s. This is the highest-speed spectral-domain (SD) OCT system using a single line camera. Spectrally encoded line-field scanning is proposed to increase the imaging speed in SD-OCT effectively, and the tradeoff between speed, depth range, and sensitivity is demonstrated. We show that three imaging modes of 125k, 250k, and 500k A-scan/s can be simply switched according to the sample to be imaged considering the depth range and sensitivity. To demonstrate the biological imaging performance of the high-speed imaging modes of the spectrally encoded line-field OCT system, human skin and a whole leaf were imaged at the speed of 250k and 500k A-scan/s, respectively. In addition, there is no sensitivity dependence in the B-scan direction, which is implicit in line-field parallel OCT using line focusing of a Gaussian beam with a cylindrical lens. [ABSTRACT FROM AUTHOR]

Published
2018
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83. Sustainable Method for the Large-Scale Preparation of Fe3O4 Nanocrystals.

Author

Lee, SungWoo, Yoon, Jae‐Sik, Kang, Sungkyoung, Kwon, Kihyun, Chang, Ki Soo, Lee, SangGap, Choi, Sang‐Il, Jeong, Jong‐Ryul, Lee, Gaehang, Nam, Ki Min, and Davies, P.

Subjects
NANOCRYSTAL synthesis, IRON oxides, DECANOL, THERMAL analysis, CHEMICAL decomposition, POROUS materials
Abstract

In this work, a facile synthetic process is reported for the large-scale synthesis of Fe3O4 nanocrystals. Thermal decomposition of Fe(acac)3 (100 g) in 1-hexadecanol produced Fe3O4 nanocrystals with well-controlled sizes and morphologies. The nanocrystals were spherically shaped with average diameters of 7.8 ± 0.6, 6.5 ± 0.4, and 5.9 ± 0.2 nm when prepared at 300°C, 270°C, and 250°C, respectively. Mechanisms of crystal formation were elucidated on the basis of gas chromatography-mass spectroscopy analysis, enabling the large-scale preparation of Fe3O4 nanocrystals. To provide an environmentally benign route, Fe3O4 nanocrystals were prepared with recycled solvent which was recovered from the initial experiment. The resulting porous Fe3O4 nanocrystals had larger average sizes than those of the initial nanocrystals. Structural characterization was performed using transmission electron microscopy and powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

Published
2016
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84. Heat Transferable Thin Film Encapsulation Inserted Ag Thin Film to Improve Reliability of Flexible Displays.

Author

Kwon, Jeong Hyun, Im, Hyeon-Gyun, Bae, Byeong-Soo, Chang, Ki Soo, Park, Sang-Hee Ko, and Choi, Kyung Cheol

Subjects
HEAT transfer, METALLIC thin films, FLEXIBLE display systems
Abstract

In this study, thin film encapsulation (TFE) with an Ag thin film is proposed to improve the long-term reliability of flexible displays in terms of the barrier property, flexibility, and heat dissipation. By applying thin film encapsulation to bottom-emission organic light-emitting diodes (BEOLEDs) fabricated on glass, the lifetimes of OLED devices were improved, showing differences among TFE layers. The maximum temperatures measured from the backside of the glass substrate were 66.73, 64.15, 59.21 and 39.63 °C after the OLED was operated at a luminance of 10000 cd/m2, and an operational lifetime test results were remarkably consistent with the measurement results of infrared images. Efficient heat dissipation through thermally conductive TFE layers improved the OLED reliability in terms of lifetime. [ABSTRACT FROM AUTHOR]

Published
2016
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100. Correlation between frictional heat and triboelectric charge: In operandotemperature measurement during metal-polymer physical contact

Author

Lee, Dong Woo, Kong, Dae Sol, Kim, Jong Hun, Park, Sang Hyeok, Hu, Ying Chieh, Ko, Young Joon, Jeong, Chan Bae, Lee, Seoku, Il Jake Choi, Joong, Lee, Gwan-Hyoung, Lee, Minbaek, Wie, Jeong Jae, Chang, Ki Soo, Park, Jeong Young, and Jung, Jong Hoon

Abstract

In operandotechniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operandotemperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operandotemperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.

Published
2022
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