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159 results on '"Cho, Kwan Hyun"'

14. P‐100: Control of Vacuum Pressure in Vacuum Drying Process for Uniform Film Formation of Inkjet‐Printed OLEDs.

Author

Cho, Kwan Hyun, Noh, Youngwook, Lee, Sang Youn, and Hwang, Jun Young

Subjects
BOILING-points, VACUUM chambers, PRESSURE control, PIXELS, UNIFORMITY, ORGANIC light emitting diodes
Abstract

To enhance the performance of inkjet OLED/QLED devices, achieving a uniform film during the drying process is crucial. This study aims to improve both intra‐pixel and inter‐pixel uniformity in the drying process of inkjet printing technology. We conducted a comprehensive analysis of drying characteristics under various mixed solvent boiling points in nitrogen(N2) conditions. Additionally, during vacuum drying process, we carefully studied the characteristics based on adjustments in vacuum pressure and heating. Our focus was on analyzing the thickness profiles of dried pixel arrays in different positions: top, center, bottom, and left parts. Through the optimization of vacuum drying using solvents with a high boiling point (BP), we successfully achieved uniform film formation within and between pixels in inkjet‐printed pixel arrays. [ABSTRACT FROM AUTHOR]

Published
2024
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21. Controlling the Surface Modification by CF4 Plasma Treatment for Inkjet Printed Color Conversion Layer With InP‐Based QDs Ink.

Author

Lee, Sang Youn, Sakong, Chun, Choi, Sung‐Hwan, Ju, Byeong‐Kwon, and Cho, Kwan Hyun

Subjects
INK, LIGHT emitting diodes, SURFACE energy, QUANTUM dots, HYDROPHOBIC surfaces
Abstract

Controlling of thickness profile in micro‐scale pixels via an inkjet printing process remains a challenge and strict control of surface energy is required. Herein, the surface energy of each substrate is controlled by using CF4 plasma treatment (CPT) to control thickness profile and improve color conversion efficiency (CCE) of the inkjet printed quantum dots (QDs) color conversion layer (CCL). The bank surface becomes hydrophobic due to the fluorination, while the glass becomes hydrophilic due to the cleaning effect by the CPT. Through a systemic investigation of the polar and non‐polar components of the surface energy, it is found that the ink behavior of inkjet‐printed QDs in the pixels is closely related to the non‐polar component of the surface energy. In addition, it is found that more rigorous control of the surface is required for array printing and a wide range of thickness profile control is possible by CPT. The thickness increases by up to 10 µm, the blue leakage is reduced by 26.38%, and the CCE increases by a maximum of 5.71% depending on the CPT. As a result, the relationship between the thickness profile of the CCL and CCE is confirmed through the fabrication of QD‐organic light emitting diodes. [ABSTRACT FROM AUTHOR]

Published
2023
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30. Wall voltage and priming effect due to auxiliary electrode in ac PDP with auxiliary electrode

Author

Cho, Kwan Hyun, Lee, Sung-Min, and Choi, Kyung Cheol

Subjects
Electrodes -- Design and construction, Plasma display systems -- Design and construction, Voltage -- Measurement, Plasma display, Business, Chemistry, Electronics, Electronics and electrical industries
Abstract

Variation of wall voltage and priming effect due to an auxiliary electrode are investigated with the aim of attaining a better understanding of the discharge phenomenon in an ac plasma display panel with an auxiliary electrode. A periodic positive pulse, which is applied to the auxiliary electrode during afterglow, reduced wall charges accumulated on the auxiliary and sustain electrodes so that discharge current decreased with an increase of auxiliary-pulse voltage. In addition, the auxiliary pulse influenced on the priming particles so that the optical output was not changed as much as the reduced current and sustain voltage was lowered. Based on these results, modified auxiliary-pulse waveforms, i.e., dual auxiliary pulses, were applied to the auxiliary electrode to utilize more priming particles to improve luminous efficacy. The proposed auxiliary waveforms improved IR efficiency by 10%-15% as compared to that obtained with a single auxiliary pulse. Index Terms--Auxiliary electrode, detecting pulse, plasma display panel (PDP), priming effect, wall voltage.

Published
2007

39. Low Temperature Deposition of Inorganic Thin Films by Ultraviolet Laser-Assisted Chemical Vapor Deposition

Author

Lee Ho-Nyun, Kang Kyung Tae, Cho Kwan Hyun, J Hwang David, Kuk Seungkuk, Zhang Tao, and Park Jongmin

Subjects
Materials science, Hybrid physical-chemical vapor deposition, Ion plating, 02 engineering and technology, Combustion chemical vapor deposition, 021001 nanoscience & nanotechnology, 01 natural sciences, Electron beam physical vapor deposition, Pulsed laser deposition, 010309 optics, Chemical engineering, Plasma-enhanced chemical vapor deposition, 0103 physical sciences, Deposition (phase transition), General Materials Science, Thin film, 0210 nano-technology
Published
2016

45. Controlling Drying Conditions in Vacuum for Uniform Film Formation in Inkjet-Printed OLEDs

Author

Noh, Youngwook, Hwang, Jun Young, Lee, Sang Youn, and Cho, Kwan Hyun

Abstract

The drying process of inkjet-printed organic light-emitting diodes (OLEDs) is influenced by both ink properties and external environmental factors, which ultimately affect the film profile. First, we conducted a detailed investigation of the drying time based on changes in the boiling point (BP) of mixed solvents and analyzed the correlation with the film profile. Under atmospheric drying conditions in a nitrogen (N2) atmosphere, the increased drying time under capillary-driven flow leads to greater particle movement toward the edges, significantly increasing the coffee-ring effect. Additionally, using a high-boiling-point solvent mixture of ethyl 4-methylbenzoate (EMB) and 2-ethylhexyl benzoate (EHB), we produced uniform thin films both between and within pixels (inter and intrapixel uniformity) through a vacuum drying process. In particular, we proposed a drying process model that divides the drying of inkjet pixels into a microfluidic phase and a gelation phase. Through five gelation phase-controlled vacuum drying experiments, the morphology within the pixels was precisely investigated. By sufficiently removing residual solvents after the microfluidic phase and then proceeding with heating, we produced uniform thin films. Furthermore, we fabricated OLED devices using this gelation phase-controlled vacuum drying process, achieving uniform pixel emission and improved device performance.

Published
2024
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50. Effect of Meniscus Damping Ratio on Drop-on-Demand Electrohydrodynamic Jetting.

Author

Kim, Samuel Haedong, Kang, Heuiseok, Kang, Kyungtae, Lee, Sang Ho, Cho, Kwan Hyun, and Hwang, Jun Young

Subjects
ELECTROHYDRODYNAMICS, ELECTRIC fields, BIOENGINEERING
Abstract

Drop-on-demand (DOD) electrohydrodynamic (EHD) jet printing uses a nozzle and pulsated electric fields to eject small ink droplets of functional material to the appointed spot of a substrate at the appointed time, which offers solutions of high resolution patterning for fabrication of printed electronics, bioengineering, and display. Because the EHD jet connects fine drops to yield a fine pattern, it is essential to realize high throughput by generating drops quickly and reliably. In this study, the characteristics of jetting frequency were experimentally investigated as a function of nozzle dimensions by measuring response of jetting frequency to pulsating frequency which is varying from 1 Hz to 2000 Hz. The results showed that, even when the nozzle diameter is the same, the other dimensions of the nozzle significantly change the response of jetting to high pulsating frequency. Using a linear damping model describing hydrodynamic motion of ink inside the nozzle, the different behavior of the jetting frequency was explained via the different damping ratio of the oscillating ink: contrary to an underdamped system, an overdamped system supports a jetting frequency higher than the natural frequency. [ABSTRACT FROM AUTHOR]

Published
2018
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