• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.1
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• pp.28-34
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• 2010

The pulse width modulation(PWM) method has been generally used as conventional method controlling luminance of LED(light emitting diode). PWM method as analog method with a relation that duty ratio of LED be proportional to luminance has weak point that it is not compatible with digital method of communication etc. In this paper, a experiment is conducted which the luminance of RGB LED be controlled by digital method. For this, the LED digital control system is developed which consist of LED driving circuits and digital logic circuits. By controlling the number of pluses on RGB LED versus digital input, various lighting colors is implemented and digital codes are optimized in order that measured x, y chromaticity coordinates of lighting colors are comprised in the CIE chromaticity coordinates area of targeted lighting colors. The result of this study can be utilized usefully in research on implementing full color by using remote control of LED lamp with digital communication.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.40 no.1
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• pp.114-123
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• 2017

The global small and mid-sized display market is changing from thin film transistor-liquid crystal display to organic light emitting diode (OLED). Reflecting these market conditions, the domestic and overseas display panel industry is making great effort to innovate OLED technology and incease productivity. However, current OLED production technology has not been able to satisfy the quality requirement levels by customers, as the market demand for OLED is becoming more and more diversified. In addition, as OLED panel production technology levels to satisfy customers' requirement become higher, product quality problems are persistently generated in OLED deposition process. These problems not only decrease the production yield but also cause a second problem of deteriorating productivity. Based on these observations, in this study, we suggest TRIZ-based improvement of defects caused by glass pixel position deformation, which is one of quality deterioration problems in small and medium OLED deposition process. Specifically, we derive various factors affecting the glass pixel position shift by using cause and effect diagram and identify radical reasons by using XY-matrix. As a result, it is confirmed that glass heat distortion due to the high temperature of the OLED deposition process is the most influential factor in the glass pixel position shift. In order to solve the identified factors, we analyzed the cause and mechanism of glass thermal deformation. We suggest an efficient method to minimize glass thermal deformation by applying the improvement plan of facilities using contradiction matrix in TRIZ. We show that the suggested method can decrease the glass temperature change by about 23% through an experiment.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.63-68
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• 2011

The investigation is directed to lead free (Pb-free) frits that can be used for organic light emitting diode, plasma display screen devices and other sealing materials. $P_2O_5$-SnO system glasses have been prepared for Pb-free low temperature glass frit. Structure and properties of the glasses with the composition SnO-$xB_2O_3-(60-x)P_2O_5$ (x=0, 5, 10, 15, 20, 25, 30, 35, 40 mol%) were characterized by infrared spectra (IR), X-ray diffraction(XRD), Density, Molar volume, Thermo mechanical analysis(TMA) and weight loss after immersion test. Glass transition temperature($T_g$), dilatometric softening temperature($T_d$) and chemical durability increased, and coefficient of thermal expansion($\alpha$) decrease with the substitution of $B_2O_3$ for $P_2O_5$ in the range of 0~25 mol%.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1170-1176
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• 2003

We developed an evolutionary optimization process involving a genetic algorithm and combinatorial chemistry (combi-chem), which was tailored exclusively for tile development of LED phosphors with a high luminescent efficiency, when excited by soft ultra violet irradiation. The ultimate goal of our study was to develop oxide red phosphors, which are suitable for three-band white Light Emitting Diodes (LED). To accomplish this, a computational evolutionary optimization process was adopted to screen a Eu$^{3+}$-doped alkali earth borosilicate system. The genetic algorithm is a well-known, very efficient heuristic optimization method and combi-chem is also a powerful tool for use in an actual experimental optimization process. Therefore the combination of a genetic algorithm and combi-chem would enhance the searching efficiency when applied to phosphor screening. Vertical simulations and an actual synthesis were carried out and promising red phosphors for three-band white LED applications, such as Eu$_{0.14}$Mg$_{0.18}$Ca$_{0.07}$Ba$_{0.12}$B$_{0.17}$Si$_{0.32}$O$_{\delta}$, were obtained.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.63-68
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• 2013

The purpose of this study is to investigate the cooling performance of radial heat sink used for high power LED lightings by natural convection cooling with surrounding air. Experimental and numerical analyses are carried out together. Parametric studies are performed to compare the effects of geometric parameters in radial heat sink such as the number of fins, fin height, fin length, and thickness of fin base as well as the surface coatings of radial heat sink. In this study, the cooling of 60 W LED lamp is examined with radiative heat transfer considered as well as natural convection. Numerical results show the optimum condition when the number of fin is 40, heat sink height is 120 mm, fin length is 15 mm, and fin base thickness is 3 mm. The difference in temperature of the LED metal PCB is within $1^{\circ}C$ between numerical analyses and experimental results. Also, the CNT coating on the heat sink surface is found to increase the cooling performance significantly.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.160-160
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• 2010

Organic electronic devices require a passivation layer to ensure sufficient lifetime. Specifically, flexible organic electronic devices need a barrier layer that transmits less than $10^{-6}\;g/m^2/day$ of water and $10^{-5}\;g/m^2/day$ of oxygen. To increase the lifetime of organic electronic device, therefore, it is indispensable to protect the organic materials from water and oxygen. Severe groups have reported on multi-layerd barriers consisting inorganic thin films deposited by plasma enhenced chemical deposition (PECVD) or sputtering. However, it is difficult to control the formation of granular-type morphology and microscopic pinholes in PECVD and sputtering. On the contrary, atomic layer deoposition (ALD) is free of pinhole, highly uniform, conformal films and show good step coverage. In this study, the passivation layer was deposited using single-process PEALD. The passivation layer, in our case, was a bilayer system consisting of $Al_2O_3$ films and a $TiO_2$ buffer layer on a poly (ether sulfon) (PES) substrate. Because the deposition temperature and plasma power have a significant effect on the properties of the passivation layer, the characteristics of the $Al_2O_3$ films were investigated in terms of density under different deposition temperatures and plasma powers. The effect of the $TiO_2$ buffer layer also was also addressed. In addition, the water vapor transmission rate (WVTR) and organic light-emitting diode (OLEDs) lifetime were measured after forming a bilayer composed of $Al_2O_3/TiO_2$ on a PES substrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.367-367
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• 2014

Transparent conductive oxides (TCOs) 박막은 가시광선영역에서의 높은 투과율과 낮은 저항 특성을 동시에 갖고 있어 최근 smart windows, solar cells, liquid crystal displays (LCD), organic light emitting devices (OLED)등과 같은 최첨단 기기에 필수적인 구성요소로 활발히 사용되고 있다. 따라서, 현재까지 FTO ($SnO_2:F$), ITO ($In_2O_3:Sn$), ATO ($SnO_2:Sb$)등과 같은 다양한 TCO들이 많은 연구자들에 의해 연구되고 있다. 그 중 ITO는 우수한 전기적(${\sim}10^{-4}{\Omega}cm$) 및 광학적(~85%) 특성 때문에 현재 상업적으로 활발히 응용되고 있는 대표적인 물질이다. 하지만 ITO의 주된 구성요소인 indium은 제한적인 매장량과 과도한 소비량 때문에 원가가 비싸다는 문제점이 있다. 반면에, ATO는 우수한 전기적(${\sim}10^{-3}{\Omega}cm$) 및 광학적(~80%) 특성뿐만 아니라 구성물질들의 매장량이 풍부하여 ATO의 원가가 저렴하다는 장점을 가지고 있어 현재 ITO을 대체 할 수 물질로 관심 받고 있다 [1]. 지금까지 우수한 특성을 갖는 ATO박막을 합성하는 방법으로 sol-gel spin coating, sputtering, spray pyrolysis, chemical vapor deposition (CVD)등이 알려져 있다. 이 중에서도, sol-gel spin coating과 spray pyrolysis은 solution기반의 합성법으로 분류되며 합성과정이 간단하고 비용이 저렴하다는 장점이 있고 현재까지 많은 연구가 보고되었다. 그러나, 진공기반이 아닌 우수한 특성을 갖는 solution기반의 ATO박막을 합성하기 위해서는 새로운 합성법의 개발이 학문적으로나 산업적으로도 매우 중요한 이슈이다. 따라서, 본 연구에서는 electrospray을 활용하여 solution기반의 ATO박막을 처음으로 합성하였다. 게다가 ATO박막에 열처리온도에 따른 구조, 화학, 전기, 광학적 특성을 확인하기 위하여 X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), Hall Effect Measurement System, UV spectrophotometer를 사용하였다. 이러한 실험 결과들을 바탕으로 electrospray을 통해 합성된 solution기반의 ATO박막에 자세한 특성을 본 학회에서 다루도록 하겠다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.726-728
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• 2013

Optoelectronic arc discharge sensor was used to detect arc discharge inside power distribution panel. Arc discharge is fatal to power system once it begins, thus preventive detection is necessary before power failure occurs. Optoelectronic detection method was used to avoid direct electrical contact to power apparatus inside power distribution panel. 180 degree detection angle and detection range far exceeding 6m, which was sufficient for monitoring purpose, was achieved using the photodiode having $7.5mm^2$ of active surface area and flash source with $0.4cal/cm^2$ energy density, which is equivalent to 1.9J with $2.16cm^2$ emitting area. The response speed of arc discharge sensor was measured to be below 1 msec. The above optoelectronic arc discharge sensor was measured to be sensitive enough to detect 0.94 pC charge.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.525-532
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• 2017

The development of an inkjet-based manufacturing machine for the production of next-generation displays using organic and quantum-dot light emitting diodes at a low cost has been conducted. To employ inkjet printing in production lines of displays, the development of a high-speed inkjet-monitoring device to verify the reliable droplet jetting status from multiple nozzles is required. In this study, an inkjet monitoring device using a rotatable mirror with rotary and linear ultrasonic motors is developed in place of a conventional, linear reciprocating, motion-based inkjet monitoring device. Its performance is also demonstrated. The measurements of circular patterns with diameters of $10{\mu}m$, $30{\mu}m$, and $50{\mu}m$ are performed with the accuracies of $0.5{\pm}1.0{\mu}m$, $-1.2{\pm}0.3{\mu}m$, and $0.2{\pm}0.5{\mu}m$, respectively, within 17 sec. By optimizing the control program, the takt time can be reduced to as short as 8.6 sec.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.207-207
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• 2011

Amorphous transparent oxide semiconductors (a-TOS) have been widely studied for many optoelectronic devices such as AM-OLED (active-matrix organic light emitting diodes). Recently, Nomura et al. demonstrated high performance amorphous IGZO (In-Ga-Zn-O) TFTs.1 Despite the amorphous structure, due to the conduction band minimum (CBM) that made of spherically extended s-orbitals of the constituent metals, an a-IGZO TFT shows high mobility.2,3 But IGZO films contain high cost rare metals. Therefore, we need to investigate the alternatives. Because Aluminum has a high bond enthalpy with oxygen atom and Alumina has a high lattice energy, we try to replace Gallium with Aluminum that is high reserve low cost material. In this study, we focused on the electrical properties of IZO:Al thin films as a channel layer of TFTs. IZO:Al were deposited on unheated non-alkali glass substrates (5 cm ${\times}$ 5 cm) by magnetron co-sputtering system with two cathodes equipped with IZO target and Al target, respectively. The sintered ceramic IZO disc (3 inch ${\phi}$, 5 mm t) and metal Al target (3 inch ${\phi}$, 5 mm t) are used for deposition. The O2 gas was used as the reactive gas to control carrier concentration and mobility. Deposition was carried out under various sputtering conditions to investigate the effect of sputtering process on the characteristics of IZO:Al thin films. Correlation between sputtering factors and electronic properties of the film will be discussed in detail.