• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.5
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• pp.12-18
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• 2008

Ag paste was employed for source and drain electrode of OTFTs and for the data metal lines of OTFT-OLED array on PC(polycarbonate) substrate. We tested two kinds of Ag-pastes such as pastes for 325 mesh and 500 mesh screen mask to examine the pattern ability and electrical performance for OTFTs. The minimum feature size was 60 ${\mu}m$ for 325 mesh screen mask and 40 ${\mu}m$ for 500 mesh screen mask. The conductivity was 60 $m{\Omega}/\square$ for 325 mesh and 133.1 $m{\Omega}/\square$ for 500 mesh. For the OTFT performance the mobility was 0.35 $cm^2/V{\cdot}sec$ and 0.12 $cm^2/V{\cdot}sec$, threshold voltage was -4.7 V and 0.9 V, respectively, and on/off current ratio was ${\sim}10^5$, for both screen masks. We applied the 500 mash Ag paste to OTFT-OLED array because of its good patterning property. The pixel was composed of two OTFTs and one capacitor and one OLED in the area of $2mm{\times}2mm$. The panel successfully worked in active mode operation even though there were a few bad pixels.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.117-122
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• 2016

White organic light-emitting diodes with a structure of indium-tin-oxide [ITO]/N,N-diphenyl-N,N-bis-[4-(phenylm-tolvlamino)-phenyl]-biphenyl-4,4-diamine [DNTPD]/[2,3-f:2, 2-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile [HATCN]/1,1-bis(di-4-poly-aminophenyl) cyclo -hexane [TAPC]/emission layers doped with three color dopants/4,7-diphenyl-1,10-phenanthroline [Bphen]/$Cs_2CO_3$/Al were fabricated and evaluated. In the emission layer [EML], N,N-dicarbazolyl-3,5-benzene [mCP] was used as a single host and bis(2-phenyl quinolinato)-acetylacetonate iridium(III) [Ir(pq)2acac]/fac-tris(2-phenylpyridinato) iridium(III) $[Ir(ppy)_3]$/iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate [FIrpic] were used as red/green/blue dopants, respectively. The fabricated devices were divided into five types (D1, D2, D3, D4, D5) according to the structure of the emission layer. The electroluminescence spectra showed three peak emissions at the wavelengths of blue (472~473 nm), green (495~500 nm), and red (589~595 nm). Among the fabricated devices, the device of D1 doped in a mixed fashion with a single emission layer showed the highest values of luminance and quantum efficiency at the given voltage. However, the emission color of D1 was not pure white but orange, with Commission Internationale de L'Eclairage [CIE] coordinates of (x = 0.41~0.45, y = 0.41) depending on the applied voltages. On the other hand, device D5, with a double emission layer of $mCP:[Ir(pq)_2acac(3%)+Ir(ppy)_3(0.5%)]$/mCP:[FIrpic(10%)], showed a nearly pure white color with CIE coordinates of (x = 0.34~0.35, y = 0.35~0.37) under applied voltage in the range of 6~10 V. The luminance and quantum efficiency of D5 were $17,160cd/m^2$ and 3.8% at 10 V, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.457-457
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• 2010

Flexible organic light emitting diodes (F-OLEDs) requires excellent moisture permeation barriers to minimize the degradation of the F-OLEDs device. Specifically, F-OLEDs device 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 life time of F-OLEDs, 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. Thus, $Al_2O_3/TiO_2$ multi-layer was deposited onto the polyethersulfon (PES) substrate by electron cyclotron resonance atomic layer deposition (ECR-ALD), and the water vapor transmission rates (WVTR) were measured. WVTR of moisture permeation barriers is dependent upon density of films and initial state of polymer surface. A significant reduction of WVTR was achieved by increasing density of films and by applying low plasma induced interlayer on the PES substrate. In order to minimize damage of polymer surface, a 10 nm thick $TiO_2$ was deposited on PES prior to a $Al_2O_3$ ECR-ALD process. High quality barriers were developed from $Al_2O_3$ barriers on the $TiO_2$ interlayer. WVTR of $Al_2O_3$ by introducing $TiO_2$ interlayer was recorded in the range of $10^{-3}g/m^2.day$ at $38^{\circ}C$ and 100% relative humidity using a MOCON instrument. The WVTR was two orders of magnitude smaller than $Al_2O_3$ barriers directly grown on PES substrate without the $TiO_2$ interlayer. Thus, we can consider that the $Al_2O_3/TiO_2$ multi-layer passivation can be one of the most suitable F-OLEDs passivation films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.299-299
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• 2007

후막형 무기 EL (electro-luminescence) 소자는 제조공정이 간단하고, 얇고, 가볍고, 유연한 동의 많은 장점들 때문에 휴대폰의 키패드 (key-pad) 및 광고용 back-light용으로 사용되고 있다. 이 무기 EL 소자는 비교적 손쉬운 스크린 프린팅 (screen-printing) 법으로 대면적을 제작할 수 있지만, LED (light emitting diode) 등과 비교하여 밝기가 낮아서 그 응용 분야가 제한되고 있다. EL 소자의 형광층은 전면 전극과 후면 전극 사이에 위치한다. EL은 이 형광층에 고 전기장이 걸릴 때, 전기장에 의해 가속된 전자가 형광층 내부에 첨가된 발광 중심의 전자를 여기시키고, 여기된 전자가 다시 바닥상태로 완화될 때 빛이 방출되는 현상이다. 즉, EL 소자는 이러한 전자 발광 현상을 이용한 소자로서, 전압 인가 시 발광 면 전체가 균일하게 발팡하는 평면 광원이다. 이러한 EL 소자에서 휘도의 증가는 후면 전극과 형광층 사이에 삽입되는 유전체 층의 특성과 밀접한 연관성이 있다. 본 연구에서는 고휘도 무기 EL 소자를 제작하기 위하여 이 유전체 층의 특성과 소자의 성능 사이의 관계를 알아보고자 하였다. 유전체 층에 사용하기 위해서 $BaTiO_3$-PVDF (polyvinylidene fluoride)의 복합체 필름을 제조하였다. 먼저 이 복합체 필름을 스크린 프린팅 (screen printing) 법으로 코팅하기 위한 페이스트 제작을 위해서, PVDF 수지를 용제에 녹였다. 그 다음, 일반 혼합기 및 삼단 롤밀 혼합기 (3-roll milling mixer) 등을 이용하여 $BaTiO_3$ 분말과 PVDF 용액을 다양한 비율로 혼합하여 페이스트를 제조하였다. ITO가 증착된 PET Film에 스크린 프린팅 법을 사용하여 형광층, 유전층, 배면 전극 등을 차례로 코팅하였다. $BaTiO_3$ (BT) 분말과 복합체 필름의 XRD 분석 결과, 분말 시료와 복합체 시료 모두 페로브스카이트 구조의 BT 회절선만 관찰되었다. 복합체의 단면 SEM 관찰에서는, BT 분말의 무게비가 증가할수록 더 치밀한 구조를 보여줌을 확인하였다. 또 EL소자의 유전상수와 휘도도 BT 분말의 혼합비가 증가할수록 증가하였다. 본 연구에서 제작한 무기 EL 소자의 최대 휘도는 약 $130\;cd/m^2$ 정도로 측정되었는데, 이는 휴대폰 키패드의 back-light용 광원으로 사용하기 충분하다고 판단되어진다.

• Journal of the korean academy of Pediatric Dentistry
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• v.47 no.1
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• pp.70-77
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• 2020

The present study is aimed to assess the effect of antimicrobial photodynamic therapy (aPDT) on Streptococcus mutans biofilm through teeth whitening light emitting diode (LED). Planktonic and dynamic biofilm state cultures of S. mutans were used. Erythrosine 20 μM/L was used as the photosensitizer. Irradiation was performed by exposing cultures to clinic and homecare whitening LEDs for 15 minutes. The viability was measured through Colony Forming Unit counts and confocal laser scanning microscopy. aPDT using whitening LEDs and erythrosine significantly decreased the CFU count of S. mutans compared to that in the control group. Dynamic biofilm group showed more resistant features to aPDT compared with planktonic state. Clinic and homecare whitening LED device showed similar antimicrobial effect. The whitening LED, which could irradiate the entire oral arch, showed a significant photodynamic effect on cariogenic S. mutans biofilm. aPDT mediated by erythrosine and LEDs used for teeth whitening exhibited promising antimicrobial activity.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.17-30
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• 2020

An optical televiewer is a geophysical logging device that produces continuous high-resolution full-azimuth images of a borehole wall using a light-emitting-diode and a complementary metal-oxide semiconductor image sensor to provide valuable information on subsurface discontinuities. Recently, borehole imaging logging has been applied in many fields, including ground subsidence monitoring, rock mass integrity evaluation, stress-induced fracture detection, and glacial annual-layer measurements in polar regions. Widely used commercial borehole imaging logging systems typically have limitations depending on equipment specifications, meaning that it is necessary to clearly verify the scope of applications while maintaining appropriate quality control for various borehole conditions. However, it is difficult to directly check the accuracy, implementation, and reliability for outcomes, as images derived from an optical televiewer constitute in situ data. In this study, we designed and constructed a modular fractured borehole model having similar conditions to a borehole environment to report unprecedented results regarding reliable data acquisition and processing. We investigate sonde magnetometer accuracy, color realization, and fracture resolution, and suggest data processing methods to obtain accurate aperture measurements. The experiment involving the fractured borehole model should enhance not only measurement quality but also interpretations of high-resolution and reliable optical imaging logs.

• Journal of the Korean Electrochemical Society
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• v.2 no.1
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• pp.17-22
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• 1999

Since the use of porous silicon for microsensors and microactuators is in the euly stage of study, only several application devices, such as light-emitting diodes and chemical sensors have so far been demonstrated. In this paper we present an overview of the present status of porous silicon sensors and actuators research with special emphasis on the applications of chemical sensors and optical devices. The capacitive type porous silicon humidity sensors had a nonlinear capacitance-humidity characteristic and a good sensitivity at higher humidity above $40\%RH$. The porous silicon $n^+-p-n^+$ device showed a sharp increase in current when exposed to an ethanol vapor. The $p^+-PSi-n^+$ diode fabricated on porous silicon diaphragm exhibited an optical switching characteristic, opening up its utility as an optical sensor or switch. The photoluminescence (PL) spectrum, taken from porous silicon under 365 nm excitation, had a broad emission, peaked at -610 nm. The electroluminescence(EL) from ITO/PSi/In LED had a broader spectrum with a blue shifted peak at around 535nm than that of the PL.

• Korean Journal of Optics and Photonics
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• v.25 no.1
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• pp.38-43
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• 2014

An external cavity laser supporting two wavelengths is demonstrated by incorporating polymer waveguide Bragg reflectors and a superluminescent light-emitting diode. An oversized rib waveguide structure and Bragg gratings are designed by using the effective-index and transmission-matrix methods. Bragg gratings with different periods are inscribed on a polymer waveguide through double-exposure laser interferometry. In order to tune the cavity loss affected by the reflectivity of Bragg gratings, a Bragg reflectors with varying length is incorporated. Two-wavelength-mode lasing is achieved for the device consisting of 2-mm long, 537-nm period gratings and 2.2-mm long, 540-nm period gratings; the lasing wavelengths are 1554 nm and 1564 nm, with an output power close to 0 dBm, a 20-dB bandwidth of 0.2 nm, and a side-mode suppression ratio of 45 dB.

• Journal of Korea Society of Industrial Information Systems
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• v.12 no.3
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• pp.116-123
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• 2007

Despite the number of backlight manufacturer is increased as the market of flat panel display equipments and related development devices is enlarged, the inspection based on the human eye is still used in many backlight production lines. The defects such as particle, spot and scratch on the light emitting surface of the backlight prevent the LCD device from displaying the colors correctly. From that manual inspection it is difficult to maintain the quality of backlight consistently because the accuracy and the speed of the inspection may change with the physical condition of the operater. In this paper we studied on the development of automatic backlight surface defect inspection system. For this, we made up of the computer vision system and we developed the main program with various user interfaces to operate the inspection system effectively. And we developed the image processing module to extract the defect information. Furthermore, we presented the labeling process to reconstruct defect regions using the labeling table and the defect index. From the experimental results, we found that our system can detect all defect regions identified from human eye and it is sufficient to substitute for the conventional surface inspection.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.173-173
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• 2010

Recently, a patterned sapphire substrate (PSS) has been intensively used as one of the effective ways to reduce the dislocation density for the III-nitride epitaxial layers aiming for the application of high-performance, especially high-brightness, light-emitting diodes (LEDs). In this paper, we analyze the growth kinetics of the atoms and crystalline quality for the undopped-GaN depending on the facets of the pattern fabricated on a sapphire substrate. The effects of the PSS on the device characteristics of InGaN/GaN LEDs were also investigated. Several GaN samples were grown on the PSS under the different growth conditions. And the undoped-GaN layer was grown on a planar sapphire substrate as a reference. For the (002) plane of the undoped-GaN layer, as an example, the line-width broadening of the x-ray diffraction (XRD) spectrum on a planar sapphire substrate is 216.0 arcsec which is significantly narrower than that of 277.2 arcsec for the PSS. However, the line-width broadening for the (102) plane on the planar sapphire substrate (363.6 arcsec) is larger than that for the PSS (309.6 arcsec). Even though the growth parameters such as growth temperature, growth time, and pressure were systematically changed, this kind of trend in the line-width broadening of XRD spectrum was similar. The emission wavelength of the undoped-GaN layer on the PSS was red-shifted by 5.7 nm from that of the conventional LEDs (364.1 nm) under the same growth conditions. In addition, the intensity for the GaN layer on the PSS was three times larger than that of the planar case. The spatial variation in the emission wavelength of the undoped-GaN layer on the PSS was statistically ${\pm}0.5\;nm$ obtained from the photoluminescence mapping results throughout the whole wafer. These results will be discussed in terms of the mixed dislocation depending on the facets and the period of the patterns.