• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.180-180
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• 2015

Solution processed Resistive random access memory (ReRAM)은 간단한 공정 과정, 고집적도, 저렴한 가격, 대면적화 플라즈마 데미지 최소화 등의 장점으로 차세대 비휘발성 메모리로 써 많은 관심을 받고 있으며, 주로 high-k 물질인 HfOx, TiOx, ZnO 가 이용 된다. IGZO와 ZTO와 같은 산화물 반도체는 높은 이동도, 대면적화, 넓은 밴드갭으로 인하여 투명한 장점으로 LCDs (Liquid crystal displays)에 이용 가능하며, 최근에는 IGZO와 ZTO에서 Resistive Switching (RS) 특성을 확인한 논문이 보고되면서 IGZO와 ZTO를 ReRAM의 switching medium와 TFT의 active material로써 동시에 활용하는 것에 많은 관심을 받고 있다. 이와 같은 산화물 반도체는 flat panel display 회로에 TFT와 ReRAM의 active layer로써 집적가능 하며 systems-on-panels (SOP)에 적용 가능하다. 하지만 IGZO 보다는 ZTO가 In과 Ga을 포함하지 않기 때문에 저렴하다. 그러므로 IGZO를 대신하는 물질로 ZTO가 각광 받고 있다. 본 실험에서는 ZTO film에 Al을 doping하여 메모리 특성을 평가하였다. 실험 방법으로는 p-type Si에 습식산화를 통하여 SiO2를 300 nm 성장시킨 기판을 사용하였다. 그리고 Electron beam evaporator를 이용하여 Ti를 10 nm, Pt를 100 nm 증착 한다. 용액은 Zn와 Tin의 비율을 1:1로 고정한 후 Al의 비율을 0, 0.1, 0.2의 비율로 용액을 각각 제작하였다. 이 용액을 이용하여 Pt 위에 spin coating방법을 이용하여 1000 rpm 10초, 6000 rpm 30초의 조건으로 AZTO (Al-ZnO-Tin-Oxide) 박막을 증착한 뒤, solvent 및 불순물 제거를 위하여 $250^{\circ}C$의 온도로 30분 동안 열처리를 진행하였다. 이후 Electron beam evaporator를 이용하여 top electrode인 Ti를 100 nm 증착하였다. 제작된 메모리의 전기적 특성은 HP 4156B semiconductor parameter analyzer를 이용하여 측정하였다. 측정 결과, AZTO (0:1:1, 0.1:1:1, 0.2:1:1)를 이용하여 제작한 ReRAM에서 RS특성을 얻었으며 104 s이상의 신뢰성 있는 data retention특성을 확인하였다. 그리고 Al의 비율이 증가할수록 on/off ratio가 증가하고 endurance 특성이 향상되는 것을 확인하였다. 결론적으로 Al을 doping함으로써 ZTO film의 메모리 특성을 향상 시켰으며 AZTO film을 메모리와 트랜지스터의 active layer로써 활용 가능할 것으로 기대된다.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.116.1-116.1
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• 2011

Materials with a combination of high electrical conductivity and optical transparency are important components of many electronic and optoelectronic devices such as liquid crystal displays, solar cells, and light emitting diodes. In this study, to fabricate a low-resistance and high optical transparent electrode film for organic photovoltaic, the following steps were performed: the design and manufacture of an electroforming stamp mold, the fabrication of thermal roll imprinted (TRI) poly-carbonate (PC) patterned films, the manufacture of high-conductivity and low-resistance Ag paste which was filled into patterned PC film using a doctor blade process and then coated with a thin film layer of conductive polymer by a spin coating process. As a result of these imprinting processes the PC films obtained a line width of $10{\pm}0.5{\mu}m$, a channel length of $500{\pm}2{\mu}m$, and a pattern depth of $7.34{\pm}0.5{\mu}m$. After the Ag paste was used to fill part of the patterned film with conductive polymer coating, the following parameters were obtained: a sheet resistance of $9.65{\Omega}$/sq, optical transparency values were 83.69 % at a wavelength of 550 nm.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.312-312
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• 2013

GaN based light emitting diodes (LEDs) are important devices that are being used extensively in our daily life. For example, these devices are used in traffic light lamps, outdoor full-color displays and backlight of liquid crystal display panels. To realize high-brightness GaN based LEDs for solid-state lighting applications, the development of p-type ohmic electrodes that have low contact resistivity, high optical transmittance and high refractive index is essential. To this effect, indiumtin oxide (ITO) have been investigated for LEDs. Among the transparent electrodes for LEDs, ITO has been one of the promising electrodes on p-GaN layers owing to its excellent properties in optical, electrical conductivity, substrate adhesion, hardness, and chemical inertness. Sputtering and e-beam evaporation techniques are the most commonly used deposition methods. Commonly, ITO films on p-GaN by sputtering have better transmittance and resistivity than ITO films on p-GaN by e-bam evaporation. However, ITO films on p-GaN by sputtering have higher specific contact resistance, it has been demonstrated that this is due to possible plasma damage on the p-GaN in the sputtering process. In this paper, we have investigated the advanced sputtering using plasma damage-free p-electrode. Prepared the ITO films on the GaN based LEDs by e-beam evaporation, normal sputtering and advanced sputtering. The ITO films on GaN based LEDs by sputtering showed better transmittance and sheets resistance than ITO films on the GaN based LEDs by e-beam evaporation. Finally, fabricated of GaN based LEDs by using advanced sputtering. And compared the electrical properties (measurement by using C-TLM) and structural properties (HR-TEM and FE-SEM) of ITO films on GaN based LEDs produced by e-beam evaporation, normal sputtering and advanced sputtering. As a result, It is expected to form plasma damage free-electrode, and better light output power and break down voltage than LEDs by e-beam evaporation and normal sputter.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.5998-6016
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• 2017

In thin-film transistor liquid-crystal displays (TFT-LCDs), which are most commonly used in mobile devices, the backlight accounts for about 70% of the power consumption. Therefore, most low-power-related studies focus on realizing power savings through backlight dimming. Image compensation is performed to mitigate the visual distortion caused by the backlight dimming. Therefore, popular techniques include pixel compensation for brightness recovery and contrast enhancement, such as histogram equalization. However, existing pixel compensation techniques often have limitations with respect to blur owing to the pixel saturation phenomenon, or because contrast enhancement cannot adequately satisfy the human visual system (HVS). To overcome these, in this study, we propose a novel dimming technique to achieve both power saving and HVS-awareness by combining the pixel compensation and histogram specifications, which convert the original cumulative density function (CDF) by designing and using the desired CDF of an image. Because the process of obtaining the desired CDF is customized to consider image characteristics, histogram specification is found to achieve better HVS-awareness than histogram equalization. For the experiments, we employ the LIVE image database, and we use the structural similarity (SSIM) index to measure the degree of visual satisfaction. The experimental results show that the proposed technique achieves up to 15.9% increase in the SSIM index compared with existing dimming techniques that use pixel compensation and histogram equalization in the case of the same low-power ratio. Further, the results indicate that it achieves improved HVS-awareness and increased power saving concurrently compared with previous techniques.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.174-178
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• 2006

Pyramid shape of micro pattern is applied to the light guide panel (LGP) to enhance the uniformity of the brightness of the LCD. The micro pyramids are molded in intaglio on the surface of the LGP. The size of each pyramid is 5$\mu$m $\times$ 5$\mu$m on bottom and the height is about 3.5$\mu$m. The pyramids are distributed on the LGP surface randomly to be sparser where the light comes in and denser at the opposite side as a result of a simulation using lightools$^{TM}$ Based on this design, a silicon pattern master and a nickel stamper are fabricated by MEMS process and electro plating process. Intaglio micro pyramids are fabricated on the 6' of silicon wafer from the anisotropic etching using KOH and the process time, temperature of the KOH solution, etc are optimized to obtain precise shape of the pattern. A Wi stamper is fabricated from this pattern master by electro plating process and the embossed pyramid patterns turns out to be well defined on the stamper. Adopting this stamper to the mold base with two cavities, 1.8' and 3.6' LGPs are injection molded.

• 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 Vacuum Society Conference
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• 2010.08a
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• pp.168-168
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• 2010

Transparent conduction oxides (TCOs) films is extensively reported for optoelectronic devices application such as touch panels, solar cells, liquid crystal displays (LCDs), and organic light emitting diodes(OLEDs). Among the many TCO film, indium tin oxide(ITO) is in great demand due to the growth of flat panel display industry. However, indium is not only high cost but also its deposits dwindling. Therefore, many studies are being done on the transparent conductive oxides(TCOs). We fabricated a target of IZTO(In2O3:ZnO:SnO2=70:15:15 wt.%) reduced indium. Then, IZTO thin films were deposited on glass substrates by pulsed DC magnetron sputtering with various oxygen flow ratio. The substrate temperature was fixed at the room temperature. We investigated the electrical, optical, structural properties of IZTO thin films. The electrical properties of IZTO thin films were dependent on the oxygen partial pressure. As a result, the most excellent properties of IZTO thin films were obtained at the 3% of oxygen flow rate with the low resistivity of $7.236{\times}10^{-4}{\Omega}cm$. And also the optical properties of IZTO thin films were shown the good transmittance over 80%. These IZTO thin films were used to fabricated organic light emitting diodes(OLEDs) as anode and the device performances studied. The OLED with an IZTO anode deposited at optimized deposition condition showed good brightness properties. Therefore, IZTO has utility value of TCO electrode although it reduced indium and we expect it is possible for the IZTO to apply to flexible display due to the low processing temperature.

• Journal of the Korean Graphic Arts Communication Society
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• v.29 no.3
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• pp.105-124
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• 2011

TFT-LCD consists of LCD panel on the top, circuit unit on the side and BLU on the bottom. The recent development issues of BLU-dependent TFT-LCD have been power consumption minimization, slimmerization and size maximization. As a result of this trend, LED is adopted as BLU instead of CCFL to increase brightness and to reduce thickness. In liquid crystal displays, the light efficiency is below 10% due to the loss of light in the path from a light source to an LCD panel and presence of absorptive polarizer. This low efficiency results in low brightness and high power consumption. One way to circumvent this situation is to use a reflective polarizer between backlight units and LCD panels. Since a nano-wire grid polarizer has been known as a reflective polarizer, an idea was proposed that it can be used for the enhancement of the brightness of LCD. The use of reflective polarizing film is increasing as edge type LED TV and 3D TV markets are growing. This study has been carried out to fabrication of the nano-wire grid polarizer(NWGP) and investigated the brightness enhancement of LCD through polarization recycling by placing a NWGP between an c and a backlight unit. NWGPs with a pitch of 200nm were fabricated using laser interference lithography and aluminum sputtering and wet etching. And The NWGP fabrication process was using by the UV imprinting and was applied to plastic PET film. In this case, the brightness of an LCD with NWGPs was 1.21 times higher than that without NWGPs due to polarization recycling.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.60.2-60.2
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• 2012

기술의 발전이 비약적으로 성장하면서, 소비자의 요구는 빠르게 변하고 있다. 전자 소자를 응용한 제품 시장은 매해를 거듭할 수록 빠른 속도로 성능을 향상시키고 있다. 이에 따라 디스플레이 시장에서 가장 큰 관심은 작은 화면에서도 높은 해상도를 요구하고, 수광형의 구동방식이 아닌 능동형 구동방식을 갖는 AMOLED (Active Matrix Organic Light Emitted Diode)를 선호하고 있으며, 빠른 응답속도 기반을 갖는 표시소자를 요구하고 있다. 제품 생산자들의 고민은 기존의 비정질 실리콘 기반의 LCD (Liquid crystal display) 구동소자와 공정을 이용하여 소비자의 욕구에 접근하기가 점점 어려워지고 있다. 최근 이러한 문제점을 해결하고자 하는 노력들중에서 산화물 반도체 재료와 이를 이용한 박막 트랜지스터 개발이 큰 관심을 갖고 있다. 최근 InGaZnO 산화물 반도체 재료는 기존의 비정질 실리콘 반도체 재료 보다 높은 전계 이동도(> $10cm^2/V.s$)를 보이고 있으며, 비정질 실리콘 박막 트랜지스터의 구조에서 산화물 반도체 재료의 대체만으로 효과가 보일 수 있어서 큰 연구가 진행되어져 왔다. 하지만, InGaZnO 산화물 박막 트랜지스터에 대한 소자를 AMOLED에 적용할 때, 기존의 LTPS (low temperature poly-slicon)에서는 발견되지 않았던 소자의 전계신뢰성과 이동도 한계가 문제로 제기되었다. 또한, Indium이라는 희소원소의 사용은 향후 공정 단가와 희소 물질에 대한 위협등에 의하여 새로운 산화물 반도체 재료에 대한 요구와 관심이 발생하고 있다. 본 발표에서는 기존의 산화물 반도체 재료에 대한 차세대 디스플레이인 AMOLED와 유연 디스플레이에 대한 응용 가능성을 발표할 예정이다. 또한 산화물 반도체 재료의 신뢰성 문제에 대한 해결방법으로 신규 산화물 반도체 재료에 대한 연구 방향과 indium-free 계열을 이용한 저원가 산화물 반도체 연구에 대하여 소개할 예정이다. 앞으로 산화물 반도체 재료에 대한 연구와 응용은 기존의 실리콘 반도체 틀을 벗어난 새로운 응용분야를 열어줄 수 있을 것으로 기대하고 있으며, 그 기대에 대한 몇가지 예를 통하여 재료와 소자의 응용 가능성을 논의할 예정이다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.4
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• pp.161-168
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• 2001

Organic thin film transitors(TFTs) are of interest for use in broad area electronic applications. For example, in active matrix liquid crystal displays(AMLCDs), organic TFTs would allow the use of inexpensive, light-weight, flexible, and mechanically rugged plastic substrates as an alternative to the glass substrates needed for commonly used hydrogenated amorphous silicon(a-Si:H). Recently pentacene TFTs with carrier field effect, mobility as large as 2 $cm^2V^{-1}s^{-1}$ have been reported for TFTs fabricated on silicon substrates, and it is higher than that of a-Si:H. But these TFTs are fabricated on silicon wafer and $SiO_2$ was used as a gate insulator. $SiO_2$ deposition process requires a high insulator which is polyimide and photo acryl. We investigated trasfer and output characteristics of the thin film transistors having active layer of pentacene. We calculated field effect mobility and on/off ratio from transfer characteristics of pentacene thin film transistor, and measured IR absorption spectrum of polymide used as the gate dielectric layer. It was found that using the photo acryl as a gate insulator, threshold voltage decreased from -12.5 V to -7 V, field effect mobility increased from 0.012 $cm^2V^{-1}s^{-1}$ to 0.039 $cm^2V^{-1}s^{-1}$ , and on/off current ratio increased from $10^5\;to\;10^6$. It seems that TFTs using photo acryl gate insulator is apt to form channel than TFTs using polyimide gate insulator.