• 한국초전도학회:학술대회논문집
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• v.9
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• pp.102-106
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• 1999

We have designed and fabricated a four-bit shift register circuit using YBCO bicrystal junctions and experimentally tested its operations by a computer-controlled digital measurement set-up. Laser ablated YBCO thin films with clean surface were used in this work. The circuit consists of the shift register and two read SQUIDs placed next to each sides of the shift register. The SQUIDs were inductively coupled to the nearby shift register stages. A probe equipped with high speed coax lines were used in this experiment. The major obstacle in testing the circuit was the interference between the read SQUIDs and we solved the problem by finding the correct operation points of the SQUIDs from the simultaneously measured modulation curves. Loaded Data("1" or "0") were successfully shifted from a stage to the next one by a controlled current pulse injected to the bias lines located between the stages and the data shifts were correctly monitored by the read SQUIDs

• Korean Journal of Materials Research
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• v.23 no.8
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• pp.435-440
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• 2013

Transparent and conducting thin films of Ta-doped $SnO_2$ were fabricated on a glass substrate by a pulse laser deposition(PLD) method. The structural, optical, and electrical properties of these films were investigated as a function of doping level, oxygen partial pressure, substrate temperature, and film thickness. XRD results revealed that all the deposited films were polycrystalline and the intensity of the (211) plane of $SnO_2$ decreased with an increase of Ta content. However, the orientation of the films changed from (211) to (110) with an increase in oxygen partial pressure (40 to 100 mTorr) and substrate temperature. The crystallinity of the films also increased with the substrate temperature. The electrical resistivity measurements showed that the resistivity of the films decreased with an increase in Ta doping, which exhibited the lowest resistivity (${\rho}{\sim}1.1{\times}10^{-3}{\Omega}{\cdot}cm$) for 10 wt% Ta-doped $SnO_2$ film, and then increased further. However, the resistivity continuously decreased with the oxygen partial pressure and substrate temperature. The optical bandgap of the 10 wt% Ta-doped $SnO_2$ film increased (3.67 to 3.78 eV) with an increase in film thickness from 100-700 nm, and the figure of merit revealed an increasing trend with the film thickness.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.345-350
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• 2007

The characteristics of the supercontinuum generated in photonic crystal fibers were investigated by using the generalized nonlinear $Schr\"{o}dinger$ equation and the split-step Fourier method. Based on the simulated results, we generated the supercontinuum spectrum with the flatness of ${\pm}4dB$ in the wavelength range of 650 to 900 nm by employing a 200-fs pulse of Ti:sapphire laser and a commercial photonic crystal fiber.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1100-1109
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• 2006

In this study, two different technologies which can measure temperature simultaneously at many points are introduced. One is to use a thermal sensor cable that is comprised of addressable thermal sensors connected in parallel within a single cable. The other is to use an optic fiber with Distributed Temperature Sensing (DTS) system. The difference between two technologies can be summarized as follows. A thermal sensor cable has a concept of 'point sensing' that can measure temperature at accurate position of a thermal sensor. So the accuracy and resolution of temperature measurement are up to the ability of the thermal sensor. Whereas optic fiber sensor has a concept of 'distributed sensing' because temperature is measured by ratio of Stokes and anti-Stokes component intensities of Raman backscatter that is generated when laser pulse travels along an optic fiber. It's resolution is determined by measuring distance, measuring time and spatial resolution. The purpose of this study is that application targets of two temperature measurement techniques are checked in technical and economical phases by examining the strength and weakness of them. Considering the functions and characteristics of two techniques, the thermal sensor cable will be suitable to apply to the assessment of groundwater flow, geothermal distribution and grouting efficiency within 300m distance. It is expected that the optic fiber sensor can be widely utilized at various fields (for example: pipe line inspection, tunnel fire detection, power line monitoring etc.) which need an information of temperature distribution over relatively long distance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.669-676
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• 2013

In this study, we introduce a polymer(polyimide) based pressure sensor to measure real-time heart beat and blood pressure. The sensor have been designed with consideration of skin compatibility of material, cost effectiveness, manufacturability and wireless detection. The designed sensor was composed of inductor coils and an air-gap capacitor which generate self-resonant frequency when electrical source is applied on the system. The sensor was obtained with metalization, etching, photolithography, polymer adhesive bonding and laser cutting. The fabricated sensor was shaped in circular type with 10mm diameter and 0.45 mm thickness to fit radial artery. Resonant frequencies of the fabricated sensors were in the range of 91~96 MHz on 760 mmHg pressurized environment. Also the sensor has good linearity without any pressure-frequency hysteresis. Sensitivity of the sensor was 145.5 kHz/mmHg and accuracy was less than 2 mmHg. Real-time heart beat measurement was executed with a developed hand-held measurement system. Possibility of real-time blood pressure measurement was showed with simulated artery system. After installation of the sensor on skin above radial artery, simple real blood pressure measurement was performed with 64 mmHg blood pressure variation.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.396-399
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• 2002

Intense quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 55 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to the molybdenum target by the electric field in the tube, the weakly ionized plasma, which consists of metal ions and electrons, forms by the target evaporating. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source grew, and the characteristic x-ray intensities of K-series lines increased. The quite sharp lines such as hard x-ray lasers were clearly observed. The quasi-monochromatic radiography was performed by a new film-less computed radiography system.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.119-124
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• 2008

In recent years, gradually increasing interest has been directed to the use of terahertz technology in nondestructive testing and non-invasive measurements, and terahertz time domain spectroscopy (THz-TDS) has become a key technology in such applications. This paper deals with the terahertz pulse generation from cadmium telluride via optical rectification process of femto-second infrared laser pulses. The measured terahertz spectrum is compared with the result of model calculation based on space-time domain nonlinear Maxwell equations for coherent frequency mixing process. The propagation process of terahertz and infra-red pulses in the material as well as the surface interference and free space diffraction effects are also considered. The experimental results are in good agreements with the calculated spectrum.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.10-10
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• 2010

가시광역에서 80% 이상의 높은 투과율과 전기전도성을 동시에 갖는 투명전도성 산화물(TCO) 박막은 LCD, PDP, OLED, 태양전지 등의 다양한 분야에 투명전극재료로서 사용되고 있다. 이들 TCO 박막은 Magnetron sputtering, Chemical vapor deposition, Pulse laser deposition, Ink jet등과 같은 다양한 방법으로 증착할 수 있지만, 대면적의 기판에 균일한 박막형성 및 박막과 기판의 높은 부착력등 양산성의 관점에서 우월성을 가지고 있기 때문에 생산라인에서는 DC magnetron sputtering법이 주로 사용되고 있다. 이 경우, 산화물 박막의 미세구조, 내부응력, 광학적 및 전기적 특성은 스퍼터링 과정에서 발생하는 고에너지 입자들의 기판입사 충격에 크게 의존하기 때문에 고품질의 TCO박막을 제작하기 위해서는 증착공정인자들의 제어는 매우 중요한 것으로 알려져 있다. 대표적 TCO박막재료로서 $In_2O_3$계, ZnO계 및 $SnO_2$계를 들 수 있으며, 이들 중에서 Sn을 $In_2O_3$에 치환고용시킨 ITO박막의 경우, 전기적 및 광학적 특성이 상대적으로 우수하기 때문에 실용화 TCO박막으로서 가장 널리 사용되고 있다. 한편, Flexible display의 경우, 유연성의 폴리머기판위에 증착되는 TCO박막에 대하여 요구되는 특성으로는 높은 투과율 및 낮은 비저항은 물론, 박막표면의 평활도 (낮은 표면조도), bending에 대한 높은 기계적 특성 (낮은 내부응력), 수분침투에 대한 높은 barrier특성 및 저온공정 등을 들 수 있다. 그러나 높은 전기전도도를 가지는 ITO박막을 제작하기 위해서는 $200^{\circ}C$ 이상의 증착온도가 필요하며, 이때 얻어진 다결정의 ITO박막은 높은 표면조도 및 bending시에 낮은 기계적 내구성이 문제점으로 지적되고 있다. 한편, 기판가열 없이 증착한 비정질 ITO박막은 낮은 표면조도, 높은 엣칭속도 및 양호한 식각특성을 나타내지만, 상대적으로 높은 비저항 및 기판과의 낮은 부착력 등이 지적되고 있다. 따라서 본 강연에서는 비정질 ITO박막의 결정화 온도 (약 $160^{\circ}C$) 이상에서도 비정질 구조를 유지하기 때문에 낮은 표면조도와 높은 엣칭속도를 가지면서 상대적으로 전기적 특성과 기계적 내구성이 개선된 새로운 고온형 비정질 TCO박막에 대한 최근의 연구성과를 소개하고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.332.1-332.1
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• 2014

정보통신 기술의 발전으로 지능형 자동차와 같은 미래형 고부가 가치 자동차 산업은 지속적인 성장이 기대된다. 그리고, 안전과 직결되는 차간 거리 계측은 다양한 종류의 센서에 의해 측정이 되고 있으며, 운전자 및 탑승자의 생명을 보호하고 있다. 다양한 차간 거리센서 중에서도 전방의 물체 인식 및 넓은 영역, 장거리에 대한 센싱은 레이저를 이용하여 구현할 수 있다. 본 논문은 자동차 뿐만 아니라, 지능형 자율 주행시 전방의 물체 인식 및 거리 계측 센서로 적용이 가능한 반도체 레이저의 설계 및 제작에 관해 소개한다. 반도체 레이저는 물질에 따라 각각 다른 파장대역의 광을 조사하고 있으며 이 레이저 빔은 물체에 맞고 부딪히면 반사되어 되돌아 오는 특성을 가지고 있다. 따라서, 펄스 구동에 의해 단위 펄스당 출사되는 레이저는 전방 물체에 부딪혀 되돌아 오는 시간을 구하게 되면 레이저 광원에서 물체까지의 거리를 구할 수가 있게 된다. 여기서 펄스 레이저의 출력은 물체 감지가 가능한 거리의 정보를 가지고 있으며, 펄스로 구동될 때 반복 주파수 및 펄스 폭은 각각 거리계측 시간과 분해능을 결정하는 주요 요소가 된다. 따라서, 장거리 물체의 계측과 물체 식별 능력을 높이기 위해서는 반도체 레이저의 출력을 높이고 펄스폭을 줄여서 분해능을 향상하는 것이 필요하다. 또한, 물체 인식 또는 계측 시간을 빠르게 하기 위해서는 고속 주파수로 동작하게 되면 가능해 질 것이다. 본 논문은 1,550 nm 대역의 반도체 레이저를 제작하여 펄스 구동으로 출력과 펄스폭을 측정하였다. 또한, 보다 높은 전류에서 칩 단면의 열화를 방지하기 위한 기술을 적용하여 설계 및 제작된 레이저의 특성을 측정하여 향후, 지능형 자동차의 레이저 레이다(LIDAR)와 같은 응용분야에 많이 활용될 수 있을 것으로 기대한다.

• Analytical Science and Technology
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• v.25 no.4
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• pp.223-229
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• 2012

Analytical signal from ICP was compensated by the light scattering of sample aerosols. Reference scattering signal was generated by a He-Ne or diode laser, monitored for the amount of aerosol producing and used for the compensation of analytical signals. The result showed that significant improvement in precision could be achieved for the short-term signal (within 1 minute) from 3.4% to 0.9% RSD in signal and 14.9% to 4.2% for the long-term (10 minutes) for Be, Pb and Co. This method is very useful not only for the pulse type but for continuous type signals especially when a nebulizer is unstable. To improve long-term precision, higher stability is required in the scattering cell and detector as well as the reduction of noise from the line between a nebulizer and plasma.