• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.90-98
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• 1996

We have evaluated the theoretical conversion loss and noise temperature of mixer using the quantum mixer theory and the method to determine the embedding impedance of waveguide-type mixer mount. At fixed backshort position of the mixer, the calculated SSB mixer conversion loss and mixer noise temperature are 5 dB and 10K within frequency range form 85 GHz to 115 GHz, respectively. The SIS mixer has been developed by using through on the calculated rsutls to observe cosmic radio waves. SIS junction of mixer is Nb/Al-AlOx/Nb and it consists of four series array. Area of each of junction is about 2.5${\mu}m^{2}$. The average receiver noise temperature of manufactured receiver with this mixer is about 30 K(DSB). The receiver noise temperature is much lower than that of receiver with a mixer using mechanical tuning backshort.

• Nuclear Engineering and Technology
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• v.38 no.2
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• pp.147-154
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• 2006

Thermal fatigue of the coolant circuits of PWR plants is a major issue for nuclear safety. The problem is especially accute in mixing zones, like T-junctions, where large differences in water temperature between the two inlets and high levels of turbulence can lead to large temperature fluctuations at the wall. Until recently, studies on the matter had been tackled at EDF using steady methods: the fluid flow was solved with a CFD code using an averaged turbulence model, which led to the knowledge of the mean temperature and temperature variance at each point of the wall. But, being based on averaged quantities, this method could not reproduce the unsteady and 3D effects of the problem, like phase lag in temperature oscillations between two points, which can generate important stresses. Benefiting from advances in computer power and turbulence modelling, a new methodology is now applied, that allows to take these effects into account. The CFD tool Code_Saturne, developped at EDF, is used to solve the fluid flow using an unsteady L.E.S. approach. It is coupled with the thermal code Syrthes, which propagates the temperature fluctuations into the wall thickness. The instantaneous temperature field inside the wall can then be extracted and used for structure mechanics computations (mainly with EDF thermomechanics tool Code_Aster). The purpose of this paper is to present the application of this methodology to the simulation of a straight T-junction mock-up, similar to the Residual Heat Remover (RHR) junction found in N4 type PWR nuclear plants, and designed to study thermal striping and cracks propagation. The results are generally in good agreement with the measurements; yet, in certain areas of the flow, progress is still needed in L.E.S. modelling and in the treatment of instantaneous heat transfer at the wall.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.12
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• pp.39-46
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• 1996

In AlGaAs/GaAs HBT the temperature dependence of DC parameters was investigated over the temperature range between 95K and 580K. The temperature dependence of DC parameters depends on the relative contribution of each of the current components suc as emitter-injection-current, base-injection-current, bulk recombination current, interface recombination curretn, thermal generation ecurrent and avalanche current due to impact ionization within the collector space charge layer in a specific temperature. In this paper we investigated the temperature effects on DC parameters such as V$_{BE,ON}$ current gain, input and output characteristics, V$_{CE, OFF}$, R$_{E}$, R$_{C}$ and analyzed the origins, and extracted the qualitativ econditions for a stable HBTs against the temperature variation. Finally, in order to keep HBTs stable with respect to the variation of temperature, the valance-band-energy-discontinuity at emitter-base heterojunction should be large enough to enhance the effect of carrier suppression at a relatively high temperature. In addition the recombination centers, especially around collector junction, should be removed and the area of emitter and collector junction should be identical as well.

• Progress in Superconductivity
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• v.3 no.1
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• pp.74-77
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• 2001

We have fabricated a high-Tc superconductive transistor with polyvinylidene fluoride (PVDF) gate electrode on MgO bicrystal Josephson junction by spin-coating method. The PVDF ferroelectric film is found to be suitable fur a gate electrode of the superconductive transistor since it has not only small leakage current but also high dieletric constant at low temperature. For the application of superconducting-FET, we investigated millimeter wave properties (60 GHz band) of the Josephson junction with PVDF gate electrode.

• Korean Journal of Optics and Photonics
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• v.23 no.2
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• pp.64-70
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• 2012

We analyzed the changes in electrical and optical characteristics of 1 $mm^2$ multiple-quantum-well (MQW) blue LEDs grown on a c-plane sapphire substrate after a stress test. Experiments were performed by injecting 50 mA current for 200 hours to TO-CAN packaged sample chips. We selected the value of injection current for stress through the junction-temperature measurement by using the forward-voltage characteristics of a diode to maintain a sufficiently low junction temperature during the test. The junction temperature at the selected injection current of 50 mA was 308 K. Experiments were performed under the assumption that the average junction temperature of 308 K did not affect the characteristics of the ohmic contact and the GaN-based materials. Before and after the stress test, we measured and analyzed current-voltage, light-current, light distribution on the LED surface, wavelength spectrum and relative external quantum efficiency (EQE). After the stress test, it was observed experimentally that the optical power and the relative EQE decreased. We theoretically investigated and experimentally proved that these phenomena are due to the increased nonradiative recombination rate caused by the increased defect density.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.326-336
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• 1997

From the concept that the ion implantation-induced defect is one of the major factors in determining source/drain junction characteristics, high quality ultra-shallow $p^+$-n junctions were formed through the control of ion implantation-induced defects in silicon substrate. In conventional process of the junction formation. $p^+$ source/drain junctions have been formed by $^{49}BF_2^+$ ion implantation followed by the deposition of TEOS(Tetra-Ethyl-Ortho-Silicate) and BPSG(Boro-Phospho-Silicate-Glass) films and subsequent furnace annealing for BPSG reflow. Instead of the conventional process, we proposed a series of new processes for shallow junction formation, which includes the additional low temperature RTA prior to furnace annealing, $^{49}BF_2^+/^{11}B^+$ mixed ion implantation, and the screen oxide removal after ion implantation and subsequent deposition of MTO (Medium Temperature CVD oxide) as an interlayer dielectric. These processes were suggested to enhance the removal of ion implantation-induced defects, resulting in forming high quality shallow junctions.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.6
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• pp.772-777
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• 2018

This paper used RF Magnetron Sputtering to deposition n-type and p-type to ITO glass. The N-type ohmic contact worked well under all conditions. Sheet resistance has been shown to increase sheet resistance as RF Power increases. After analyzing the surface of the deposited thin film, in the condition that RF Power was 250W and substrate temperature was $250^{\circ}C$, particles were measured to have a uniform and consistent thin film. P-type has good ohmic contact under all conditions and sheet resistance has been shown to increase as RF Power increases. As the RF Power grew, thickness increased and stabilized. PN junction thin film and NP junction thin film showed increased thickness and stabilized as sputtering time increased. As a result of thin film, conversion efficiency was at 0.2 when sputtering time was 10 minutes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.10
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• pp.1-8
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• 2014

Heat dissipation of the high power LED is a critical issue. To estimate the junction temperature of the LED chip is most important in characterizing the heat dissipation, but it is impossible to directly measure it. In this study, surface temperatures of the 12.8W LED bulb was measured for 5 points using a data logger and compared with the simulated results using a thermal simulator based on FVM (finite volume method) to secure a reliability of the simulation. Effects of some factors such as lens, emissivity and air inlet were investigated using simulation works and then the results were analysed.

• Ceramist
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• v.22 no.2
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• pp.146-169
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• 2019

To overcome the theoretical efficiency of single-junction solar cells (> 30 %), tandem solar cells (or multi-junction solar cells) is considered as a strong nominee because of their excellent light utilization. Organic-inorganic halide perovskite has been regarded as a promising candidate material for next-generation tandem solar cell due to not only their excellent optoelectronic properties but also their bandgap-tune-ability and low-temperature process-possibility. As a result, they have been adopted either as a wide-bandgap top cell combined with narrow-bandgap silicon or CuIn_xGa_(1-x)Se₂ bottom cells or for all-perovskite tandem solar cells using narrow- and wide-bandgap perovskites. To successfully transition perovskite materials from for single junction to tandem, substantial efforts need to focus on fabricating the high quality wide- and narrow-bandgap perovskite materials and semi-transparent electrode/recombination layer. In this paper, we present an overview of the current research and our outlook regarding perovskite-based tandem solar technology. Several key challenges discussed are: 1) a wide-bandgap perovskite for top-cell in multi-junction tandem solar cells; 2) a narrow-bandgap perovskite for bottom-cell in all-perovskite tandem solar cells, and 3) suitable semi-transparent conducting layer for efficient electrode or recombination layer in tandem solar cells.

• Nuclear Engineering and Technology
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• v.38 no.3
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• pp.293-300
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• 2006

A liquid metal reactor (LMR) operated at high temperatures is subjected to both cyclic mechanical loading and thermal loading; thus, creep-fatigue is a major concern to be addressed with regard to maintaining structural integrity. The Korea Advanced Liquid Metal Reactor (KALIMER), which has a normal operating temperature of $545^{\circ}C$ and a total service life time of 60 years, is composed of various cylindrical structures, such as the reactor vessel and the reactor baffle. This study focuses on the creepfatigue crack initiation for a cylindrical Y-junction structure made of 316 stainless steel (SS), which is subjected to cyclic axial tensile loading and thermal loading at a high-temperature hold time of $545^{\circ}C$. The evaluation of the considered creep-fatigue crack initiation was carried out utilizing the ${\sigma}_d$ approach of the RCC-MR A16 guide, which is the high-temperature defect assessment procedure. This procedure is based on the total accumulated strain during the service time. To confirm the evaluated result, a high-temperature creep-fatigue structural test was performed. The test model had a circumferential through wall defect at the center of the model. The defect front of the test model was investigated after the $100^{th}$ cycle of the testing by utilizing a metallurgical inspection technique with an optical microscope, after which the test result was compared with the evaluation result. This study shows how creep-fatigue crack initiation for a high-temperature structure can be predicted with conservatism per the RCC-MR A16 guide.