• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.30-33
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• 2003

YBCO coated conductor, also called the 2nd generation high temperature superconducting wire, consists of oxide multi-layer hetero-epitaxial thin films. Pulsed laser deposition (PLD) is one of many film deposition methods used to make coated conductor, and is the one known to be the best to make superconducting layer so far. As a part of the effort to make long length coated conductor, the optimum deposition condition of YBCO film on single crystal substrate (SrTiO3) was investigated using PLD. Substrate temperature, oxygen partial pressure, and laser fluence were varied to find the best combination to grow high quality YBCO film.

• Progress in Superconductivity and Cryogenics
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• v.7 no.3
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• pp.5-8
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• 2005

Superconducting YBCO films were successfully fabricated by MOD process using F-free Cu precursor solution. In this study. a chemically modified precursor solution for MOD Processing was synthesized using metal-organic salts and F-free Cu precursor. It was shown that crack-free and uniform precursor films were formed after calcination in humidified oxygen atmosphere. Less than 3 hours are required to finish the calcination process. XRD measurement shows that $BaF_2,\;CuO,\;Y_2O_3$ are major constituent of precursor films. Furthermore. YBCO films without any secondary phases were successfully fabricated after annealing in wet $Ar/O_2$ prepared on a $LaA1O_3$ single crystal substrate $(10mm{\times}10mm)$ gives transport Ic of 10A at 77K. This chemical modification approach is a possible candidate for improving MOD-processing of YBCO coated conductor.

• Proceedings of the KIEE Conference
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• summer
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• pp.806-808
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• 2004

The series and parallel connection is essential for increasing power ratings of resistive type for fault current limiters. To increase voltage class, components are connected in series and to increase current level to the nominal value, they are connected in parallel. There are two ways to connect components in series and parallel. First, connected in series and then the module connects to the parallel. Second, connected in parallel and the module connects to the series. We have studied for the two ways. In this paper, we particularly investigated way to connect components in parallel first This way has the advantage of inducing effective simultaneous quench without any other devices, for example, the thing which is inducing magnetic field to the limiting and shunt resistors. And also we studied for the endurance of component which is patterned to the bi-spiral for prospective fault current. It is very important to understand this, because SFCL will use as the only device to decrease burden of circuit breaker. As experimental results, limiting component patterned to bi-spiral endures fault current up to 30kA and it works well, in parallel to series connection,

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.278-280
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• 2001

BSCCO thin films have been fabricated by co-deposition at an ultralow growth rate using ion beam sputtering(IBS) method. The growth rates of the films was set in the region from 0.17 to 0.27 nm/min. MgO(100) was used as a substrate. In order to appreciate stable existing region of Bi 2212 Phase with temperature and ozone pressure, the substrate temperature was varied between 655 and 820$^{\circ}C$ and the highly condensed ozone gas pressure(PO$_3$) in vacuum chamber was varied between 2.0x10$\^$-6/ and 2.3x10$\^$-5/ Torr. Bi 2212 Phase appeared in the temperature range of 750 and 795$^{\circ}C$ and single phase of Bi 2201 existed in the lower region than 785$^{\circ}C$. Whereas, PO$_3$ dependance on structural formation was scarcely observed regardless of the pressure variation. And high quality of c-axis oriented Bi 2212 thin film with T$\sub$c/(onset) of about 70 K and T$\sub$c/(zero) of about 45 K is obtained. Only a small amount of CuO in some films was observed as impurity, and no impurity phase such as CaCuO$_2$ was observed in all of the obtained films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04a
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• pp.39-42
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• 2004

The $Bi_2Sr_2Ca_nCu_{n+1}O_x$ superconducting thin film fabricated by using the sputtering method was compared with the $Bi_2Sr_2Ca_nCu_{n+1}O_x$ superconducting thin film fabricated by using the evaporation method. In doing the ultra-low deposition because each element can exist on the substrate surface, both the sputtering method and the evaporation method could easily fabricate single phase of the Bi2212 phase. Also, it is cofirmed that by optimizing the deposition condition, each single phase of the Bi2201 phase and the Bi2212 phase can be fabricated, the sticking coefficient of Bi element is clearly related to the changing of substrate temperature and the formation of the Bi2212 phase.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2001-2003
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• 2005

Various organic acid were used in order to prepare new metalorganic deposition solution for high quality $REBa_2Cu_3O_{7-{\delta}}$ (RE=Y, Eu, Gd) films. Prepared fluorine free MO precursor solution was coated on single crystal (001) $LaAlO_3$ (LAO) by dip coating method. Processing parameters such as oxygen partial pressure, water vapor, ramping rate and pyrolysis temperature etc havebeen controlled in order to make high $J_c$ films with a good epitaxial relationship with substrate. 0.5 micron-thick film was obtained by single coating and no crack appeared after calcination. Oxygen partial pressure was varied in the range of $100{\sim}1,000 ppm$ and conversion heat treatment was carried out at the temperature of $725{\sim}765^{\circ}C$. A critical transition temperature $(T_{c0})$ of 90K and a critical transport current density $(J_c)$ of $>0.5MA/cm^2$ (77K and self-field) were demonstrated for the YBCO film on (001) oriented LAO substrates with a thickness of 0.5 micron. $I_c$ was determined by utilizing a transport measurement. SEM and XRD investigations confirmed that films were grown epitaxially onto the LAO single crystal substrate. It is thought that fluorine free new MOD solutionis promising for high quality REBCO films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.503-504
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• 2007

$Bi_2Sr_2Ca_{n-1}Cu_nO_x$(n=0, 1, 2)superconducting thin films have been fabricated by atomic layer-by-layer deposition at an ultra low growth rate using IBS(Ion Beam Sputtering) method. During the deposition, 90 mol% ozone gas of typical pressure of $1{\sim}9{\times}10^{-5}$ Torr are supplied with ultraviolet light irradiation for oxidation. XRD and RHEED investigations reveal out that a buffer layer with some different compositions is formed at the early deposition stage of less than 10 units cell and then Bi-2201 oriented along the c-axis is grown.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.236-237
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• 2007

Lamination of coated conductor is important to commercialize for electrical stabilizer and mechanical support. It should be known the properties of soldering interface and the variation of superconductivity on coated conductor with various kinds of solders. $SmBa_2Cu_O_x$ thin films were deposited by co-evaporation method (EDDC, Evaporation using Drum in Dual Chambers). 4 kinds of solders were used to investigate interface properties of SmBCO conductors. In-Bi solder could maintain good connection.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.259-262
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• 2003

Superconducting flux flow transistor(SFFT) is based on a control of the Abrikosov vortex flowing along a channel. The induced voltage by moving of the Abrikosov vortex in SFFT is greatly affected by the thickness and width, of channel. In order to fabricate a reproducibility channel in SFFT, we have researched the variation of the critical characteristics of YBCO thin films with the etching time using ICP(Inductively coupled plasma) system. It was certified that the velocity of vortex decreased with increasing the width of channel and was saturated faster in low bias from a simulation. An etching mechanism of YBCO thin films by ICP system was also certified by AFM(Atomic Force Microscope) and by measuring the critical current density with etching time. As measurement result, we could analyze that we should optimize the etching thickness of channel part to construct a flux flow transistor with desired characteristics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.268-269
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• 2005

YBCO 박막형 초전도체(coated conductor) 제조를 위해서는 여러 층의 완충층이 필요하다. 현재 일반적인 완충층의 구조는 seed layer로써 $Y_2O_3$, diffusion barrier로 YSZ, capping layer로 $CeO_2$가 사용되고 있다. 특히, capping layer로 $CeO_2$는 YBCO와 lattice mismatch가 매우 우수한 산화물로 이용되고 있다 본 연구에서는 $CeO_2$ capping layer가 증착 방법에 따라 그 위에 증착되어지는 초전도층의 특성에 어떤 영향을 미치는지 연구하였다. $CeO_2$를 thermal evaporation과 PLD (pulsed laser deposition) 증착 방법으로 증착 한 후 그 위에 PLD 방법으로 YBCO를 증착하여 coated conductor의 성능을 평가하였다.