• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.50-51
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• 2005

냉간 압연과 열처리 공정을 통해 2축 배향성을 가지는 금속 기판 위에 산화물 박막을 증착 시켜 같은 정도의 2축 배향성을 갖도록 제조된 RABiTS template 위에 YBCO 초전도체를 PLD 방법으로 증착하여 YBCO coated conductor 선재를 제조하였다. RABiTS template은 NiW/$Y_2O_3$/NSZ/$CeO_2$ 구조로 DC reactive sputtering와 PLD 방법에 의해 증착되었다. 모든 공정은 reel-to-reel 방식의 연속 공정으로 이루어졌다. 1m와 10m급의 장선 고온초전도선재를 제조하고, 이에 대한 전기적 특성과 초전도 및 다층 산화물 완충층에 대한 결정성, 표면 특성에 대한 분석을 수행하였다. 그 결과 1m 길이에서 end-to-end 107 A와 10.6m 길이에서 end-to-end 51A의 임계 전류를 획득하였다. 제조된 박막형 선재의 초전도 층과 다층의 산화물 완충층 모두 금속 기판의 결정성을 그대로 유지하면서, epitaxial하게 성장하였으며, 최종 YBCO의 in-plane FWHM 값은 > $9^{\circ}$를 유지 하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.268-268
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• 2006

YBCO 초전도 박막을 제조하기 위해 일반적으로 사용되는 RABiTS공정을 통해 제조된 양축 정렬된 Ni 선재 위에 직접 YBCO를 증착시키려는 시도가 많이 이루어졌다. Ni 위에 직접 증착시킨 YBCO 박막은 c-축으로 정렬되는 온도에서 Ni이 확산되어 YBCO와 반응하여 초전도 물성을 약화시킨다. 이것을 방지하기 위하여 완층층을 먼저 증착을 하는 연구를 시행하였다. 본 연구는 Ni-5at.%W(100) 기판위에 hot-wall type MOCVD (metal organic chemical vapor deposition)를 이용하여 증착을 실시하였다. 완층층으로는 Ni, YBCO와 각각 4.70%, 3.32%의 lattice mismatch를 갖는 $Yb_2O_3$를 선택하였으며, 증착 조건으로는 온도 $800\;{\sim}\;1000^{\circ}C$, 시간 3 ~ 10min, 증착압력 10 Torr의 조건에서 증착을 행하였다. $Yb_2O_3$를 형성하기 위해 산소를 이용하였으나 $Yb_2O_3$(200) 형성을 방해하는 NiO(111)이 형성되었다. 산소를 대신해 수증기를 이용하여 NiO 상이 없는 $Yb_2O_3$(200)을 형성하였다. 증착 시간과 수증기 압력에 따른 $Yb_2O_3$의 $I_{(200)}/(I_{(111)}+I_{(200)})$의 상대 회절강도비를 XRD (X-ray diffraction)를 이용하였고, 증착된 표면 형상은 SEM(scanning electron microscopy)을 통해 관찰하였다.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.245-248
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• 2002

One dimensional conduction equation is solved by finite difference method, to analyse the stability of Au/YBCO film deposited on a sapphire substrate. Jolue heat is included in the case of current sharing state. The analysis shows the quench and recovery of superconductor depending on the amount of thermal disturbance release on the center surface of superconductor. The critical disturbance energies for different filling factor and operating current are calculated.

• Progress in Superconductivity
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• v.14 no.1
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• pp.45-51
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• 2012

Microwave metrology for the thickness of metallic or superconductive films provides a new way to measure the film thickness in a non-invasive way by using microwave resonators, with the measurement accuracy affected by standard uncertainties in the resonator quality factor, temperature-dependent resonant frequency and the dimensions of the resonators. Here we study effects of the standard uncertainty in the thickness, $t_{cal}$, of a calibration $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) film on the measured thicknesses, $t_{RF}$, by using a ~ 40 GHz microwave resonator. For the study, we used five YBCO films having the thicknesses of 70 - 360 nm, for which relative standard uncertainties in $t_{RF}$ due to that in $t_{cal}$ are obtained. The standard uncertainty in $t_{cal}$ was determined with the surface roughness of the film taken into account. It appeared that relative standard uncertainty in $t_{cal}$ significantly affects the $t_{RF}$ values, with the values of 1% (5%) in the former resulting in those of 1-2% (5-9%) for the latter at 10 K. Our results show that, for realizing relative standard uncertainties less than 5% in $t_{RF}$ for all the YBCO films, the surface roughness of the calibration films should be small enough to realize a relative standard uncertainty of less than 2.7% in $t_{cal}$.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.05a
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• pp.59-60
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• 1993

• Progress in Superconductivity
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• v.8 no.1
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• pp.27-32
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• 2006

[$YBa_2Cu_3O_{7-x}$] thin films were deposited on various buffered-templates by a metal organic chemical vapor deposition(MOCVD). Three different templates of $CeO_2/YSZ/CeO_2/pure-Ni(CYC),\;CeO_2/YSZ/Y_2O_3/Ni-3at.%W(YYC)$ and $CeO_2/IBAD-YSZ$/stainless steel were used. The Ni and Ni-W alloy tapes were biaxially textured by cold rolling and annealing heat treatment. The dense YBCO films were grown on both the IBAD and YYC templates with no microcrack, while the YBCO films on the CYC templates were grown with the formation of microcracks and NiO. The YBCO film on the YYC template showed the higher $I_c$ than that on CYC template. Especially, the IBAD templates with a thin $CeO_2$(type I) and thick $CeO_2$(type II) top layer were used to compare the deposition nature of the YBCO on them. Comparing the current property of the YBCO films on IBAD templates, the YBCO film deposited on thick $CeO_2$ layer was better than the film on thin $CeO_2$ layer.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.1998-2000
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• 2005

The effects of the addition of nanocrystalline Y2O3 powder on the microstructure and superconducting properties have been investigated in YBCO films prepared by TFA-MOD process. Precursor solution doped with extra $Y_2O_3$ Powder was prepared by adding $Y_2O_3$ powder into a stoichiometic precursor solution with a cation ratio of Y:Ba:Cu=1:2:3. Coating solutions with and without $Y_2O_3$ doping were coated on $LaAlO_3(100)$ single crystal by a dip coating method, cacination and conversion heat treatments were performed at the controlled atmosphere containing water vapor Current carry capacity(Jc) of YBCO film was enhanced about 50% by $Y_2O_3$ doping. It is thought that the enhancement of Jc is due to the better connectivity of YBCO grains and/or the flux pinning by the presence of nanocrystalline $Y_2O_3$ Particles embedded in YBCO grains.

• 한국초전도학회:학술대회논문집
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• v.15
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• pp.70-70
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• 2005

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.365-367
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• 2002

A serious problem in using YBCO films for fault current limiter is inhomogeneities caused by imperpect manufacturing. So simultaneous quenches are a difficult problem which elements for current limiting are connected in series for increasing voltage ratings. We investigated extended electric field - current characteristics for current limiting element of YBCO film when 0-130mT magnetic field is applied. And quench characteristics were investigated in over all element and between elements of YBCO films. From the experiments, it was shown that applied magnetic fields using solenoid coil induced uniform quench distribution for over all stripes and simultaneous quench in all elements for current limiting of YBCO film was realized.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.80-84
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• 2000

High temperature superconductor shows a good electric and magnetic properties and is known as a good candidate in various electronic device application. At present the technique to construct multilayers composed of HTS films and insulator films has not been fully studied in domestic research institutes. Since the construction of any reasonable eletronic devices require the use of multilayers, the development of HTS eletronic devices has been limited. To manufacture multiplayer, several processing steps which involve deposition and ion millings are required. To manufacture a good quality multilayerd structure, not only the deposition techniques but also the proper patterning have to be developed. In this work, we have fabricated a YBCO/STO/YBCO multiplayer and studied the electronic properties of it.