• Progress in Superconductivity
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• 제1권1호
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• pp.31-35
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• 1999

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-$T_c$ superconducting (HTS) $YBa_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed on the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height, t/h. The spread of step-edge junction parameters was measured from each 13 junctions with t/h=1/3, 1/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K.

• Progress in Superconductivity
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• 제3권1호
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• pp.120-124
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• 2001

To establish the deposition condition of YBCO thin film on MgO single crystal substrates, processing parameters of deposition temperature, chemical composition and oxygen partial pressure were controlled. When using a Ba-deficient composition of YB $a_{1.8}$ $Cu_3$$O_{x}$, non-superconducting phase like CuO, $CuYO_2$ were formed, but BaCu02 was formed together with Yl23 phase when the starting composition was Ba-rich ($YBa_{2.3}$ $Cu_3$ $O_{x}$). The epitaxially grown Yl23 phase was formed at 760-$810^{\circ}C$ and $P_{O2}$=0.29-0.91 Torr.r.r.r.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.287-290
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• 2003

For microwave device applications, c-axis oriented high temperature superconducting YBa$_2$Cu$_3$O$_{7-{\delta}}$ (HTS-YBCO) epitaxial thin films on the r-cut sapphire substrate(Al$_2$O$_3$) were prepared. In order to reduce the lattice mismatch with a substrate and to enhance the crystallity of HTS thin films, CeO$_2$ buffer layer on the r-cut sapphire substrate was grown by the RF-magnetron sputtering. The YBCO films on the CeO$_2$ buffer layer were deposited using the pulsed-laser deposition (PLD) method. These HTS YBCO /CeO$_2$/Al$_2$O$_3$ multilayer thin films(30 $\times$ 30 mm$^2$) routinely exhibited a critical temperature(T$_{c}$) of 89 K from the R-T measurement. Using HTS YBCO/CeO$_2$ /Al$_2$O$_3$ multilayer thin film. We fabricated and characterized the microwave passive devices (planar type filters) with cryopack-age such as the coupled -line type low-pass filter (LPF) and the open-loop meander type bandpass filter (BPF).filter (BPF).).

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.88-91
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• 2003

The crystal structure and properties of YBa$_2$Cu$_3$$O_{7-x}$(YBCO) and CeO$_2$ thin films deposited on r-plane (1(equation omitted)02) sapphire substrate by pulsed- laser deposition(PLD) have been investigated. C-axis oriented epitaxial YBCO thin films with critical temperature (Tc) of 88 K were routinely grown on (200) oriented CeO$_2$ buffer layers with thickness in the range between 20 to 80 nm. When the thickness of the (200)oriented CeO$_2$ buffer layer increases over than 80 nm, the superconducting properties of YBCO thin films on that were deteriorated. The decrease in Tc of YBCO thin films was explained by the microcrack formation in CeO$_2$ buffer layer. These results indicate that the thickness of the (200) oriented CeO$_2$ buffer layer is critical to the epitaxial YBCO thin nim growth on r-plane (1(equation omitted)02) sapphire substrate.e.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.129-132
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• 2003

Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition (MOCVD) technique using single liquid source for the application of YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (100) single crystal MgO substrate was used for searching deposition condition. Bi-axially oriented CeO$_2$ and NiO films were fabricated on {100}〈001〉 Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660~80$0^{\circ}C$) and oxygen flow rates (100~500 sccm) were changed to find the optimum deposition condition. The best (100) oriented YSZ film on MgO was obtained at 74$0^{\circ}C$ and $O_2$ flow rate of 300 sccm. For YSZ buffer layer with this deposition condition on CeO$_2$/Ni template, full width half maximum (FWHM) values of the in-plane and out-of-plane alignments were 10.6$^{\circ}$ and 9.8$^{\circ}$, respectively. The SEM image of YSZ film on CeO$_2$/Ni showed surface morphologies without microcrack.k.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권7호
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• pp.375-381
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• 2000

In this paper, we described the characterization of High-Tc Superconducting(HTS) microstrip antenna using non-radiating edge feeding technique and reported the microwave properties of HTS antennas with temperature. To do this, we prepared the $YBa_2Cu_3O_{7-x}$ superconducting thin film on MgO substrate using pulse-laser deposition techniques. The HTS microstrip antenna using non-radiating feeding technique was fabricated using chemical wet-etching. Then it was compared with identical antenna patterned with evaporated gold. The diverse measured results have been reported in terms of the input impedance, resonant frequency and return loss. In additional, at around the critical temperature, the effect of kinetic inductance which affect the resonant characteristic of the HTS microstrip antenna was reported.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 기술교육전문연구회
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• pp.20-23
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• 2003

The operational characteristics of flux-lock type high-Tc superconducting fault currentlimiters(HTSC-FCLs) was described and currents equation at each coil was derived from equivalent circuit. $YBa_{2}Cu_{3}O_{7-x}$(YBCO) thin film was used as the current limiting elements of the flux-lock type HTSC-FCL, which were fabricated by etching the YBCO thin film into 2 mm wide and 420 mm long meander line consisting of foureen stripes with different length. The 2nd peak on the current of coil 2 after a fault disappeared by current of the 3rd winding, which was installed in the flux-lock type HTSC-FCL.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 영호남 합동 학술대회 및 춘계학술대회 논문집 센서 박막 기술교육
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• pp.146-148
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• 2006

The quench characteristics of flux-lock type high-Tc superconducting fault current limiters(SFCL) was investigated, $YBa_2Cu_3O_{7-x}$(YBCO) thin film was used as the current limiting elements of the flux-lock type SFCL. The quench characteristics of current limiting elements consisting of the flux-lock type SFCL was more improved than that of the resistive type SFCL.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 영호남 합동 학술대회 및 춘계학술대회 논문집 센서 박막 기술교육
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• pp.77-81
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• 2006

We report the performance of a four-element, 11.67 GHz, high-Tc superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system. Our array antennas were designed and built on a 0.5 mm thick MgO substrate. To compare the superconducting antennas with normal conducting counterpart, One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from $YBa_2Cu_3O_{7-x}$ (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperature. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was 35.79 dB at the resonant frequency of 11.67 GHz and The total effective bandwidth was about 3.4 %. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the HTS antenna array for circularly polarization.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2003년도 춘계학술연구발표회
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• pp.12-12
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• 2003

초전도 선재로의 응용을 위하여 Pulsed laser deposition(PLD)법으로 고온 초전도 체 YBa₂Cu₃O/sub 7-δ/(YBCO) coated conductor를 제조하였다. coated conductor는 금속기판/완충층/초전도층의 구조를 이루고 있는데 완충층은 금속 기판의 집합조직을 초전도층까지 전달하는 역할과 금속기판의 금속이 초전도층으로 확산되어 초전도층의 전기적 특성을 열화시키는 것을 막아주는 확산장벽으로의 역할 등을 수행한다. 완충층의 박막 성장이 제대로 이루어지지 않으면 우수한 초전도 특성을 가지는 초전도층을 얻을 수 없다. 완충층은 금속기판과의 lattice match, thermal match등이 요구되고, 화학적으로 금속기판 및 초전도층과 반응하지 않아야 하며, 긍속기판의 산화없이 epitaxial하게 박막증착이 이루어질 수 있는 재료이어야 한다. 이러한 조건을 만족하는 YBCO, CeO₂, YSZ 등이 주로 사용되고 있다. 전기연구원에서 YBCO coated conductor 선재를 제조하기 위하여 사용하고 있는 다층 박막의 구조는 YBCO/CeO₂/YSZ/CeO₂/Ni(002)과 YBCO/CeO₂/YSZ/Y₂O₃/Ni(002)이며, 최적의 증착조건을 찾기 위하여 성장시 챔버의 산소분압, 완충층의 두께, 기판 온도 등을 변화시켰다. 증착된 완충층 및 초전도층의 집합 조직은 D8-Discover with GADDS(General Area Detector Diffraction System)로 XRD분석을 했고, 미세구조는 SEM으로 관찰하였으며 4단자법을 이용하여 초전도 특성을 측정하였다.