• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2004년도 High Temperature Superconductivity Vol.XIV
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• pp.95-95
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• 2004

• 한국전기전자재료학회논문지
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• 제18권11호
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• pp.1061-1067
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• 2005

The resonant frequency modulation of $YBa_2Cu_3O_{7-x}$ meander lines has been investigated as functions of optical pulse energy and temperature by using a network analyzer. The frequency-domain measurements are performed by controlling both the resonant frequency and the frequency width. The meander lines, configured in a microstrip geometry, are illuminated by optical pulses from an actively mode-locked Nd:YAG laser. The variation of the resonant frequency shows a quadratic dependence on the reduced optical pulse energy $P/P_c$, where $P_c$ is defined as the critical optical pulse energy at which resonance signal has disappeared. As for the dependence on temperature, the results are in good agreement with the previously reported data.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.77-79
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• 2003

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.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.91-94
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• 1999

A new type of high-T$_c$ superconducting Josephson junctions has been prepared by Ar ion beam etching and electron beam lithography. YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on (001) SrTiO$_3$ single crystal substrate by pulsed laser deposition were patterned by Ar ion milling with photolithography. The narrow slit with a electroresist mask, about 1000 ${\AA}$ wide, was constructed over a 3 ${\sim}$ 5 ${\mu}$m bridge of a 1200-${\AA}$-thick YBCO film by electron beam lithography. The slit was then etched by the Ar ion beam to form a damaged 600-${\AA}$-thick YBCO. Thus prepared structure forms an S-N-S (YBCO - damaged YBCO - YBCO) type Josephson junctions. Those junctions exhibit RSI-like I-V characteristics at 77 K. The properties of the Josephson junctions such as I$_c$ R$_N$, and J$_c$ were characterized.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1995년도 춘계학술대회 논문집
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• pp.234-238
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• 1995

In this parer, by means of adding nonsuperconductive phase sliver into YBCO matrix, the superconductivity of Melted Texture Growth (MTG) YBa$_2$Cu$_3$O$\_$7-x/ was improved remarkably. In order to eliminate the crack inthe YBCO and the weak linkin the grain boundary, Ag contents from 2wt% to 18Wt% were doped in the YBCO It was found that J$\_$c/ of YBCO increase with the increasing Ag content till 14 wt% over 14wt% of Ag content, the Jc tends to stable . The grain size of YBCO became fine when Ag was added in the YBCO and X-ray diffraction showed that the YBCO crystal prepared by the above technique had (001) orientation and growing plane of YBCO was a-b plane. Using Bens medel, the J$\_$c/ was calculated and the best result was J$\_$c/ 76000A$\textrm{cm}^2$(77K, 100Gs).

• 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.

• Progress in Superconductivity
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• 제5권1호
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• pp.75-79
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• 2003

YBCO films were deposited with various thicknesses from 100nm to 1.6$\mu\textrm{m}$ on single crystal $SrTiO_3$ substrates by pulsed laser deposition (PLD). The effects of different deposition conditions, especially different deposition rates by means of changing the pulsed laser frequency up to 200Hz, on the J$_{c}$ value were studied. For YBCO film with the thickness of 200nm, the $J_{c}$ value of $2.1MA/\textrm{cm}^2$ has been achieved under the high deposition rate of 3.2nm/s (190nm/min). The $J_{c}$ can be maintained greater than $1M/\textrm{cm}^2$ with the thickness less than 1$\mu\textrm{m}$. The X-ray analysis was used to examine the texture, crystallization and surface quality. The SEM was employed to analyze the surface of YBCO, and it was shown the surface of YBCO film became rougher with increasing the thickness. There were many large singular outgrowths and networks of outgrowths on the surface of YBCO films which lowered the density of thick YBCO film. The outgrowth network was probably the a-axis YBCO corresponding to XRD $\theta$-2$\theta$scan and $\chi$-scan which were used to characterize a-axis orientation of YBCO film. The reason for J$_{c}$ declining with increasing the thickness was studied and discussed.sed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1549-1551
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• 1998

We have designed and developed narrow bandpass multipole filters for satellite communication using $YBa_2Cu_3O_{7-x}$(YBCO) thin films on MgO substrates. The superconducting film used in this study was prepared by laser ablation on one side polished MgO (100) substrates. A Nd:YAG laser was used to fabricate YBCO thin films. The wave length of the laser was 355 nm. The laser beam was focused onto a YBCO target rotating linearly to avoid deep craters that may eject macroscopic YBCO particles. The YBCO films were grown at $750^{\circ}C$ in the oxygen partial pressure of 200 mTorr. The deposited YBCO thin films were patterned by conventional wet-etching method. The transition temperatures of YBCO thin films were 85 - 88 K and the film thicknesses were about 5,000 $\AA$. By comparing the performances of normal-metal filters and YBCO filters, we observed that superconducting YBCO multipole filters have been showed superior performances at 77 K.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1590-1592
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• 1999

We have fabricated good quality superconducting $YBa_2Cu_3O_{7-{\delta}}$ thin films on Hastelloy(Ni-Cr-Mo alloys) with $CeO_2$ buffer layers by in-situ pulsed laser deposition in a multi-target processing chamber. Using one of electrical properties of YBCO superconducting which the resistance approaches to zero dramatically on transition temperature, we have researched to make power transmission line, we have deposited YBCO thin film on flexible metallic substrate. However, it is difficult to make films on flexible metallic substrates due to both interdiffusion problem between metallic substrate and superconducting layer and non-crystallization of YBCO on amorphous substrate. From early research, two ways-using textured metallic substrate and buffer layer-were proposed to overcome theses difficulties. We have chosen $CeO_2$ as a buffer layer which has cubic structure of $5.41{\AA}$ lattice parameter and only 0.2% of lattice mismatch with $3.82{\AA}$ of a-axis lattice parameter of YBCO on (110) direction of $CeO_2$. In order to enhance the crystallization of YBCO films on metallic substrates we deposited $CeO_2$ buffer layers at varying temperature $700^{\circ}C$ to $800^{\circ}C$ and $O_2$ pressure. By X-ray diffraction, we found that each domination of (200) and (111) orientations were strongly relied upon the deposition temperature in $CeO_2$ layer and the change of the domination of orientation affects the crystallization of YBCO upper layer.

• 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.