• 한국표면공학회지
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• 제29권5호
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• pp.415-423
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• 1996

Thin film technologies for fabricating SQUIDs involve etching and deposition procedures with the proper substrate materials and $YBa_2Cu_3O_{7-d}$ (YBCO) as the high $T_c$ superconductor. YBCO were prepared on various substrates of MgO, $SrTiO_3$, and $LaAlO_3$ by using off-axis magnetron sputtering methods and annealing in-situ. The parameters of film fabrication processes had been optimized to yield good quality films in terms of the critical temperature $T_c$ and the critical current density $J_c$. The optimized processes yielded $T_C$>90K along with $J_c$>$10_6A$$extrm{cm}^2$ at 77K and>$2\times10_7A/Cm^2$ at 5K. We fabricated step-edge type dc-SQUIDs and directly coupled magnetometers, producing step edges on MgO(100) substrates by etching with Ar-ion beam, depositing YBCO material on them, then patterning them by using ion-milling technique. Circuitizing washer-shape SQUIDs to possess a pair of step-edge junctions of 2-5$\mu$ line width with a high angle>$50^{\circ}C$ , we examined their I-V characteristics thoroughly and Shapiro steps clearly as we irradiate microwaves of 8-20 GHz frequency.

• Progress in Superconductivity
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• 제3권2호
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• pp.163-167
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• 2002

We have fabricated planar-type single-layer second-order high-Tc SQUID gradiometers. The devices consisted of symmetrically designed three parallel-connected square pickup loops that were directly coupled to the SQUID. $YBa_2$$Cu_3$$O_{7}$ film was deposited on $SrTiO_3$ substrate by a PLD system and patterned into a device by the photolithography with ion milling technique. Junctions of the SQUID were either step-edge or bicrystal type. All the structures were formed on a 10 mm $\times$ 5 mm substrate. Balancing of the gradiometer was achieved by adjusting the width of the central pickup loop. The gradiometer noise was measured both inside and outside a magnetically shielded room. Details of the results will be discussed.

• 대한화학회지
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• 제36권1호
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• pp.16-23
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• 1992

고온초전도체 $YBa_2Cu_3O_{7-{\delta}}$에서 Y를 Eu로 치환시킨 $(Y_{1-x}Eu_x)Ba_2Cu_3O_{7-{\delta}}$ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0)를 제조한 후 물성변화를 관찰하였다. X-선 회절분석결과 모든 시료가 사방정계 구조를 갖고 있었으며 x값이 증가함에 따라 격자상수 a, b 및 c도 증가하였다. 전기저항과 자화율측정으로부터 순수한 90K 이상의 고온초전도상이 생성되었음을 알았으며, x값이 커짐에 따라 임계온도가 상승하였다. 주사전자현미경을 사용하여 구한 낟알크기와 자화측정결과로부터 각각의 시료들에 대한 부피 반자성자화율을 구하였으며, x값이 커질수록 이 값은 감소하였다. Eu의 농도가 증가함에 따라 결정격자내의 Ba의 양이 감소됨을 EPMA로 확인하였으며, 이것은 부피반자성 자화율의 감소에 직접적인 영향을 주는 것으로 판단된다.

• Progress in Superconductivity
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• 제9권1호
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• pp.91-95
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• 2007

[ $YBa_2Cu_3O_{7-{\delta}}$ ] films have been prepared on $LaAlO_3$ (100) single-crystal substrates by the metal organic deposition using dichloroacetate precursors (DCA-MOD). DCA precursor solutions with different composition such as; Yttrium-excess(15 at%), barium-poor(25 at%), and a stoichiometric(Y:Ba:Cu=1:2:3) were prepared in order to investigate the effects of precursor composition on the properties of YBCO films prepared by DCA-MOD method. Coated films were calcined at low temperature up to $500^{\circ}C$ in flowing humid oxygen atmosphere. Conversion heat treatment was performed $800^{\circ}C$ for 2 h in flowing Ar gas containing 1000 ppm oxygen with a humidity of 9.45%. For the film prepared using excess yttrium composition, high critical current density ($J_c$) of $>2MA/cm^2$ was obtained whereas, for the films prepared using barium-poor composition, $J_c$ was lower than $1MA/cm^2$.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권7호
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• pp.282-287
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• 2003

″H″ type resonator has the advantage for the miniaturization of high-T7 superconducting (HTS) microstrip antenna in comparison with the conventional microstrip antenna such as rectangular type or circular type. In this paper we designed miniaturized HTS antennas using this "H"-type resonator and reported the characteristics of our antennas including return loss, bandwidth, radiation patterns, efficiency and so on. To fabricate the "H" type antenna, HTS YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) thin films were deposited on MgO substrates using rf-magnetron sputtering. For comparison between normal conducting antennas and superconducting antennas, the gold antennas with the same dimension were also fabricated. An aperture coupling was used for impedance matching between 50 $\Omega$ feed line and HTS radiating patch. The ″H" type superconducting antenna showed the performance of 1.38 in SWR, 26 % in efficiency, and 13.8 dB in the return loss superior to the normal conducting counterpart.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.132-135
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• 2000

Magneto-resistances of the YBa$_2$Cu$_3$O$_{7-{\delta}}$ based coated conductors fabricated on the tilted single crystalline Ni substrates and RABiTS (rolling assisted bi-axially textured substrate) were measured under various magnetic fields. The activation energies of vortices were estimated from them by fitting equation of p = p$_o$ exp(-U(H,T)/k$_B$T). When currents flew in the rolling direction for the case of the tilted single crystalline YBCO on the RATS, the activation energies were similar to those of c-axis normal YBCO films on the SrTiO$_3$ single crystal substrates [5] and were slightly larger than those of the RABiTS coated conductors. On the contrary, for the currents flowing in the transverse direction, the magnetoresistances show double transitions in the temperature with much smaller activation energies.

• 한국초전도ㆍ저온공학회논문지
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• 제21권4호
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• pp.9-12
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• 2019

We performed Raman spectroscopy on two different over-doped Bi₂Sr₂CaCu₂O_8+x (BSCCO), of which superconducting transition temperatures are 89 K and 77 K. Line-shape analysis of the Raman-spectrum was done, focused on B_1g bond buckling mode which have drawn a lot of attention, since photoemission studies showed an evidence for strong coupling between the mode and electron. The line-shapes show asymmetry and are well fitted by the Fano line-shape formula. Remarkably, we found that the peak line-widths from B_1g bond buckling mode in BSCCO show much broader than those in YBa₂Cu₃O_7-x. The broad line width can be attributed to the superstructure modulation of BSCCO. Our results imply that B_1g bond buckling mode may have close relation to the origin of superconductivity or to boosting the superconducting transition temperature in BSCCO.

• 한국초전도ㆍ저온공학회논문지
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• 제6권3호
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• pp.6-11
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• 2004

YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) films were deposited on MgO(100) and SrTiO$_3$(100) single crystal substrates by cold-wall type MOCVD method using continuous source supplying system. Under the deposition temperature of 740∼76$0^{\circ}C$, c-axis oriented YBCO films were obtained. In case of the YBCO films deposited on MgO (100) single crystal substrate, the critical temperature (T$_{c}$) was under 81 K regardless of the deposition conditions, whereas T$_{c}$ of the YBCO films deposited on SrTiO$_3$(100) single crystal substrate was 83∼84 K. The critical current (I$_{c}$) of the YBCO film deposited on SrTiO$_3$(100) single crystal substrate for 30 min was 49 A/cm-width and the critical current density (J$_{c}$) was 0.82 MA/$\textrm{cm}^2$ to film thickness of 0.6 ${\mu}{\textrm}{m}$. I$_{c}$ increased to 84.4 A/cm-width as the deposition time increased to 50 min, but J$_{c}$ decreased to 0.53 MA/$\textrm{cm}^2$ to film thickness of 1.8 ${\mu}{\textrm}{m}$.rm}{m}$.

• 한국초전도ㆍ저온공학회논문지
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• 제11권4호
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• pp.16-19
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• 2009

The influence of nanorods grown on substrate prior to YBCO deposition has been investigated. We studied the microstructures and characteristic of $YBa_2Cu_3O_{7-\delta}$ films fabricated on $SrTiO_3$ (100) substrates with ZnO nanorods as one of the possible pinning centers. The growth density of ZnO nanorods was modulated through Au nanoparticles synthesized on top of the STO(100) substrates with self assembled monolayer. The density of Au nanoparticles is approximately $240{\sim}260\;{\mu}m^{-2}$ with diameters of 41~49 nm. ZnO nanorods were grown on Au nanoparticles by hot-walled PLD with Au nanoparticles. Typical size of ZnO nanorod was around 179 nm in diameter and $2{\sim}6\;{\mu}m$ in length respectively. The ZnO nanorods have apparently randomly aligned and exhibit single-crystal nature along (0002) growth direction. Our preliminary results indicate that YBCO film deposited directly on STO substrate shows the c-axis orientation while YBCO films with ZnO nanorods exhibit any mixed phases without any typical crystal orientation.

• Progress in Superconductivity
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• 제9권2호
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• pp.188-192
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• 2008

We investigated the size effect on quench development in $Au/YBa_2Cu_3O_7$ (YBCO) thin film meander lines on sapphire substrates. The meander lines were fabricated by patterning YBCO films coated with gold layers. The lines were subjected to simulated AC fault current, and immersed in liquid nitrogen during the experiment. After the initial rapid rise, the resistance increased moderately and then slowly. In 4 inch-diameter meander lines, the period during which the resistance increased moderately was considerably longer than in 2 inch-diameter line. Moderate increase of resistance was originated from quench propagation. The film temperature was about 180 K at the point when the propagation was completed. The rate of resistance increase after the quench completion was not affected by the film size.