• 한국초전도학회:학술대회논문집
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• v.9
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• pp.124-128
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• 1999

We report microwave properties of high-T$_c$ superconducting (HTS) microstrip antennas without impedance matching circuits, where the impedance mismatching is obvious under the critical temperature (T$_c$). The superconducting thin films used in this report were YBa$_2Cu_3O_{7-x}$ (YBCO) films deposited on MgO substrates produced by pulse laser deposition (PLD) technique. At around T$_c$, 86 K the reflection coefficient rapidly drops, and the standing wave ratio (SWR) becomes almost unity, and the characteristic impedance based on the Smith chart is nearly 50 ${\Omega}$. The reflection coefficient and the SWR of the HTS microstrip antenna were - 62.52 dB and 1.0015, respectively, at the resonant frequency of 11.812 CHz at 86 K.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.75-82
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• 1999

TE$_{01\;{\delta}}$ mode Cavity Resonators with a low loss dielectric rod and YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) endplates were prepared and their microwave properties were studied at temperatures above 30 K. Both sapphire and rutile were used as the dielectrics. The TE$_{01\;{\delta}}$ mode Q$_0$ of the resonator, designed to work as a tunable resonator with variations in the gap distance (s) between the dielectric rod and the top YBCO, was more than 1000000 at s = 0 mm and at 30 K and .the resonant frequency of 19.56GHz when a sapphire rod was used for the dielectric. The TE$_2Cu_3O_{7-{\delta}}$ mode resonant frequency (f$_0$) appeared to decrease as the temperature is raised. Meanwhile, the temperature dependence of the TE$_2Cu_3O_{7-{\delta}}$ mode f$_0$ of the rutile-loaded resonator appeared different with f$_0$ increasing according to the temperature and Q$_0$ more than 300000 at 30 K and f$_0$ = 8.56 CHz. Comparisons were made between the microwave properties of the sapphire-loaded and the rutile-loaded resonators. Also, applications of the TE$_2Cu_3O_{7-{\delta}}$ mode cavity resonator for a tunable resonator with a very high Q$_0$ as · well as a characterization tool for surface resistance measurements of HTS films are described.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.112-115
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• 2000

In this work the results of the systematic investigations on the effect of organic addition by using polymer compound as starting materials on the superconducting properties of YBCO electrophoretic deposited films on silver substrate are presented. The characteristics of the films were examined by X-ray diffraction and SEM observation. Our results show that the adhesion and microstructure of these films are sensitive to the nature of polymer compounds and sintering conditions (electrophoretic deposition, drying and heat-treatment procedures). To develop optimum microstructures for samples processed in this manner it is necessary to have an understanding of how these processes affect the microstructure and hence the properties of ceramic superconductors.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.688-691
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• 1997

Good quality superconducting $YBa_2Cu_30_{7-{\delta}}$(YBCO) thin films were grown on Hastelloy (Ni-Cr-Mo alloys) with yttria-stabilized zirconia(YSZ) buffer layers by in situ pulsed laser deposition in a multi-target processing chamber. Generally, Hastelloy exhibits excellent resistance to corrosion, fatigue, thermal shock, impact, and erosion. However, it is difficult to make films on flexible metallic substrates due to interdiffusion problems between metallic substrates and superconducting overlayers. To overcome this difficulty, it is necessary to use YSZ buffer layer since it will not only limit the interdiffusion process but also minimize the surface microcrack formation due to smaller mismatch between the film and the substrate. In order to enhance the crystallinity of YBCO films on metallic substrates, YSZ buffer layers were grown at various temperatures different from the deposition temperature of YBCO films. On YSZ buffer layer grown at higher temperature than that for depositing YBCO film, the YBCO thin film was found to be textured with c-axis orientation by x-ray diffraction and had a zero-resistance critical temperature of about 85K.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.288-290
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• 1997

Pulsed laser ablation has been used to fabricate superconducting $YBa_2Cu_3O_{7-x}$(YBCO) thin films on MgO substrates. The epitaxial YBCO thin films were grown at $750^{\circ}C$ and oxygen partial pressure of 200 mTorr. The electrical property and the characteristics of the YBCO thin films have been studied by R-T measurement. scanning electron microscopy (SEM) and X-ray diffraction (XRD). A microstrip line resonator has been fabricated using YBCO superconducting thin films by photolithography and wet-etch process. The resonator has linear microstrip line separated by a gap of 0.278 mm. We observed a fundamental resonance peak at the frequency of 10.007 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.112-115
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• 2000

In this work the results of the systematic investigations on the effect of organic addition by using polymer compound as starting materials on the superconducting properties of YBCO electrophoretic deposited films on silver substrate are presented. The characteristics of the films were examined by X-ray diffraction and SEM observation. Our results show that the adhesion and microstructure of these films are sensitive to the nature of polymer compounds and sintering conditions (electrophoretic deposition, drying and heat-treatment procedures). To develop optimum microstructures for samples processed in this manner it is necessary to have an understanding of how these processes affect the microstructure and hence the properties of ceramic superconductors.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1137-1139
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• 1993

The superconducting thin films of $YBa_2Cu_3O_{7-x}$ were deposited on (100) sapphire substrates at low temperature by rf magnetron sputtering and annealed at $895^{\circ}C$ for 60 sec. using rapid-thermal-annealing(RTA) technique. The films were characterized by SEM, four-point probe resistivity measurement, XRD, and AES. The RTA processed HTS films had a preferential structure with c-axis normal to the substrate surface.

• Electrical & Electronic Materials
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• v.6 no.4
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• pp.318-323
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• 1993

본 연구에서는 rf magnetron 스퍼터링으로 (100) 사파이어 기판에 퇴적시킨 YBa$_{2}$Cu$_{3}$$O_{7-x}$박막을 열처리하기 위하여 급속 열처리 방법을 사용하였다. XRD, AES, 그리고 4단자 비저항 측정법을 사용하여 급속 열처리로 형성시킨 초전도체 박막과 기판사이의 상호확산을 조사하였다. 제조된 박막은 91K에서 Tc(onset)를 80K에서 Tc(zero)를 나타내었다. AES 분석 결과, 급속 열처리 방법의 경우 YBa$_{2}$Cu$_{3}$$O_{7-x}$ HTS 박막과 기판사이의 계면에서 항호확산이 감소되는 것을 확인하였다. XRD 분석 결과, 급속 열처리에 의해 형성된 HTS 박막은 주로 c-축이 기판의 표면에 수직인 구조를 가지고 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.250-254
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• 2000

High temperature superconducting films deposited on metal Ag wire were prepared with YBCO powders by electrophoretic deposition method. $I_2$was used as additives for surface charge of YBCO particles. When 2~3 wt.% $BaF_2$ was added in the YBCO suspension, the pores and cracks of film surface were decreased and film density could be increased. In case of YBCO films, the critical current density ($J_{c}$) was calculated at the value of $1458{\;}A/\textrm{cm}^2$ (77K, 0K) by 4 point prove method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.794-797
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• 2000

The fabrication of high quality superconducting thin films using pulsed laser deposition (PLD) has been reported to find optimized processing conditions and to make the millimeter-wave devices. High temperature superconducting (HTS) YBCO films were prepared on MgO (10${\times}$10${\times}$0.5mm) substrates by the PLD. The 3 pole bandpass filter with the center frequency of 22 GHz for satellite communication was designed consisting of hairpin coupled-lines to reduce the configuration in size. YBCO films are c-axis oriented and show superconductive transition temperatures of 88∼89 K with the transition widths < 0.5 K. The insertion loss of passband at 70 K was about 5 dB. The measured frequency response of superconducting filter will be compared with the simulation result.