• Progress in Superconductivity and Cryogenics
• /
• v.23 no.2
• /
• pp.1-5
• /
• 2021

We have investigated the electrical transport properties of polycrystalline tantalum nitride (TaN_x) films. Various compositions of tantalum (nitride) thin films have been deposited on SiO₂ substrates by reactive DC magnetron sputtering while changing the ratio of nitrogen partial pressure. The substrate temperature was maintained at 283 K during deposition. X-ray diffraction analyses indicated the presence of α-Ta and β-Ta phases in the Ta film deposited in pure argon atmosphere, while fcc-TaN_x phases appeared in the sputtering gas mixture of argon and nitrogen. The N/Ta atomic ratio in the film increased ranging from 0.36 to 1.07 for nitrogen partial pressure from 7 to 20.7%. The superconducting transition temperatures of the TaN_x thin films were measured to be greater than 3.86 K with a maximum of 5.34 K. The electrical resistivity of TaN_x thin film was in the range of 177-577 𝜇Ωcm and increased with an increase in nitrogen content. The upper critical filed at zero temperature for a TaN_0.87 thin film was estimated to exceed 11.3 T, while it showed the lowest T_c = 3.86 K among the measured superconducting TaN_x thin films. We try to explain the behavior of the increase of the residual resistivity and the upper critical field for TaN_x thin films with the nitrogen content by using the combined role of the intergrain Coulomb effect and disorder effect by grain boundaries.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2003.05a
• /
• pp.366-369
• /
• 2003

High T$_{c}$ superconducting lines will be applied as key materials in the areas of power transmission line; magnetic levitation of vehicle; magnetic separation; magnetic energy storage and marine propulsion. A combination method of electrophoresis deposition and zone-melting for preparation of YBaCuO tape is proposed. The submicron particle powder of YBaCuO made by sol-gel method is used in the electrophoresis process. A 40~50${\mu}{\textrm}{m}$ thickness of YBaCuO film on Ag plate could be deposited in about three minutes. After deposition the film is rolled and heat treated in order to increase the density and the adhesion of the film to the Ag plate. Silver(Ag) and lead oxide(PbO) were added in the YBaCuO powder in order to reduce its melting point. The YBaCuO coating with controlled Ag and PbO contents was preliminarily zone-melted at about 945$^{\circ}C$.>.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.11
• /
• pp.997-1002
• /
• 2002

BSCCO thin films are fabricated by an ion beam sputtering method, and sticking coefficients of the respective elements are evaluated. The sticking coefficient of Bi element in BSCCO film formation was observed to show a unique temperature dependence; it was almost a constant value of 0.49 below about 730$^{\circ}C$ and decreased linearly over about 730$^{\circ}C$ In contrast, Sr and Ca, displayed no such remarkable temperature dependence. This behavior of the sticking coefficient was explained consistently on the basis of the evaporation and sublimation processes of Bi$\sub$2/O$\sub$3/. It was concluded that Bi(2212) thin film constructs from the partial melted Bi(2201) phase with the aid of the liquid phase of Bi$\sub$2/O$\sub$3/.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.85-88
• /
• 1999

We fabricated resistive superconducting fault current lmiters based on YBa$_2$Cu$_3$O$_{7}$ thin films and investigated their quench propagation characteristics. The YBa$_2$Cu$_3$O$_{7}$ film was coated with a gold layer and patterned into 1 mm wide meander lines by photolithography. The limiters were tested with simulated fault currents of various fault angles and amplitudes. The quench propagation characteristics were explained based on the heat transfer within the film as well as between the film and the surrounding liquid nitrogen. The quench completion time strongly depended on the potential fault current. It was 1 msec at the peak fault current of 76 A/peak/ and corresponding quench propagation speed was 43 m/sec (film cross section: 4 x 10$^{-6}$ $\textrm{cm}^2$).

• Progress in Superconductivity
• /
• v.4 no.2
• /
• pp.99-103
• /
• 2003

We studied the nonequilibrium superconductivity due to tunnel injection of polaronic quasiparticle (QP) from organic photoconductor. The transport properties of an organic copper (II) phthalocyanine (Cu -Pc)/d-wave superconductor were investigated in dark and under ultraviolet (UV) radiation for performance of a novel $high -T_{c}$ superconducting three terminal device. We observed that the injection of polaronic QP from the organic Cu -Pc film into the $Bi_2$S $r_2$$CaCuO_{8+{\delta}}$ film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. We could increase the current gain by UV excitation of the organic photoconductor injector. The tunneling spectroscopy of a Cu -Pc/BSCCO junction exhibited a small enhancement of the zero bias conductance peak under the W excitation. The above phenomena are of importance in developing optically controlled three terminal superconducting device.e.

• Proceedings of the KIEE Conference
• /
• 1992.07b
• /
• pp.717-720
• /
• 1992

Since the discovery of High-Tc superconducting Y-Ba-Cu-O ceramics with critical temperature of about 90K, numerous efforts to prepare supercond ucting thin films with excellent qualities such as High-Tc and critical current density have been made. The samples were deposited onto $SiO_x$ substrates heated at 540$^{\circ}C$ - 600$^{\circ}C$ in a single target rf - magnetron sputtering system. The film thickness has 2000$\AA$ - 5000 $\AA$ with a rate of 16 $\AA$/min. and distance between target and substrate was 50 mm. The films were characterized by X - ray diffraction, scanning electron microscopy and critical temperature.

• Progress in Superconductivity
• /
• v.5 no.2
• /
• pp.118-123
• /
• 2004

We investigated quench distribution in AU/YBCO thin film meander lines with a heater. Quench distribution during faults is important for superconducting fault current limter applications, because uniform quench allows application of higher voltages across the meander lines. AU/YBCO thin films grown on sapphire substrates were patterned into meander lines by photolithography. Gold films grown on the rear sides of the substrates were also patterned into meander lines, and used as heaters. Meander lines on the front and the rear sides were connected in parallel. The meander lines were subjected to simulated AC fault currents for quench measurements during faults. They were immersed in liquid nitrogen during the experiment for effective cooling. Resistance of the AU/YBCO meander lines initially increased more rapidly with the rear heater than without, and consequently the fault current was limited more. The resistance subsequently became similar, The resistance distribution was more uniform with the heater, especially during the initial quench. Quench was completed more uniformly and significantly earlier. This resulted in uniform distribution of dissipated power. These results could be explained with the concept of quench propagation, which was accelerated by heat transfer across the substrate from the rear heater.

• Progress in Superconductivity and Cryogenics
• /
• v.6 no.2
• /
• pp.7-10
• /
• 2004

A study regarding the epitaxial growth of single $Y_2O_3$ buffer layer on biaxially textured Ni and NiW substrates using pulsed laser deposition is presented. Different deposition conditions were employed and compared in order to obtain good epitaxial $Y_2O_3$ film, furthermore importantly, to obtain good YBCO superconducting films. Following YBCO film deposited by PLD on the top of $Y_2O_3$ films have a good structure and superconducting properties. The J$_{c}$ of YBCO films on $Y_2O_3$ /Ni and $Y_2O_3$ /NiW were $1.0{\times}10^6 A/cm^2 and 1.1\times}10^6 A/cm^2$<.TEX> at 77K and self-field respectively, which indicated that $Y_2O_3$ is a suitable candidate as a single buffer layer for the fabrication of YBCO coated conductor.r.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.11
• /
• pp.1029-1034
• /
• 2003

The Bi$_2$Sr$_2$Ca$_{n}$Cu$_{n+1}$ O$_{x}$, superconducting thin films arc fabricated by using the sputtering and evaporation method. Because we confirmed the sticking ratio of Bi element in the Bi$_2$Sr$_2$Ca$_{n}$Cu$_{n+1}$ O$_{x}$ superconducting thin film fabricated by using the sputtering method was much lower than the expected value, to get the enough number of the flakes of Bi, faraday cup was used to evaporate Bi clement. As a result of the fabrication, Bi 2201 and Bi 2212 single phases could be made by the optima of deposition condition. And we confirmed the sticking coefficient of Bi element was clearly related to the temperature change of the substrate and the generation of Bi22l2 phase

• Journal of the Korean Magnetics Society
• /
• v.20 no.6
• /
• pp.212-215
• /
• 2010

Spin polarized tunneling studies were carried out with Al-Ga bilayer as a spin detector, by Meservey-Tedrow technique. The superconductor (SC)/Insulator (I)/Ferromagnet (FM) tunnel junctions were provided by ultra high vacuum molecular beam epitaxy (UHV-MBE) technique. The analysis of interfacial properties in the Al-Ga bilayer was also carried out by Auger electron spectroscopy. It was observed that the superconducting transition temperature and energy gap were raised in comparison with that of bulk Ga and pure ultrathin Al films. Current studies clearly show how one can modify the material properties at the interface just with a few monolayers.