February 2016
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33 Reads
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February 2016
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33 Reads
December 2014
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95 Reads
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3 Citations
We studied quench propagation in double-sided samples of YBCO thin films covered by a gold top layer and deposited on sapphire wafers. The length of the YBCO structures was up to 0.5 m. A critical current density ~2-3 MA per centimeter square at 77.8 K was found over the entire YBCO film. Quench development in large-area YBCO thin film appears to be a complicated process. Depending on test conditions and external circuit parameters, normal spots may appear and disappear during the quench process. In double-sided samples quench development is strongly affected by thermal interaction between the two films through the substrate’s heat conductivity. This thermal conduction should be considered during the design of fault current limiters made from such films. Mutual thermal interaction of films through a substrate may also be used for acceleration of normal zone propagation using active or passive heaters on opposite sides of the substrate.
July 1999
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40 Reads
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13 Citations
IEEE Transactions on Applied Superconductivity
We studied quench propagation in double-sided samples of YBCO thin films covered by a gold top layer and deposited on sapphire wafers. The length of the YBCO structures was up to 0.5 m. A critical current density ~2-3 MA per centimeter square at 77.8 K was found over the entire YBCO film. Quench development in large-area YBCO thin film appears to be a complicated process. Depending on test conditions and external circuit parameters, normal spots may appear and disappear during the quench process. In double-sided samples quench development is strongly affected by thermal interaction between the two films through the substrate's heat conductivity. This thermal conduction should be considered during the design of fault current limiters made from such films. Mutual thermal interaction of a film through a substrate may also be used for acceleration of normal zone propagation using active or passive heaters on opposite sides of the substrate
July 1997
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13 Reads
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15 Citations
IEEE Transactions on Applied Superconductivity
The current limiting properties of textured and epitaxial YBa2Cu307 films with different thickness on various substrates (i.e. r-cut sapphire, polycrystalline Al2O3 and Y-stabilized ZrO2) are examined. The correlation between structural, morphological, superconducting properties and the evailution of current and electrical field during dc and ac current pulses are determined. The best results are obtained in epitaxial YBa2Cu3O7 films on large-area CeO2/sapphire with a thin Au-top layer. They are characterized by Tc(ind)=88-90K, ΔTc(ind)=O.5K, Jc(77K,res.)=2-3.7MA/cm2 and FWHM(005) = 0.2°. During voltage pulse measurements the highest values for the dissipated power Pmax/A=2.6MW/m2, voltage Umax/l= 10.9 V/cm, and Rmax/Ro=2.33 and the highest mean temperature of the film of Tmax=650-700K could be obtained. The maximum current of (2-6)Ic was reached after ∼4μsec and within lmsec the current was reduced to values below Ic</sub. both being an indicatiion for the fast reaction time and homogeneity of the films. The best values for YBa<sub>2Cu3O7 on polycrystalline Al2O3 and YSZ are Tc,off(ind)=87K, ΔTc=2K, Jc(77K)= 0.2MA/cm<sup>2</sub> and FWHM(005)=0.9° yielding Pmax/A=O.7MW/m2, Umax/l=6.5 V/cm, Rmax/Ro=1.4 (Tmax≈500K) and reaction times of ∼10msec.
January 1997
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9 Reads
Large-area YBa(2)Cu(3)O(7) (YBCO)-films up to 4" are grown on CeO(2) buffered sapphire substrates using an unipolar pulsed (201 kHz) de magnetron sputter process on a 6" magnetron cathode. At optimized deposition parameters, epitaxial c-axes oriented films (FWHM of rocking curve: Delta omega(005) = 0.2 degrees) of high quality are reproducibly obtained. Structure and orientation are determined by x-ray investigations. Inductive and resistive measurements exhibit transition temperatures T(c) > 86 K with Delta T(c) < 0.5 K and critical current densities J(c) > 2.10(6) A/cm(2) at LN(2). The pulsed de sputtering technique offers the possibility of a YBCO deposition on an industrial scale. The advantages and differences with respect to the standard de sputter technique are demonstrated.
June 1995
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7 Reads
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5 Citations
IEEE Transactions on Applied Superconductivity
Superconducting flux-flow transistors were fabricated from thin (50 nm) high temperature superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ films. In order to determine whether the suppression of the critical current by an applied control current is caused by the magnetic induction or thermal heating due to dissipation in the control line, two different device geometries were developed. The first structure consists of a parallel array of short nanobridges and one parallel control line. In the second structure, a single 10 /spl mu/m long nanobridge is arranged with two parallel long control lines placed on both sides of the signal line. Our measurements demonstrate that in both geometries the magnetic induction of the control lines suppresses the transport properties of the nanobridges. However, for control currents larger than the critical current the transport properties of the bridge are additionally strongly suppressed by thermal effects, which are caused by heating of the current-biased control lines. Furthermore, transistor structures with one long nanobridge and two control lines react more sensitively to small control currents than the device with a single and short control line. They can operate at currents far below the critical current, which leads testable transistor devices.
January 1995
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3 Reads
The current limiting properties of large area epitaxial c-axis oriented YBa2Cu3O7 films on sapphire with critical current densities J(c)>2MA/cm(2) are examined. Measurements of the evolution of current, electrical field, power and resistance in time demonstrate the capability of bare and Au-shunted YBCO strip lines to restrict the current within less than 0.5 msec to values below J(c) if exposed to dc and ac excess voltages. However, only up to 5% of the normal state resistance is acchieved in the YBCO layer. The thin film demonstrators are stable even for pulses up to several kW and voltages above 100V. An upscaling up to similar to 90kW seems to be possible with the described technology.
December 1994
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4 Reads
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1 Citation
Physica C Superconductivity
Magnetic hysteresis loops measured with various field sweep rates (sometimes called the dynamic relaxation - DR) enables to extend the lime scale of observable relaxation of induced magnetic moment M to subsecond region even in high magnetic fields and to study fast relaxation processes in vortex system. Relaxation and DR data measured on YBa2Cu3O7 thin flint cover the range of relaxation times 10(-2)-10(4) s corresponding to the range of relaxation rates dj(s)/dt over more than 6 orders of magnitude.
December 1994
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2 Reads
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23 Citations
Superconducting quantum interference devices (dc SQUIDs) were fabricated from high‐temperature superconducting YBa 2 Cu 3 O 7 thin films, using nanobridges as weak links. The weak link behavior in these devices caused by coherent motion of vortices was observed for bridges with dimensions smaller than the effective penetration depth, which was approximately 400–600 nm for the films. The dc SQUIDs consisted of two parallel nanobridges with widths of 100–500 nm. The size of the SQUID hole ranged from 2×2 to 2×10 μm2. The SQUIDs were operated in the temperature range from liquid helium up to 85 K and showed voltage modulations as a function of an applied magnetic field. At 75 K peak‐to‐peak values of 15 μV were observed. The flux noise at 4.2 K was determined to be smaller than 8×10-5 ϕ 0 /√Hz. © 1994 American Institute of Physics.
December 1994
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3 Reads
Physica C Superconductivity
Decay of induced superconducting currents in YBa2Cu3O7 thin films deposited on the CaNdAlO4 substrates was measured by a vibrating sample magnetometer in magnetic fields up to ±2 T and temperatures down to 4.2K. The experimental temperature dependence of the induced current density js is interpreted in terms of the interpolation formula combining effects of thermally assisted flux creep and macroscopic quantum creep. The analysis indicates importance of the macroscopic quantum tunnelling at temperatures bellow ≈ 5K. Significant difference in the js(T) dependences obtained on thin films prepared by different techniques (dc-magnetron sputtering and laser ablation) was observed especially at temperatures T < 0.5 Tc.
... Las curvas E-J de nuestras muestras son análogas a las que en la bibliografía presentan muestras similares. Ver, por ejemplo, las referencias [18,52,53]. Como ya mencionamos en la sec. ...
January 1991
Journal of Applied Physics
... In 1994, Schneider et al. reported on the first nanobridge-based dc SQUID patterned from YBCO thin films [26]. These devices exhibited voltage modulations as a function of the external magnetic field up to 85 K. ...
December 1994
... In our case, this is due to the peculiarities of the motion of the Abrikosov vortices, which enter the nano-bridge when the critical current is reached. When a microwave excitation is added, the nano-bridges display, similarly to Josephson junctions, the Shapiro steps effect in DC-voltage versus current V(I) characteristics; both integer and fractional voltage plateaus are observed [4][5][6][7][8] . To gain microscopic insight into the physical origin of the observed phenomena, we provide time-dependent Ginzburg-Landau (TDGL) calculations in a superconducting nano-bridge in which only a few typical vortex pinning centers-grain boundaries-are present 9 . ...
November 1993
... Promising results for resistive FCLs have been obtained by using HTS thin films deposited on substrates with high heat conductivity and covered by a thin normal conducting layer [3], [6], [47]. Some papers [48] reported that such structures would prevent domains and provide fast propagation of the normal zone. ...
July 1999
IEEE Transactions on Applied Superconductivity
... It can interact with proximate material through either strain or piezoelectric field, resulting in its attenuation or velocity shift 24,25 . Early SAW studies on superconductors mainly focus near the critical temperatures, when the large number of thermally excited quasiparticles can generate a detectable signal if stimulated by SAW 26,27 . However, the large SAW excitation power and thermal fluctuation agitate the vortex and thus cloud the intrinsic vortex dynamics. ...
October 1993
Physical review. B, Condensed matter