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1

Digitale Medien

Transport properties of Tl2Ba2CaCu2O8 weak links on LaAlO3 bicrystal substrates (1996)

Chen, Y. F. ; Ivanov, Z. G. ; Stepantsov, E. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 9221-9223

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated in ex situ epitaxial Tl2Ba2CaCu2O8 films on bicrystal LaAlO3 substrates with symmetric 32° [001] tilt grain boundaries. The critical temperature Tc, of the junctions was in the range 105–107 K and the critical current densities at 77 K varied between 3×102 and 3×104 A/cm2, two or three orders of magnitude less than those of the film. The I–V curves are described by a resistively shunted junction model. Close to Tc, the temperature dependence of the critical current was described by (1−T/Tc)2. The flux noise spectra SΦ(f) of dc SQUIDs were measured in the locked-loop regime with constant current bias at temperatures up to 94 K. The white noise level was 50μΦ0/(square root of)Hz at 77 K. The crossover frequency to 1/f noise was low, about 5 Hz, and the flux noise level at 1 Hz was 440μΦ0/(square root of)Hz. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.362595

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2

Digitale Medien

Microwave testing of high-Tc based direct current to a single flux quantum converter (1994)

Kaplunenko, V. K. ; Fischer, G. M. ; Ivanov, Z. G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 5996-6000

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Design, simulation, and experimental investigations of a direct current to a single flux quantum converter loaded with a Josephson transmission line and driven by an external 70 GHz microwave oscillator are reported. The test circuit includes nine YBaCuO Josephson junctions aligned on the grain boundary of a 0°–32° asymmetric Y-ZrO2 bicrystal substrate. The performance of such converters is important for the development of the fast Josephson samplers required for testing of high-Tc rapid single flux quantum circuits in high-speed digital superconducting electronics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358383

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3

Digitale Medien

Epitaxial YBa2Cu3O7−δ /BaxSr1−xTiO3 heterostructures on silicon-on-sapphire for tunable microwave components (1995)

Boikov, Yu. A. ; Ivanov, Z. G. ; Kiselev, A. N. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 78 (1995), S. 4591-4595

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Epitaxial trilayer heterostructures of YBa2Cu3O7−δ/BaxSr1−xTiO3/YBa2Cu3O7−δ were grown on silicon-on-sapphire buffered by a double layer of CeO2/Y–ZrO2. Such structures may be considered for tunable microwave filters. The top and bottom YBa2Cu3O7−δ films were well c-axis oriented, free from microcracks and had superconducting transitions Tc's in the range 86–90 K. A thin antidiffusion layer of SrTiO3 (d≈70 A(ring)) between YBa2Cu3O7−δ and BaxSr1−xTiO3 (x=0.25–0.9) promoted better crystallinity and higher Tc of the top superconducting film. An Ag/BaxSr1−xTiO3/YBa2Cu3O7−δ capacitor structure was used to determine the dielectric permittivity and the high frequency loss tan δ of the BaxSr1−xTiO3 layer. Maximum values of the permittivity of the BaxSr1−xTiO3 layers were observed around the Curie temperatures of corresponding bulk monocrystals. The dielectric permittivity of the BaxSr1−xTiO3 (x=0.25–0.75) layers depended strongly (≈20%) on an applied voltage (±2.5 V) at temperatures around 77 K. The tan δ was much higher in films than in bulk crystals. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.359804

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4

Digitale Medien

Biepitaxial Josephson junctions with high critical current density based on YBa2Cu3O7−δ films on silicon on sapphire (1995)

Boikov, Yu. A. ; Ivanov, Z. G. ; Vasiliev, A. L. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 77 (1995), S. 1654-1657

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: High-current-density Josephson junctions have been produced in high-temperature superconducting YBa2Cu3O7−δ films deposited on silicon on sapphire and using biepitaxial grain boundaries. The technique is estimated to be useful in integrating superconducting and semiconducting components. A multilayer system of epitaxially grown films was used to form the junctions. A double buffer layer CeO2/ZrO2(9.5% Y2O3) prevented interactions between YBa2Cu3O7−δ and Si during the high-temperature deposition and promoted formation microcrack-free films with a critical current density of 2×106 A/cm2 at 77 K. A MgO seed layer, with (001)MgO(parallel)(001)CeO2 orientation, was used to induce a 45° crystallographic grain boundary in YBa2Cu3O7−δ at its edge. An additional epitaxial buffer double layer of YBa2Cu3O7−δ and SrTiO3 on top of the seed layer promoted the formation of a grain boundary of better crystallinity and stoichiometry. It improved the critical current of the junction about tenfold and resulted in characteristic IcRn products of 150 μV at 77 K in microbridges crossing the grain boundary. Microwave-induced steps were detected at 77 K up to voltages corresponding to the characteristic IcRn value. Peak-to-peak responses to superconducting quantum interference devices reached values of 7 μV at 77 K. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358922

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5

Digitale Medien

Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films (1994)

Nilsson, P. A(ring). ; Ivanov, Z. G. ; Olsson, H. K. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 75 (1994), S. 7972-7977

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y-ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current-voltage curves from junctions with θ(approximately-greater-than)22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer-like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/(square root of)Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC was examined and found to be in agreement with theory [K. Enpuku, Y. Shimomura, and T. Kisu, J. Appl. Phys. 73, 7929 (1993)].

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.356559

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6

Digitale Medien

YBa2Cu3O7−x films on yttria-stabilized ZrO2 substrates: Influence of the substrate morphology (1994)

Brorsson, G. ; Olsson, E. ; Ivanov, Z. G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 75 (1994), S. 7958-7965

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110]YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770 °C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100]YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tconset of 88 K, a ΔT(90%–10%)c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.356557

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7

Digitale Medien

Growth and properties of a multilayer system based on Y1Ba2Cu3Ox and amorphous Y-ZrO2 (1992)

Boikov, Yu. ; Ivanov, Z. G. ; Olsson, E. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 199-202

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The growth of c-axis oriented Y1Ba2Cu3Ox thin films on an amorphous buffer layer of Y-ZrO2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu3Ox and the thickness of the buffer layer. A Tc of 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Ox and amorphous Y-ZrO2 was grown and a Tc of 87 K for the upper c-axis oriented layer was measured.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.352157

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8

Digitale Medien

Epitaxial heterostructures YBa2Cu3O7−δ/KTaO3 for microwave applications (1995)

Boikov, Yu. A. ; Ivanov, Z. G. ; Vasiliev, A. L. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 2708-2710

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Combinations of high TC superconducting and ferroelectric films may give rise to tunable, high-Q microwave components. c-axis oriented YBa2Cu3O7−δ films were grown by laser ablation on (001) and vicinically cut KTaO3 substrates and studied by x-ray diffraction and electron microscopy. Competitive superconducting properties were registered. YBa2Cu3O7−δ/KTaO3/YBa2Cu3O7−δ trilayers were deposited on silicon-on-sapphire buffered by CeO2/Y-ZrO2. The dielectric permittivity of KTO3 at 15–100 K decreased considerably when the layer was polarized by a dc voltage. A loss factor tan δ=0.007 was measured at 100 kHz and T=50–100 K. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.114300

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9

Digitale Medien

Voltage divider based on submicron slits in a high Tc superconducting film and two bicrystal grain boundaries (1995)

Kaplunenko, V. K. ; Ivanov, Z. G. ; Stepantsov, E. A. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 282-284

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Experiments on a model of rapid single flux quantum (RSFQ) flip-flop cell, based on high-Tc (HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y–ZrO2 bicrystals with two asymmetric 32° grain boundaries, about 10 μm apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances ((approximately-equal-to)10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 μm and for ten junctions located close to the tested circuits, the linear critical current densities at T=4.4 K were 10.7 μA/μm±50% for one grain boundary and 8.3 μA/μm±50% for the other one. IcRn was about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip–flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV at T=4.4 K and to 0.4 mV at 30 K. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.114783

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10

Digitale Medien

YBa2Cu3O7/NdGaO3/YBa2Cu3O7 trilayers by modified off-axis sputtering (1993)

Wang, S. Z. ; Olsson, E. ; Alarco, J. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 73 (1993), S. 7543-7548

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: High-quality epitaxial YBa2Cu3O7−δ (YBCO) thin films were achieved by a modified off-axis sputtering technique with high deposition rates (3.3 nm/min). The film quality and the deposition rate depended crucially on the target-to-substrate separation. Epitaxial YBCO/NdGaO3(NGO)/YBCO trilayers were successfully grown onto SrTiO3, Y-ZrO2, and LaAlO3 substrates by dc and rf sputtering. The epitaxial relations were found to be [001]YBCO//[001]NGO, [100]YBCO, or [010]YBCO//[110]NGO and [001]YBCO//[110]NGO, [100]YBCO, or [010]YBCO//[001]NGO, where the latter orientation relationship was dominating. Subsequent top YBCO layers grew c axis oriented independently of the two epitaxial orientations of the NGO. The orientation relationships between YBCO and NGO were the same. Auger electron depth profiles and transmission electron microscopy indicated that the interdiffusion at the interface between the YBCO and NGO layers was not strong even at 740 °C. The superconducting transition temperatures of the top and bottom YBCO layers were about the same as that of YBCO single layers, i.e., 87–90 K. Scanning electron microscopy of the surface morphologies of the YBCO and the NGO showed that a smaller substrate-target distance resulted in smoother films.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.354002

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