Thin niobium-silicon multilayers have been sputtered with niobium thicknesses less than the coherence length and silicon thicknesses that allow tunneling between layers. The multilayer structure has been confirmed by X-ray diffraction, and the films have been electrically characterized with respect to T/sub c/ and J/sub c/. For constant Nb thickness, both T/sub c/ and J/sub c/ increase with decreasing Si thickness, indicating increased coupling between the Nb layers. When a multilayer forms the barrier in a tunnel structure, the resulting I(V) characteristic resembles that for a series of single-barrier junctions, and further evidence of Nb interlayer coupling is observed. These multilayers have also been incorporated as the base in several tunnel structures in order to measure the multilayer penetration depth via the magnetic field dependence of I/sub c/. Preliminary results indicate that the theoretically predicted enhancement of penetration depth in a multilayer does occur.<>

Multilayer films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ with composites of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ and LaAlO/sub 3/ have been grown on

YBa/sub 2/Cu/sub 3/O/sub 7/ thin films have been deposited on MgO substrates by off-axis magnetron sputtering in argon, oxygen, and an additional gas. Additions of nitrogen, hydrogen, methane, air, and water vapor in amounts of up to 25% were used in this investigation. Each gas stabilized the target voltage and growth rate for the duration of the deposition. Growth rates improved by over 50% with as little as 3% hydrogen. When used with a target which had degraded after more than 150 h of use, the added gas improved T/sub c/ and J/sub c/ beyond levels attained from the new target. T/sub c/ increased from 82 K without hydrogen to 89 K with hydrogen and J/sub c/ (12 K) from 3*10/sup 4/ to >7*10/sup 6/ A/cm/sup 2/. Nitrogen yielded less dramatic effects. These improvements are attributed to the catalytic effect of these gases in maintaining elevated levels of atomic oxygen during film growth.<>

YBa2Cu307 thin films have been deposited on MgO substrates by off-axis magnetron sputtering in argon, oxygen, and an additional gas. Additions of nitrogen, hydrogen, methane, air, and water vapor in amounts of up to 25% were used in this investigation. Each gas stabilized the target voltage and growth rate for the duration of the deposition. Growth rates improved by over 50% with as little as 3% hydrogen. When used with a target which had degraded after more than 150 hours use, the added gas improved Tc and Jc beyond levels attained from the new target. Tc increased from 82 K without hydrogen to 89 K with hydrogen and Jc(12K) from 3x104 to >7x106 A/cm2. Nitrogen yielded less dramatic effects. We attribute these improvements to the catalytic effect of these gases in maintaining elevated levels of atomic oxygen during film growth.

YBa2Cu3O7−x films have been deposited on MgO by reactive, off-axis magnetron sputtering in an argon, oxygen, and hydrogen gas mixture. The material and electrical properties of the films were studied for deposition temperatures from 600 to 760 °C. The films, all approximately 300 nm thick, were predominantly a-axis oriented when deposited at or below 620 °C but were c-axis oriented when deposited at temperatures above 640 °C. The surfaces of films deposited between 640 and 710 °C were partially covered with a-axis grains. Surface roughness measurements indicated the smoothest films occurred for deposition temperatures below 680 °C. Resistance ratios as great as 3.1 were observed for some films. Transition temperatures exceeded 89 K and resistivities at 100 K were less than 150 μΩ cm for the best films. Low-temperature critical current densities exceeded 107 A/cm2 for films deposited from 640 to 720 °C. The temperature dependence of the critical current density near the transition temperature had a power law dependence of nearly 3/2 for deposition temperatures below 690 °C. The power law dependence decreased for increasing deposition temperatures, dropping to nearly 1.1 in the film deposited at 750 °C.

We have grown thin film composites of and YBa2Cu3O7-x and LaAlO3 by co-sputtering. A film with composition of 10% LaAIO3 by volume had a transition temperature of 58K and critical current density of 1.2 x 106 A/cm2 at 4K. We measured the temperature dependence of the critical current and obtained a good fit with Ginzburg-Landau theory for thin films. A perpendicular magnetic field was applied, and the critical current and pinning force measured. At 70 kOe, the critical current was suppressed only a factor of 4 from its zero-field value. The measured pinning force was 2 x 109 dyn/cm3 at 70 kOe and is comparable to that of YBa2Cu3O7-x films.

Y1Ba2Cu3O7 thin films have been grown on MgO by off-axis magnetron sputtering using mixtures of argon, oxygen, and hydrogen. Reduction in film transition temperature resulting from cumulative target sputtering time (target degradation) is minimized by adding hydrogen to the sputtering gas. Without hydrogen, new targets which had produced films with 87.5 K transition temperatures degraded with deposition time and produced films with transition temperatures of only 82 K. After addition of hydrogen, these targets produced films with transition temperatures of nearly 89 K. Critical-current densities for the films made at optimum hydrogen flow were greater than 3×106 A/cm2 at 4 K. With the addition of hydrogen, we observed a significant increase in the sputtergun cathode voltage and a dramatic increase in the deposition rate. The films were predominantly c-axis oriented, and we observed a minimum c-axis lattice parameter for optimum hydrogen flow. We attribute these improvements in material properties to the catalytic effect of hydrogen in maintaining atomic oxygen in the plasma, allowing more oxygen to be incorporated into the target and the film during growth.

Thin-film composites of co-sputtered Y1Ba2Cu3O7−x and LaAlO3 have been deposited by off-axis magnetron sputtering. Scanning electron microscopy (SEM) and x-ray diffraction studies suggest that LaAlO3 precipitates along the grain boundaries of the Y1Ba2Cu3O7−x grains. The normal state conductivity, transition temperature, and critical current density systematically decreased with increasing LaAlO3 composition, consistent with a decrease in the coupling between Y1Ba2Cu3O7−x grains. Inductive transition widths were only a few degrees wide for all LaAlO3 compositions, indicating homogeneous materials. Initial photoresponse measurements show bolometric behavior near Tc and increased response for greater LaAlO3 compositions.

The photoresponse of Y1Ba2Cu3O7−x step, weak-link devices on MgO substrates has been measured using a He-Ne laser light source. The temperature and magnetic-field dependencies of the device critical current density were investigated. Single-step and multistep devices were fabricated and found to have a bolometric response in the resistive region and weak-link, video-detection response in the superconducting region. These devices are suitable for operation over a wide range of temperatures from 4 to 90 K. Responsivities greater than 1000 V/W were measured at low temperature for some devices.