G. Friedl

Orientation relationships of epitaxial oxide buffer layers on silicon (100) for high‐temperature superconducting YBa2Cu3O7−x films

The preparation parameters of epitaxially grown buffer layers on silicon (100) wafers were investigated. We found that an in situ removal of the native amorphous SiO2 layer from the Si surface is possible, avoiding the etching of the wafer prior to the deposition. YSZ and Y2O3 were chosen as buffer layers for subsequent YBa2Cu3O7−x thin‐film deposition. The orientation of the thin films during the deposition process was analyzed by RHEED. Different orientations on the substrates are obtained depending on the evaporation parameters. TEM studies of the interfaces, x‐ray diffraction analysis, and measurements of the superconducting properties were made after the deposition of the films.

Low 1/f noise single‐layer YBa2Cu3Ox dc SQUID at 77 K

Autonomous single‐layer dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser‐deposited YBa2Cu3Ox films on step edge SrTiO3 and LaAlO3 substrates. For device patterning, a SiOx inhibit technique as well as conventional ethylenediaminetetraacetic wet etch was used. The Josephson junctions are of grain boundary type. Their widths are 5 μm. The SQUID hole is a square of about 5 μm; the SQUID inductance is estimated to be about 20 pH. We obtained a very regular, nonhysteretic flux to voltage modulation over more than 100 flux quanta (Φ0). The maximum voltage signal is of the order of 15 μV peak to peak and the maximum transfer function dV/dΦ at the appropriate flux bias is 50 μV/Φ0 at 77 K. The best value of the equivalent flux noise as measured in the flux locked loop mode is 1.4×10−5 Φ0/Hz1/2 at 1 Hz and 1×10−5 Φ0/Hz1/2 in the white noise region for f≳5 Hz. This results in an energy resolution en,w(f≳5 Hz)=1×10−29 J/Hz in the white noise region and 2×10−29 J/Hz at...

Low 1/ f noise single-layer YBa sub 2 Cu sub 3 O sub x dc SQUID at 77 K

Autonomous single‐layer dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser‐deposited YBa2Cu3Ox films on step edge SrTiO3 and LaAlO3 substrates. For device patterning, a SiOx inhibit technique as well as conventional ethylenediaminetetraacetic wet etch was used. The Josephson junctions are of grain boundary type. Their widths are 5 μm. The SQUID hole is a square of about 5 μm; the SQUID inductance is estimated to be about 20 pH. We obtained a very regular, nonhysteretic flux to voltage modulation over more than 100 flux quanta (Φ0). The maximum voltage signal is of the order of 15 μV peak to peak and the maximum transfer function dV/dΦ at the appropriate flux bias is 50 μV/Φ0 at 77 K. The best value of the equivalent flux noise as measured in the flux locked loop mode is 1.4×10−5 Φ0/Hz1/2 at 1 Hz and 1×10−5 Φ0/Hz1/2 in the white noise region for f≳5 Hz. This results in an energy resolution en,w(f≳5 Hz)=1×10−29 J/Hz in the white noise region and 2×10−29 J/Hz at...

High-resolution electron microscopy of epitaxial YBCO/Y 2 O 3 /YSZ on Si(001)

The microstructures of YBa 2 Cu 3 O 7−δ (YBCO) thin films grown on Si with Y-stabilized ZrO 2 (YSZ) and Y 2 O 3 buffer layers were characterized by means of high-resolution electron microscopy. At the Si–YSZ interface, a 2.5 nm thick layer of regrown amorphous SiO x is present. The layer is interrupted by crystalline regions, typically 5 to 10 nm wide and 10 to 50 nm apart. Close to the crystalline regions, {111} defects are present in the Si substrate. The typical defect observed is an extrinsic stacking fault plus a perfect dislocation close to the stacking fault which terminates extra {111} planes in the upper part of the Si. These defects are probably formed by condensation of Si self-interstitials created during oxide regrowth. Precipitates are present in the Si close to the Si–YSZ interface and indicate that in-diffusion of Zr has occurred. The YSZ–Y 2 O 3 interface is atomically sharp and essentially planar and contains no second phases. Perfect misfit dislocations with Burgers vector 1/2〈110〉 are present at this interface along with unrelaxed elastic misfit stresses. The Y 2 O 3 –YBCO interface is atomically sharp and planar, but contains steps. (001) stacking faults are present in the YBCO above these steps; the faults are, however, healed a few unit cells away from the interface. By HREM analysis of ultrathin specimen areas, the atomic layer of the YBCO closest to the Y 2 O 3 was found to be a barium-oxygen layer.

Transport properties of epitaxial YBa2Cu3Ox films at step edges

To study the current‐carrying capability of interconnections between conducting planes in a YBa2Cu3Ox‐insulator multilayer system, the transport properties of laser‐deposited YBa2Cu3Ox striplines at different step edges in 〈100〉 SrTiO3 substrates were investigated. Step edges with various heights between 100 and 800 nm and slope angles a=2.5°, 10°, 25°, 40°, and 65° were fabricated by Ar+ ion milling. The previous ion milling of one part of the substrate does not affect the crystal growth and the transport properties of the superconductor, which has been checked by electrical and x‐ray measurements. Two ways for a high transport current between conducting planes were realized. At flat angles up to 30°, a critical current density of ≳106 A/cm2 at 77 K can be achieved for a step stripline with film thickness d0 smaller than the step height h. If the film thickness d0 is larger than the step height, high superconducting current densities can also be achieved for a≳65°.

Noise properties of YBaCuO step edge DC-SQUIDs with different inductance

Autonomous step edge DC-SQUIDs (superconducting quantum interference devices) with inductances between 20 pH and 140 pH have been prepared on one chip. The noise properties of these devices have been determined by operating them in the flux locked loop. The best energy sensitivity of 6*10/sup -31/ J/Hz was obtained for a 20 pH SQUID and frequencies above 100 Hz. The frequency-dependent noise for the best devices was about 2*10/sup -29/ J/Hz at 1 Hz and could be reduced by applying an AC bias.<<ETX>>

Transport properties of YBaCuO step edge Josephson junctions

Step edge Josephson junctions have been prepared on

Flux penetration into YBa2Cu3Ox thin films covering substrate step edges

Using the high‐resolution Faraday effect, the flux penetration into YBa2Cu3Ox thin films grown over one or two substrate step edges is directly observed at a temperature of T=5 K. The regions at the steps are easily penetrated by the flux already present at low applied external magnetic fields due to the locally enhanced stray fields. The step edges are found to separate the sample magnetically into independent parts. It is also shown that the local observation of flux penetration allows detection of the influence of defects in the thin‐film samples on the domain structures in a direct way.

Preparation and characterization of planar YBa/sub 2/Cu/sub 3/O/sub x/ flux transformers

Planar magnetometer and gradiometer flux transformers, which can be used for high-temperature superconductor superconducting quantum interference devices (SQUIDs), were fabricated from epitaxial, excimer-laser-deposited YBa/sub 2/Cu/sub 3/O/sub x/ three-layer stacks. The first YBa/sub 2/Cu/sub 3/O/sub x/ layer and the SrTiO/sub 3/ insulator layer were deposited through silicon shadow masks. As the edges of these layers are very smooth, a second YBa/sub 2/Cu/sub 3/O/sub x/ film can grow epitaxially onto the device without forming grain boundaries. It was subsequently patterned by argon ion milling to magnetomer and gradiometer flux transformers with up to 12 turns and 25- mu m linewidth. The flux transformers were characterized by resistance and persistent current measurements, using a conventional SQUID magnetometer. At 77 K a persistent current of about 1 mA was measured in the flux transformer with 50- mu m linewidth.<<ETX>>

Basic elements of high temperature superconductor wiring

Abstract Laser deposited YBa 2 Cu 3 O x multilayers were patterned by means of a new lift-off technique, using a high-temperature-resistant CaO process mask. A crossover contact with a cross-section of 3ωm·3ωm was fabricated with this method, carrying a critical current > 14 mA. YBa 2 Cu 3 O x striplines were deposited across substrate steps to investigate the current carrying capability between conducting planes in an YBa 2 Cu 3 O x -insulator multilayer system.