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[100]-tilt grain boundary Josephson junctions with misorientation of the c-axis directions have been fabricated using epitaxial (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] thin films grown on SrTiO3 bicrystal substrates. Two types of the [100]-tilt junctions, that is, the mountain-type junction and the valley-type junction, of which a-b planes formed a mountain shape and a valley shape along the grain boundaries, respectively, were examined for various misorientation angles (θ). Both the types of junctions showed resistively shunted junction-type current-voltage (I-V) characteristics with relatively high characteristic voltages in a wide temperature range from 4.2 to 110 K. The valley-type junctions exhibited properties superior to those for the mountain-type junctions, such as very low excess current and much homogeneous current distribution, which is attributed to different film growth mode near the grain boundaries. They also exhibited the products of the critical current (Ic) and the normal-state resistance (Rn) as high as 3.0–4.2, 1.0–1.4, and 0.2–0.4 mV at 4.2, 77, and 100 K, respectively. The misorientation angle dependences of junction parameters for the [100]-tilt junctions were compared with those for conventional [001]-tilt junctions with misorientation of the a-b plane directions. The Rn and the IcRn products for the [100]-tilt junctions were substantially larger than those for the [001]-tilt junctions. Large hysteresis in the magnetic-field dependence of Ic was observed for the applied field larger than a certain threshold value, suggesting flux penetration between the CuO2 planes. [ABSTRACT FROM AUTHOR]

Approximately 160-nm-thick (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] epitaxial thin films were fabricated on 2°–18.4°-tilt SrTiO3 vicinal substrates with thin buffer layers. The vicinal films had superior crystallinity and superconducting properties comparable to those for conventional films with no tilt. X-ray diffraction measurements revealed that the tilt angles of the c axes of the (Hg,Re)-1212 are slightly larger by 0.5°–1.5° than the substrate tilt angles, which is attributed to deformation of crystal structure due to lattice mismatch in the c-axis direction. The resistivity and critical current density along the c-axis direction (ρc and Jc-c) were estimated to be ρc=500 mΩ cm at room temperature and Jc-c=(1.0–1.4)×105 A/cm2 at 10 K from transport measurements for different in-plane directions of the vicinal films. The ρc clearly exhibited semiconductor-like temperature dependence below 180 K. The temperature dependence of Jc-c almost agreed with the theoretical relationship for superconductor-insulator-superconductor junctions. The current–voltage characteristics in the directions across their a–b planes exhibited a multiple branch structure of intrinsic Josephson junctions with voltage jumps at intervals of approximately 20 mV at 4–40 K. [ABSTRACT FROM AUTHOR]

Interface-engineered ramp-edge Josephson junctions with different critical current values and different electrode materials are investigated by transmission electron microscopy. High- resolution transmission electron microscopic observations show the coexistence of Y[SUB2]O[SUB3], Y[SUB2]Ba[SUB2]O[SUB5], and a Ba-based pseudocubic phase in the barrier. The formation mechanism is related to the etching time and the composition of electrode materials. It is found that Y[SUB2]O[SUB3] domains with typical sizes between 4 and 25 nm[SUP2] frequently exist in the thick regions of the barrier and the more the base electrode is fully covered by the domains of these phases, the lower the critical current value; the higher the fraction of Y[SUB2]O[SUB3] and Y[SUB2]Ba[SUB2]O[SUB5] to the Ba-based pseudocubic phase in the barrier, the larger the I[SUBc] spread. Moreover, the atomic structure and the composition of the barrier in the junctions with La-doped electrodes are examined. La doping seems to suppress the formation of Y[SUB2]O[SUB3]and reduce the lattice mismatch between the barrier and the electrodes. In the junction with the highest critical currant value, them are many Y extra planes, i.e., stacking faults rather than cubic or pseudocubic phases along the barrier, therefore, it seems that the barrier is composed of many minute grain boundaries between the 123 and 223 phases. [ABSTRACT FROM AUTHOR]

Presents a study that described the fabrication of a NbN/Nb oxide/NbN Josephson junction and transmission electron microscopy observations of their cross-sectional structure. Correlation of junction characteristics with observed structures; Fabrication process of NbN/Nb oxide/NbN trilayer film; Analysis of the local distribution of tunneling currents within the Josephson junction.

Presents a study to investigate a measurement method for the critical-current distribution of the resistively shunted junction. Methodology used to conduct study; Indication of findings; Discussion on results.

We designed a quasi-one junction superconducting quantum interference device (QOS) based on single-flux-quantum technology using high-Tc superconductors. A circuit containing 10 interface-engineered ramp-edge Josephson junctions was fabricated on a La-substituted YBa2Cu3Oy ground plane. The output voltage as a function of the input current for the QOS indicated correct operation as a periodic comparator at clock frequency of 94 and 77 GHz at 35 and 40 K, respectively. A comparison of the observed maximum operating frequency with the product of the critical current and normal resistance for the junctions suggests that comparator operation above 100 GHz at 40 K is possible if one optimizes the junction parameters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A logic gate has been fabricated with the partial use of high-temperature superconducting films and tested to study digital applications of such films. The logic gate consists of three YBa2Cu3O7-x/Ag/Pb-In superconducting weak links and three inductors. The current-voltage characteristics of the weak links are nonhysteristic. The logic gate successfully provides and and or logic results for two external digital inputs at 4.2 K. [ABSTRACT FROM AUTHOR]

Presents a yttrium-barium-copper-oxygen step-edge direct current superconducting quantum interference device. Presence of coplanar control lines in the device; Utilization of silicon double-mask layers in the construction of the step-edge junctions; Range of the spacing between the closed loop and the coplanar control lines.

A chain circuit of direct coupled logic gates consisting of niobium nitride (NbN)-lead (Pb) alloy electrodes has been fabricated. The junctions used were of 1.5 μm square and had a current density of 20 kA/cm2. A special sampling method with jitter of ±1.5 ps was used to precisely measure the short delay time. A minimum logic delay of 5.6 ps/gate has been obtained with a fan in=fan out=1 structure. [ABSTRACT FROM AUTHOR]