Search

A study is conducted on a 160-nm-thick (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re0-1212] epitaxial thin films that were fabricated on 2degree-18.4degree -tilt SrTiO3 vicinal substrates with thin buffer layers. The studies indicate that the vicinal films had superior crystallinity and superconducting properties comparable to those for conventional films with no tilt.

The packaging and assembling techniques for the bit error rate (BER) measurement system is examined and the system configuration is improved to obtain a lower measurable limit of BER. This led to a BER less than 10(sup -12) at an output voltage of 1.7 and 2.3 mV for ducting microstrip-line to coplanar-waveguide transmission-line converter.

Interface-engineered ramp-edge Josephson junctions with different critical current values and different electrode materials are investigated by transmission electron microscopy. La doping seems to suppress the formation of Y(sub 2)O(sub 3) and reduce the lattice mismatch between the barrier and the electrodes.

High temperature superconducting rapid single flux quantum circuits were fabricated and tested using interface engineering Josephson junction.

Research is presented describing the study of surface barriers of Josephson junctions which have modified ramp-edges resulting in differing superconductivity levels.

Inductive coupling between Quantum-Flux-Parametron (QPF) gates for signal transfer is proposed in place of the direct coupling method as a means of improving the signal isolation. Inductively coupled gates were used to design and fabricate majority gates, which are the principal logic elements of the QFP circuits. Transient properties of the QFP gates upon application of an activation current were also examined by the numerical simulation.

A proposed measurement method for the critical current (I (sub c)) distribution for the resistively shunted junctions (RSJs) is described. The I(sub c) distribution of the RSJ-type junction is examined by arraying the junctions in series. The factors responsible for the I(sub c) spread, the integration scale and the conditions under which the I(sub c) measurement method can be used are discussed. The proposed method is applicable to any other RSJ-type junctions.

[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]

The properties of (Hg,Re)[Ba.sub.2]Ca[Cu.sub.2][O.sub.y] ((Hg,Re)-1212) [100]-tilt junctions are described for this two types of [100]-tilt junctions, that is, a mountain-type junction and a valley-type junction of which a-b planes formed a mountain shape and a valley shape along the grain boundaries, respectively are compared. The hysteresis behavior is explained by flux penetration between the Cu[O.sub.2] planes that is associated with the large anisotropy of (Hg,Re)-1212.

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.

Abstract: We examined temperature dependence of the I c R n (I c being the critical current and R n being the normal-state resistance) product for interface-engineered YBa2Cu3O7−x ramp-edge junctions formed on a groundplane. There were two types for the temperature dependence of the I c R n product. One was the linear temperature dependence, and the other was a dependence that shows the steeper drop with temperature. There were two factors that were responsible for the temperature dependence of the I c R n value. These were critical temperature T c of the junctions and temperature dependence of the R n value. The I c R n value more than 1mV at 40K was obtained for the junction that had the T c of 84K and the positive coefficient of R n value on temperature. [Copyright &y& Elsevier]

Studies the fabrication of NdBa2Cu3O7 − x interface-modified ramp-edge junctions by metalorganic chemical vapor deposition (MOCVD). Examination of the preparation conditions of 300-nm-thick NBCO films for fabrication of ramp-edge junctions; Fabrication of the NBCO and SAT films separately; Deposition of the high-quality c-axis orientated NBCO films with a thickness of 300 nm.

Quantum Flux Parametron (QFP) logic gates were designed and fabricated from a single layer of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film based on step-edge Josephson junctions. Self-inductance (L) of the QFP loop, an important circuit parameter, as is critical current (J/sub c/) of the Josephson junction, was determined by using directly coupled dc superconducting quantum interference devices (SQUIDs). Magnetically coupled dc SQUIDs were used to detect the output signal from the QFP. Simulated waveforms were used to identify the operation modes of the QFP as a function of the circuit parameters. From examination of the output waveforms of the QFP, operation in agreement with simulations was confirmed. [ABSTRACT FROM PUBLISHER]

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]