The deposition conditions of Y0.9Ba1.9La0.2Cu3Oy (La-YBCO) and (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) thin films were studied with the aim of fabricating ramp-edge Josephson junctions on a superconducting ground plane. These films were deposited by a magnetron sputtering method and utilized as a base electrode and an insulating layer under the electrode, respectively. YBa2Cu3Oy thick films grown by liquid phase epitaxy (LPE-YBCO) were used for a ground plane. Insertion of a SrTiO3 buffer layer between LSAT and LPE-YBCO significantly improved the flatness of the film surface. La-YBCO films with a flat surface and Tc (zero) of 87K were reproducibly obtained by DC sputtering. We have fabricated ramp-edge Josephson junctions using these films. Resistively and capacitively shunted junction (RCSJ)-like characteristics were observed in them. An Ic spread of 10.2% (at 4.2K, average Ic = 0.5 mA) was obtained for a 1000-junction series-array.

The high performance method for analyzing the time evolution of the shielding current density in the high Tc superconductor (HTS) has been investigated. After discretized by using the finite element method and the backward Euler method, the initial-boundary-value problem of the governing equations of the shielding current density is transformed to the problem in which the nonlinear algebraic equations are solved at each time step. When the deaccelerated Newton method (DNM) is applied to the solution of the equations, a decrease in the relaxation factor will not always ensure the convergence of iterations. For this reason, the DNM is modified so that the residual norm may decrease monotonously with the iteration number. The modified method is called the adaptively deaccelerated Newton method (ADNM). Although the vector function is evaluated several times at each cycle in the ADNM, the CPU time required for the ADNM is diminished considerably as compared with that for the DNM. This result indicates that the ADNM is suitable for calculating the shielding current density. The numerical code for analyzing the shielding current density has been developed on the basis of the ADNM and, as an application of the code, the magnetic shielding performance of an axisymmetric HTS plate has been analyzed.

This paper reports the design and fabrication of a miniaturized superconducting microstrip line filter using YBCO film on MgO. The filter's resonators are shaped in a double spiral, and the size of the resonators is optimized from the standpoint of the unloaded Q-factor. The 15-pole bandpass filter that has the center frequency of 1.95 GHz and the bandwidth of 20 MHz is designed in the size of 9.7 44 mm. The simulated S-parameter characteristics of the filter is corresponding to the initial design parameters. We fabricated the filter on an MgO substrate with a diameter of 2 inches. The filter had very sharp cutoff and a very low insertion loss of 0.14 dB.

The frequency dependence of surface resistance Rs of high temperature superconductor (HTS) films are measured by a novel measurement method using four TE0mp modes in a sapphire rod resonator. At first, a loss tangent tan δ of the sapphire rod and Rs of the HTS films are evaluated separately from the results measured for the TE021 and TE012 modes with close resonant frequencies. Secondly, Rs values at two different resonant frequencies for the TE011 and TE022 modes are measured using a well-known relation for sapphire tan δ/f = constant, where f is a frequency. Rs values of HoBa2Cu3O7-x thin films were measured in the frequency range of 10 to 43 GHz by using four sapphire rod resonators with different sizes. As a result, it is found that these measured results of Rs have a characteristic of frequency square.

We have developed a 2 GHz band superconducting 8-pole tunable quasi-elliptic function filter on sapphire substrate. The tunable filter has a sharp skirt characteristic by transmission zeros. And the tunable filter uses a low-cost substrate of sapphire. An adjustment of center frequency for the filter is realized by a tunable technique with a piezoelectric bending actuator. The tunable filter realized center frequency shift of 7.62 MHz with conditions of bandwidth change of 0.5% and ripple change of 0.25 dB. Center frequency of the 8-pole quasi-elliptic function filter agreed with the designed value. Given these features, a superconducting filter with a sharp skirt characteristic for next-generation mobile RF applications is expected to be realized by applying these filters.

A compact high-temperature superconducting (HTS) bandpass filter (BPF) using coplanar waveguide (CPW) meander-line parallel-circuited resonators is proposed for microwave receiver applications. The design theory is presented based on a conventional filter theory with J-inverters. Also, analytical and numerical studies of the meander-line resonator are carried out in terms of equivalent circuit values, the resonant frequency, and the unloaded Q. Two- and four-stage 0.05 dB ripple Chebyshev BPFs at 2 GHz with relative bandwidth 60 MHz are fabricated with the metalorganic deposition (MOD)-derived YBCO films on LaAlO3 substrates and their performance are demonstrated. The measured frequency characteristics and the unloaded quality factors agree well with the theoretical and numerical results and the validity of the design theory is confirmed.

A high temperature superconductor (HTS) 5 GHz 10-pole bandpass filter (BPF) is designed by using coplanar waveguide (CPW) quarter-wavelength resonators. The 10-pole Chebyshev BPF has a center frequency 5.0 GHz and a fractional bandwidth 3.2%. Based on an equivalent circuit with J- and K-inverters, the filter is first designed by using an EM simulator. Next an optimization algorithm is employed to diagnose the discrepancy between the filter responses calculated by the EM simulator and the equivalent circuit. Adjustment of the dimensions of the filter is made thereby. The frequency response of the adjusted filter satisfies well the design specifications.

A new measurement method using two resonance modes, the TE021 and TE012 modes, in an image-type dielectric resonator is proposed to measure the surface resistance Rs of only one high-Tc superconductor (HTS) film and the loss tangent tan δ of a sapphire rod separately, precisely and nondestructively. The image-type resonator is constructed by placing a sapphire rod in a bottom of a conductor cavity made of two HTS films and a copper ring. This resonator is designed from the mode charts calculated on the basis of the rigorous analysis by the mode matching method, taking account of an uniaxial-anisotropic characteristic of sapphire. It is verified that the mode charts are also effective to identify many resonance modes observed in measurement. The temperature dependence of Rs of one YBCO film was measured at 19.3 GHz by this method. The measured result agreed very well with one measured by the conventional two-dielectric resonator method. As a result, it was verified that this method is useful to evaluate Rs value of one HTS film with no damage.

Lymph-node detection system using a high Tc SQUID and ultra-small particles was proposed. Pseudo lymph nodes containing small iron particles were made and the magnetic signal was measured. The SQUID signal was proportional to the weight of the iron in the fluid. At the distance of 20 mm, the detectable minimum weight of the iron was 40 µg. We demonstrated that the possibility of the application of the system to the human body.

We describe here development of a multichannel high-Tc SQUID magnetometer system for measurement of cardiac magnetic fields, aiming at future application of diagnosis of heart diseases. Two types of direct-coupled SQUID magnetometers were fabricated and used: single pickup coil magnetometer having flux dams to suppress the shielding current that would induce flux penetration and the consequent low-frequency noise, and double pickup coil magnetometer having no grain boundary junctions and flux dams on the pickup coil. The superconducting film of both the magnetometers had holes and slots, leaving 5 µm-wide strip lines, to suppress trapping and penetration of magnetic flux vortices in environmental fields. We studied different schemes of active shielding to reinforce the efficiency of field-attenuation of magnetically shielded room (MSR). A feedback-type compensation using a normal detection coil wound around the wall of MSR and a selective cancellation of 50 Hz noise by means of adaptive filter were developed. Such combination of passive and active shielding, based on the use of simple MSR, would be suitable in a practical low-cost magnetometer system for clinical MCG examination. We fabricated a liquid nitrogen cryostat that could contain up to 20 magnetometer-capsules at 4 cm separation in a flat bottom, with a distance of 16 mm between the air and liquid nitrogen. The cryostat was set in a gantry, which had rotational, vertical and horizontal freedoms of movement, in a moderate-shielding MSR that was combined with the developed active shielding. Measurements of MCG were performed for normal subject using eight magnetometers operating simultaneously.

A new structure of a low-loss high temperature superconducting (HTS) filter is proposed by using quarter-wavelength coplanar waveguide (CPW) resonators. A 4-pole Chebyshev band-pass filter with the center frequency 5.0 GHz and the 0.01 dB-ripple fractional bandwidth 3.2% is designed based on the theory of direct-coupled resonator filters using K- and J-inverters. This filter is fabricated by using a high-Tc superconductive YBCO film deposited on a MgO dielectric substrate. The frequency response of the filter measured at 60 K agrees very well with the theoretical one. The insertion loss is 0.22 dB. The insertion loss of this filter is the lowest in HTS-CPW filters presented so far.

We fabricated ramp-edge junctions with barriers by modifying surface and integrating ground-planes. The fabricated junctions had current-voltage characteristics consistent with the resistive shunted-junction model. We also obtained a 1-sigma spread in the critical current of 7.9% for 100 junctions at 4.2 K. The ground-plane reduced the sheet inductance of a stripline by a factor of 3. The quality of the ground-plane was improved by using an anneal in oxygen atmosphere after fabrication. The sheet inductance of a counter-electrode with a ground-plane was 1.0 pH per square at 4.2 K.

We report recent achievements in interfacing Josephson junction circuits with superconductor MicroStrip Lines (MSLs). We studied basic techniques that allow satisfactory operation of different devices with MSLs. Successful operation of the interfaces with very low error rate has been demonstrated even at the MSL resonant frequency.

A coaxial cable measurement system applicable up to 60 GHz in the cryogenic temperature is developed by using V-connectors. In this system, the fine location of coupling loop antennas can be adjusted by three-dimensional mechanical stages in the low temperature region. In order to verify usefulness of this system, the temperature dependence of surface resistance (Rs) of Y-Ba-Cu-O (YBCO) films was measured at 30 GHz by the two-dielectric resonator method using TE011- and TE013- mode sapphire rod resonators. The measured result of Rs was 0.5 mΩ at 30 GHz and 20 K, which was 1/40, compared with those of copper plates.

We report the measurements on the ramp-edge type Josephson and quasiparticle tunnel junctions with the different interface angle geometry using high-Tc YBa2Cu3O7-y (YBCO) electrodes. The YBCO/I/Ag tunnel junctions with different crystal-interface boundary angles are fabricated for the investigation of zero bias conductance peak. The angle dependent zero bias conductance peak typical to a dx2-y2-wave superconductor is observable. For Josephson junctions, YBCO ramp-edge junctions with different ab-plane electrodes relatively rotated by 45are fabricated using a CeO2 seed-layer technique. The temperature dependence of the maximum Josephson current for YBCO/PBCO/YBCO junctions (PBCO: PrBa2Cu3O7-y) exhibits angle-dependent behavior, qualitatively different from the Ambegaokar-Baratoff prediction. Under microwave irradiation of 9 GHz, the Shapiro steps appear at integer and/or half integer multiples of the voltage satisfying Josephson voltage-frequency relation, whose behavior depends on the sample angle geometry. The results are reasonably interpreted by the dx2-y2-wave theory by taking the zero energy state into account.

We have developed a measuring system for high-Tc superconducting single-flux quantum circuits and evaluated its performance in terms of bit error rate (BER) measurement for given signal voltage levels. The system includes magnetic shields and a high-frequency test fixture mounted on a closed-cycle cooler. The test fixture is made of non-magnetic material. The transmission characteristics of the measuring system were evaluated by using a vector network analyzer at frequencies ranging from 40 MHz to 20 GHz. The operating temperature of the measuring system ranges from 20 K to room temperature. We connected a 12-GHz wideband pulse amplifier to the system and evaluated its high-speed transmission characteristics. We used a standard 50-Ω microstrip line as an impedance-matched sample. The signal used in the experiment was a 215-1 pseudo random bit signal (PRBS) at 3 Gbps. As a result, the output voltage required for an output driver under the experimental condition was 18.8 mV in order to obtain a resolution of BER measurement of 10-12.

A voltage mode logic device based on RF-Field-driven DC-SQUID (RFDS) using high-TC superconducting Josephson junctions has been proposed. RFDS produces large RF-induced steps, and the orders of steps are strongly selected by DC magnetic flux crossing the SQUID loop superposing with RF magnetic field. In this paper, we present the experimental results of RFDS fabricated by using YBCO grain boundary Josephson junctions. The results are evaluated with numerical simulations. The enhancement of RF-induced steps, the strong selection of step orders and the switching performance are demonstrated.

Recent progress of high-temperature superconductor Josephson junction technology is reviewed in the light of the future application to digital circuits. Among various types of Josephson junctions so far developed, ramp-edge-type junctions with a barrier layer composed of oxide materials in the vicinity of metal-insulator transition seem to offer a unique opportunity to fulfill all the requirements for digital circuit applications by virtue of their small junction dimensions, overdamped properties and relatively high IcRn product values at the temperature of around 30-40 K. Recently developed interface engineered junctions can be classified as junctions of this type. These junctions also raise an interesting problem in physics concerning the possibility of resonant tunneling of Cooper pairs via localized states in the barrier. From the viewpoint of practical applications, the improvement of the spread of the junction parameters is still a serious challenge to the present fabrication technology. Although interface engineered junctions seem to be most promising in this regard at present, 1σ spread of around 8% in the present fabrication technology is far from satisfactory for the fabrication of large-scale integrated circuits. The detailed understanding of the barrier formation mechanism in the interface engineered junction is indispensable not only for advancing this particular fabrication technology but also for improving other junction technology utilizing ramp-edge structures.

A 5-pole lumped element bandpass filter (BPF) of center frequency 264.05 MHz and fractional bandwidth (FBW) 0.76% is designed and fabricated using YBa2Cu3O7-d (YBCO) thin films deposited on both sides of a MgO substrate(40 mm 40 mm 0.5 mm). The return loss, minimum insertion loss and ripple were measured to be 20.0 dB, less than 0.1 dB and less than 0.1 dB at 70 K, respectively. These results verify both the compactness and low loss characteristics in the VHF band. The simulated frequency response, where the frequency dependences of inductance (L) and capacitance (C) elements and housing effect are taken into account, is in good agreement with the measured frequency response.

A portable cryo-system using a high-Tc SQUID for the measurement of the remanant magnetic field of a rock specimen was designed and fabricated. The sensing surface of the SQUID faces upward in our system, although the system for bio-magnetics faces down. The SQUID is cooled by liquid nitrogen via a sapphire heat transfer rod. The total heat transfer of the system was measured by means of a boiling-off method and was found to be 1.65 W. It was demonstrated that the system can be operated for more than 17 hours without any maintenance such as filling with liquid nitrogen. The system was applied to the measurement of the remanent magnetic field distributions of rock samples cored from deep underground. We have successfully measured the distributions.