A calculation method by the improved three-fluid model is shown to describe phenomenologically temperature and frequency dependence of surface resistance Rs for high-Tc superconductors. It is verified that this model is useful to describe temperature dependence of Rs for such high-Tc superconducting films as Y-Ba-Cu-O (YBCO), Eu-Ba-Cu-O, and Tl-Ba-Ca-Cu-O films. For the frequency dependence of Rs of a YBCO bulk, furthermore, the measured results which have not depended on f2 in the frequency range 10-25 GHz, can be described successfully by this model. Finally, a figure of merit is proposed to evaluate material quality for high-Tc superconductors from the values of electron densities and momentum relaxation time determined by the present model.

High-Tc superconducting flux flow transistors were fabricated with co-evaporated thin films of YBaCuO. The vortex flow channels (2 µm in width) and the device patterns were formed by Ar ion milling. The three-terminal characteristics, vortex flow characteristics, transresistance, and current gain of the device were measured. The AC input-output characteristics of the device with an Au load resistor were also measured. The measured flow voltage, transresistance and current gain are discussed in relation to these AC input-output measurements.

The capacitance and the resistance of the Au/PrBa2Cu3Oy (PBCO)/YBa2Cu3Ox (YBCO) structure were measured at liquid helium temperature. A film of YBCO was deposited by rf magnetron sputtering at 700, and its thickness was 250 nm. A film of PBCO was deposited by rf magnetron sputtering at 690, and its thickness was less than 375 nm. The inverse capacitance and the resistance of the structure increased with PBCO thickness when PBCO thickness was more than 70 nm. However, the inverse capacitance was near zero, and the resistance was much less than that of PBCO itself when PBCO thickness was less than 70 nm. These results show the possibility that the electric property of PBCO within 70 nm from the PBCO/YBCO interface is different from that of PBCO itself, that is, there is a low-resistance region in PBCO near the YBCO/PBCO interface.

The paper discusses properties of YBaCuO thick films produced by screen printing method and followed sintering of a paste made from pre-annealed powder on Yttrium Stabilized Zirconia (YSZ) and MgO substrates. The prepared films have been studied by X-ray diffraction, scanning electron microscopy (SEM) and resistance vs. temperature measurements.

A superconducting multichip module using Nb/Polyimide on a mullite multilayer ceramic substrate has been developed for Josephson LSI circuits. The Nb/Polyimide stacked layers on the mullite multilayer ceramic substrate makes it possible to fabricate superconducting off-chip wiring for control signal line. We named the MCM "SuperMCM". The superconducting transmission line is designed to have the characteristic impedance of 14 Ω to match with the Josephson devices. The superconducting critical temperature, critical current density and critical current at a via hole are 8.5 K, 8.2105 A/cm2 and 2.5 A, respectively. The SuperMCM also provides matching circuits employing quarter wavelength striplines for driving Josephson LSI circuits at a microwave frequency, and DC bias circuits in the mullite multilayer ceramic substrate. The characteristics of the matching circuit is measured in the frequency range up to 3.6 GHz and the microwave current gain of 20 dB is obtained at 1.2 GHz, which revealed that the SuperMCM has the ability to drive the Josephson LSI circuits at more than 1.2 GHz clock speed.

Step-edge Josephson junctions (SEJJs), which are made by YBa2Cu3O7 (YBCO) thin films on MgO (100) substrates with gentle step angle (below 40 degrees) have been successfully fabricated. The step-edge, with several angles on the MgO substrate, were made using photolithography and Ar ion beam etching, and then YBCO films were deposited on the step-edges by pulsed laser deposition method. The relationships between step-angles and I-V characteristics, microwave properties and structure of SEJJs were systematically investigated. Shapiro steps were clearly observed only in step-angle range between 10 and 30 degrees. Intermittence and hysteresis on the I-V characteristics were observed above 30 mA without effect from step-angles.

A multi-channel high temperature superconducting interference device (high Tc SQUID) system with high magnetic field resolution has been developed. Step edge junctions were employed as weakly coupled Josephson junctions for the SQUID. These junctions worked well and their I-V curves fit the resistively shunted junction (RSJ) model. The SQUID design was investigated to improve magnetic field resolution. The size of the SQUID's center hole was investigated, and we found the optimized size of the hole to be about 25 µm. Meissner effect of superconductor was used in order to concentrate magnetic fluxes. A large washer SQUID and a flux concentrating plate was developed to concentrate magnetic flux to the SQUID center hole. The magnetic field resolution became 370 fT/Hz at 10 Hz and 220 fT/Hz at 10 kHz. This field resolution was enough to detect biomagnetic signals such as magnetocardiac signals. The SQUID was mounted on a special chip carrier and was sealed with epoxy resin for protection from humidity. We have designed and developed a 4-channel and a 16-channel high Tc SQUID system. We used them in a magnetically shielded room to measure magnetic signals of the human heart. We obtained clear multi-channel magnetocardiac signals, which showed clear so called QRS and T wave peaks. A clear isofield contour map of magnetocardiac signals was also obtained. These data indicated that high Tc SQUID is feasible for these biomagnetic applications.

This paper describes a new method for joining BiSrCaCuO superconductors (BSCCO) which realizes low microwave loss and high mechanical strength. This method consists of two processes. In the first the BSCCO surface is metallized with Ag and in the second a joint is formed by using thermally curable Ag paste. With this method, we obtained a joint with a loss of 0.3 dB around 1.1 GHz with the co-axial cavity techniques. Furthermore, the mechanical strength of the joint was greater than that of the BSCCO sample. From the results of DC resistance measurements and SEM observations, we attribute this good performance to the adhesion and continuity of the metallized Ag with the BSCCO surface.

A YBCO/CeO2/Au MIS structure (YBCO:YBa2Cu3O7y) is fabricated on a MgO(100) substrate with the help of the all-in-situ electron-beam and heater coevaperation system. The current-voltage (I-V) characteristics of the deposited YBCO film under various gate voltages are examined. Small modulation of the I-V characteristics by gate voltages can be observed. Meanwhile, the surface morphology is also studied by means of an atomic force microscope (AFM). The relation between the field effect and the surface morphology of a thin YBCO film is discussed.

Bi2Sr2Ca1Cu2Ox thick film superconducting shields have been fabricated for use with HTc SQUIDs. Shielding factors and internal noise levels of the shields were measured using a DC SQUID magnetometer. A sample in which BSCCO was coated on the outside of a cylindrical Ag substrate exhibited larger noise levels than that with a sample in which BSCCO was coated on the inside of the Ag cylinder. The difference is explained by the thermally driven (Johnson) noise from the Ag substrate. A sample with the Ag cylinder outside the superconductor and samples with MgO substrates inside the superconductor showed good performance with a shielding factors of 10-8 and internal noise levels which did not exceed the DC SQUID magnetometer resolution (5 fTrms/Hz) at 4.2 K. In addition, the flux relaxation noise of BSCCO superconducting shields was estimated from the relaxation behavior of BSCCO.

Bi2Sr2CuOx (Bi(2201)) thin films have been fabricated by atomic layer-by-layer deposition using ion beam sputtering (IBS) method. During the deposition, 14 wt%-ozone/oxygen mixture gas of typical pressure of 5.010-5 Torr is supplied with ultraviolet light irradiation for oxidation. XRD and RHEED investigations reveal that a buffer layer with compositions different from Bi(2201) is formed at the early deposition stage of less than 10 units cell and then Bi(2201) oriented along the c-axis is grown.

In order to explain the temperature and frequency characteristics of high-Tc superconductors, a new model is proposed, which will be called the improved three-fluid model, where the momentum relaxation time τ is assumed to depend on temperature in the superconducting and normal states, respectively, although τ has been assumed to be independent of temperature for the conventional three-fluid model. According to this model, the complex conductivity σ1jσ2 and the surface impedance ZsRsjXs, where Rs is the surface resistance and Xs is the surface reactance, are expressed as a function of temperature. The temperature dependences of Zs and for a YBCO bulk estimated using this model agree very well with ones measured by the dielectric-loaded cavity method in room to cryogenic temperature. In particular, a peak of σ1 observed just below the critical temperature Tc in experiments, appeared in the calculated results based on this model. This phenomenon has been already known in the BCS theory. Thus, it is verified that this model is useful to explain the microwave characteristics of high-Tc superconductors in room to cryogenic temperature. On the other hand, the residual normal electron density nres4.2541023 m-3 and the total electron density nt7.3081024 m-3 are obtained by calculation. The ratio nres/nt0.058 can be used as figure of merit to evaluate material quality of high-Tc superconductors; thus it means that there is 5.8% nonpairing electron in this YBCO bulk.

The barrier-layer was successfully fabricated for a preparation of tunneling junction using high Tc oxidesuperconductor such as Bi-Sr-Ca-Cu-O system. Bi2Sr2Ca2Cu3Ox films were used for both superconducting electrodes and the barrier was mainly Bi2Sr2CaCu2O and the rest that was formed by effects of de-calcium from the first sputtered (2223) film. The reaction of de-calcium occurred immersing it in carbonated water. The change of (2223) phase of BSCCO was confirmed with a comparison of the intensity of X-ray diffraction. The superconductive transition temperature of the junction is different from that of the single film (2223) which had no treatment with carbonated water. Zero-bias-currents through fabricated barrier are observed and the critical currents depend on temperature so far as measured temperature region of 79 K-72 K.

The Cooper pairing interaction in high Tc oxide superconductor is discussed in terms of an empirical expression; TcDexp[1/g], gcωo which was derived in our previous investigation. The dual character of this expression consisting of the phonon Debye temperature D and electronic excitation ωo in the mid-infrared region can be interpreted on the basis of the phonon-assisted mechanism on carrier conduction and the electronic excitation. A tunneling spectrum here presented shows certain evidence of the phonon contribution. The characteristics of the long range superconductive proximity phenomena recently reported are also may be interpreted by this mechanism.

A Chebyshev type bandpass filter using four TM01δ-mode dielectric rod resonators oriented axially in a high-Tc superconductor cylinder is designed with 3 dB bandwidth 36 MHz at 11.958 GHz. The single resonator which contains a Ba (MgTa) O3 ceramic rod of εγ=24 and a YBa2Cu3Oy bulk cylinder is designed to realize temperature coefficient of f0, τf=0 ppm/K at 20 K. The unloaded Q, Qu measured at 20 K is 150,000 which is higher than Qu=100,000 for a TM01δ-mode resonator with a copper cylinder. When the constructed filter is cooled from room temperature to below 50 K, the center frequency shifted only 5 MHz which corresponds to τf=1.5 ppm/K and the insertion loss IL0 at the center freqency reduced from 3.0 dB to about 0 dB, the designed value of which is 0.04 dB, which is too small to be measured accurately.

This paper describes the properties of non-dispersive and dispersive delay lines fabricated using EuBaCuO superconducting films. The 24 cm long stripline non-dispersive delay line showed a very low loss of 0.3 dB/nsec at 77 K and 10 GHz, and no dispersion at a delay time of 2.3 nsec at frequencies below 20 GHz. The 14 cm long microstrip dispersive delay line with modal dispersion exhibited a relative delay time of approximately 120 psec in the 118 GHz frequency range. The 26 cm long stripline dispersive delay line with structural dispersion due to coupling provided a relative delay time of 230 psec in the above frequency range and roughly the same loss as a non-dispersive delay line.

Thin-film YBCO Josephson junctions were successfully fabricated by a pulsed excimer laser ablation, and the mixing experiments in the microwave region (820 GHz) were carried out at the temperature of 77 K. The IF output maximum was obtained at the bias voltage midway between the zero and the first Shapiro steps for the fundamental mixing. For the 2nd harmocic mixing, the IF output maximum was obtained at a zero bias voltage, and the conversion efficiency was -14 dB at the microwave frequency of 18 GHz. These results strongly suggest that the fabricated thin-film Josephson junctions work well at the temperature of 77 K as detectors and mixers in the microwave regions (820 GHz).

We have fabricated superconducting microwave passive components such as resonators, bandpass filters and delay lines with YBCO thin film conductors deposited on MgO substrates. Considerably high unloaded Q values of 12000 at 5.5 GHz was obtained with the YBCO microstrip resonator at 77 K, which indicated that the surface resistance of the YBCO thin film was 0.79 mΩ at that frequency and temperature. Excellent microwave properties were also demonstrated with the bandpass filter and the delay line. Considerably low insertion loss of about 1 dB was obtained with the 10 GHz YBCO bandpass filters at 77 K which have a various bandwidth from 0.5% to 10%. Also excellent microwave propagation was obtained with a 1.3 nsec YBCO coplanar delay line. Its insertion loss was less than 1 dB for the frequencies up to 4 GHz.

Sandwich-type Josephson junctions with the structure Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz (BSCCO/BSCO/BSCCO), have been fabricated and their characterstics determined. The BSCO barrier layer, which is characterized by a crystal structure close to that of the BSCCO electrode layer, is a normal conductor at 4.2 K. Superconductor/normal-conductor/superconductor (S/N/S) type current-voltage characteristics are obtained with these junctions. Distinctive Shapiro steps are observed when they are exposed to microwave radiation. An oscillating behavior of each step in their I-V characteristics are confirmed for increased microwave power. The critical current, Ic, is found to be proportional to (1-T/Tc)2 in the neighborhood of Tc. These results coincide with the ones observed with conventional S/N/S junctions.

Among the many fabrication methods for oxide superconductor films, metal organic chemical vapor deposition (MOCVD) is particularly suitable for industrial application because of its mass productivity and the low growth temperature. Therefore we have studied this technique using the horizontal cold wall furnace type MOCVD method to obtain high quality superconducting films. As the result, we have succeeded in fabricating YBa2Cu3Oy films which have high critical temperatures (over 80 K) under substrate temperatures as low as 700 without post-annealing. But, in the course of our experiments, it was found that the thicknesses of YBa2Cu3Oy films fabricated by MOCVD were not uniform. The cause of this non-uniformity is believed to be that the deposition rate exponentially falls off along the flow direction because of the decrease of the source gas concentration through the reaction. In this paper, this non-uniformity is analytically studied. It is shown that the deposition rate decrease can be controlled with a tapered inner tube, and that these theoretical results are in good agreement with the results of experiment. In addition, it is indicated that the superconducting property of the films has less dependence on substrate position as a result of the tapered inner tube.