High-temperature superconductor (HTS) receiving filter subsystem for mobile telecommunication base station has been developed. An 11-pole HTS filter using YBa2Cu3O7-δ (YBCO) thin films and a low noise amplifier were cooled to 70 K by a small cryocooler. Total noise figure of this subsystem was measured to be 0.5 dB. Furthermore the effect of using the subsystem in the receiver front-end of Code Division Multiple Access (CDMA) cellular base station was investigated. The transmitting power reduction of handy terminal was estimated to be about 35%.

The magnetic shielding performance of the high-Tc superconducting (HTS) plate in a mixed state has been investigated numerically. By taking account of the crystallographic anisotropy of the HTS plate, the axisymmetric shielding plate is assumed to have a multiple thin-layer structure. Under the assumptions, the governing equations of the shielding current density can be expressed in terms of a scalar function. The numerical code to integrate the equation has been developed and, by use of the code, the shielding current density and the damping coefficient are calculated for the axisymmetric HTS plate in a mixed state. The results of computations show that the shielding current density localizes around the edge under the high-frequency magnetic field. With an increasing frequency of the applied magnetic field, the localization becomes remarkable and the shielding current density becomes larger until the flux flow occurs. In addition, the magnetic shielding performance of the HTS plate drastically changes with time under the low-frequency magnetic field below 100 Hz, whereas it is almost time-independent under the high-frequency magnetic field. Moreover, it turns out that the HTS plate can shield ac magnetic fields with a high frequency even if it remains in a mixed state.

We describe several properties of very thin stacks of 10 to 20 intrinsic Josephson junctions fabricated on the surface of Bi2Sr2CaCu2O8+δ single crystals. We show that the Joule heating is significantly reduced in these stacks and that the gap structure is clearly observable in the quasiparticle current-voltage (I-V) characteristics. The I-V curves are characterized by a large subgap conductance and a significant gap suppression due to the injection of quasiparticle current. It is found that the IcRn product of these intrinsic Josephson junction stacks is significantly small compared with that expected from the BCS theory. It is also found that there is a tendency that IcRn decreases with increasing c-axis resistivity. Both Ic and the gap voltage exhibit unsaturated temperature dependence at low temperatures. The behavior presents a sharp contrast to that of Josephson junctions made of conventional superconductors. The characteristics are discussed in relation to the d-wave symmetry of the order parameter.

A new or future system of mobile telecommunication is built by new digital technologies to provide an improved and more consistent quality of service for the customers. These digital systems can provide greater number of transmission channel allocation for their subscribers and security. On the digital communication system, distortion of transmitted signal should be eliminated as much as possible for high communication quality. However, the need to both minimize distortion of signal amplifiers and continue to provide good filtering protection can become difficult to achieve with conventional high power amplifiers and filters. In this paper, the application of high-Tc superconducting (HTS) power filters on such digital communication systems and recent progress of filter device developments for those are discussed.

We report the state of the art of superconducting network switching circuits and system technology. Mainly, we describe our switching core circuits and challenges to demonstrate superconducting prototype systems. And also, we review other approach to perform the superconducting digital communication briefly. In our switching core circuits, a ring-pipeline architecture has been proposed and the component circuits of the prototype chips have been fabricated and tested successfully. It is very important to demonstrate the prototype system in order to estimate the total performance of the system with superconducting devices. We have designed a multi-processor system with a superconducting network as a prototype system to demonstrate an interprocessor network system.

Large-area high-temperature superconducting films and damage-free processing techniques have been developed to fabricate low insertion loss and sharp skirt filters for mobile telecommunication. An off-axis-type dc sputtering method was employed to deposit Y-Ba-Cu-O films on both sides of the substrate. The surface resistance of the films was about 0. 35 mΩ(at 70 K and 10 GHz). An 11-pole bandpass receiving filter for the IS-95 telecommunication system was designed and fabricated using 60 mm 50 mm YBCO films on a 0. 5-mm-thick MgO substrate. The passband insertion loss at 70 K was about 0. 1 dB with 0. 1 dB ripple. The third-order intercept point of the filter was 49. 5 dBm. We have assembled the filter and a low-noise amplifier in a dewar with a cryocooler. Ultralow-noise performance (noise figure: 0. 5 dB at 70 K) was presented by the cryogenic filter subsystem.

2-pole band-pass filters (BPFs) with tap-excitation are prepared by using high temperature superconductors (HTS). The possibility of realizing superconducting coplanar filters with attenuation poles is revealed.

New THz radiation devices made of high-Tc superconductors are fabricated and their characteristics are studied in detail. Ultrashort electromagnetic pulses with 0.5 ps width have been radiated into free space from current biased devices made of superconducting YBa2Cu3O7 (YBCO) films by exciting with femtosecond laser pulses. The Fourier spectrum of them extends up to 3 THz. The radiation mechanism is ascribed to the ultrafast supercurrent modulation by the optical pulses. The THz waveform is analyzed using rate equations describing the relaxation of photoexcited quasiparticles. By the improvement of the device structure and the collecting optics, the radiation power can be increased up to 0.5 µW. A new type THz radiation from YBCO films under an external magnetic field without a transport current is also reported.

It is shown that a three-fluid model, which was successfully introduced to explain microwave characteristics of high-Tc superconductors phenomenologically, is suit also to explain those of low-Tc superconductors. In this model, the two contributions of a residual normal electron, in addition to a super and a normal electron in the two-fluid model, and of the temperature (T) dependence of momentum relaxation time τ for the two normal electrons are taken into account. Measured results of the T dependence of surface resistance Rs for a Nb film with critical temperature Tc9.2K agree very well with an Rs curve calculated using the present model, where a residual surface resistance at T0K, Rso, and the T dependence of τ were determined using the surface reactance at 0K Xso37.6mΩ calculated using the BCS theory to fit a calculated Rs curve with the measured values as a function of T. Furthermore, microwave characteristics predicted from the BCS theory cannot be explained phenomenologically using the conventional two-fluid model. This difficulty can be solved by using an improved two-fluid model, called the two-fluid (τ) model, where the T dependence of τ is taken into account. Finally the frequency dependence of Rs calculated for the Nb film is f1.9 for the BCS theory and f2.0 for the three-fluid (τ) model on the assumption of the frequency independence of τ.

Recent progress of highly sensitive magnetmeter utilizing high Tc dc superconducting quantum interference device (SQUID) is reviewed briefly. Performance parameters of the SQUID magnetometer, such as field resolution, dynamic response and usability in unshielded environment, are focused on. Relationship between these performance parameters and SQUID characteristics are discussed quantitatively, and key factors which dominate each performance are clarified. With this result, design principle to obtain high performance SQUID magnetometer operating at T77K is shown. Present status on the performance of the magnetometer is discussed by comparing experimental results with theoretical predictions. Issues to much improve the performance of the high Tc SQUID magnetometer are also discussed.

Ferroelectric / superconducting heterostructures of Pb(Zr0.52Ti0.48)O3 [PZT] / (Y0.6Pr0.4)Ba2Cu3Oy [YPBCO] have been formed on SrTiO3(100) substrate using an ArF pulsed laser deposition. The crystallinity and surface morphology of heterostructures were investigated by X-ray diffraction measurements and atomic force microscopy. We also measured dielectric and ferroelectric properties of PZT film in the Au/PZT/YPBCO structure. Furthermore, we fabricated a three-terminal devices having the structure described above using an in-situ metal mask exchange system, and investigated the ferroelectric field effect. As a result, we observed a modulation of channel resistance approximately equal to that estimated from the induced carrier and memory effect due to remanent polarization of PZT.

We report the strong microwave Josephson radiation from an array of high-Tc junctions on a MgO bicrystal substrate from centimeter- to millimeter-wave ranges. The dc bias current was fed to the junction array having parallel geometry with the pair of junctions shunted by superconducting loops. The configuration of bias leads was a series of interlocking dc SQUID's geometry which guaranteed the oscillation of all junctions at the same frequency. For a five-junctions array, we observed the coherent output power of about 13 pW at receiving frequency fREC22GHz without an external magnetic flux, which was nearly five times higher than that of a single bicrystal junction. We observed the Josephson linewidth of the selfradiation in coherent state less than 1 GHz by the adjustment of the external flux. The phase differences between adjacent junctions with different IcRn products could be controlled by an external small magnetic field. Submillimeter-wave detector response of the five-junction array was also studied experimentally at frequency f478 GHz.

This is a review of our high-Tc superconductor (HTS) sampler development. The design and experimental demonstration of a Josephson sampler circuit based on YBa2 Cu3Ox(YBCO)/PrBa2Cu3Ox/YBCO ramp-edge junctions is described. The sampler circuit contains five edge junctions with a stacked YBCO groundplane and is based on single-flux quantum (SFQ) operations. Computer simulation results show that the time resolution of the sampler circuit depends strongly on the IcRn product of the junction and can be reduced to a few picoseconds with realistic parameter values. The edge junctions were fabricated using an in-situ process in which a barrier and a counter-electrode layer are deposited immediately after the edge etching without breaking the vacuum. The in-situ process improved the critical current uniformity of the junctions to 1σ20% in twelve 4-µm-width junctions. An YBCO groundplane was placed on the junctions in a multilayer structure we call the HUG (HTS cricuit with an upper-layer groundplane) structure. The inductance of YBCO lines was reduced to 1 pH per square without junction-quality degradation in the HUG structure. SFQ current-pulse generation, SFQ storage, and SFQ readout in the circuit have been confirmed by function tests using 3-kHz pulse currents. The successful operation of the sampler circuit has been demonstrated by measuring a signal-current waveform at 50K.

We have developed a strato-mesospheric ozone monitoring system with a low noise SIS mixer, which receives 110.836 GHz millimeter-wave emission due to the rotational transition of ozone molecules (J=61,560,6). The system is completely standalone. We derived the altitude profile of ozone density between 25 km and 80 km from the observed spectrum. The receiver noise temperature was as low as 17 K (DSB), so that the altitude profile could be obtained every 3-10 minutes. The monitoring system can operate continuously over one year without any maintenance work, because it utilizes a 4 K closed cycle helium refrigerator and reliable Nb/AIOx/Nb SIS junctions. We used two acousto-optical spectrometers (AOSs) as real-time spectrometers because of their high resolution and simple construction. In an up-to-date system, one AOS would have a band-width of 65 MHz and the other, a band-width of 250 MHz with resolutions of 40 kHz and 250 kHz, respectively. A computer controls the entire system and is also used to analyze measured data. In this paper, we present the principles of system operation, the latest performance and the construction of the system, and some observed data.

This paper introduces a proto-type model of a superconducting packet switch which is composed of an input buffer, a contention solver, and a distribution network. The contention solver checks for contention by comparing packet addresses while sorting the packets. The input buffer is used for waiting when contention occurs. The distribution network distributes packets which are guaranteed to be contention-free by the contention solver. The design of the proto-type has been completed and the operation has been numerically simulated and confirmed. The elementary circuits of the input buffer, the contention solver, and the distribution network are fabricated by standard Nb tri-layer process and the correct operations are confirmed.

The 4th harmonics of a Nd:YAG laser beam (266 nm) is applied to fabricate highly oriented Y1Ba2Cu3O7-δ -SrTiO3-Y1Ba2Cu3O7-δ multilayer structures. It has been shown that the emission temperature of a film surface will change during deposition, depending on deposition conditions, even though the heater temperature is constant. The change of substrate temperature is strongly correlated to film characteristics such as critical temperature, c-axis length, and resistivity. The insitu monitoring of the substrate temperature is useful for obtaining high-quality Y1Ba2Cu3O7-δ films reproducibly. It is also shown that a SrTiO3 layer prevents oxygen restoration in a Y1Ba2Cu3O7-δ underlayer. The relationship between oxygen deficiency and the annealing conditions is studied.

A high-Tc superconducting filter of the planar structure is proposed for handling higher power signals and for miniaturizing the filter configuration. The filter is designed with a single disk-resonator shared by two degenerate modes to operate as a two-stage bandpass filter. Thereby the proposed filter is expected to possess high power handling capability as a conventional filter with two resonator disks does while the filter configuration is about a half in area compared to the conventional one. The Tchebyscheff type filter with 5.1 GHz center frequency and 2% relative bandwidth was fabricated using a high-Tc superconducting thin film. The passband insertion loss, Lo, was approximately 0.8 dB at 77 K. The low loss performance due to the superconductivity was observed at incident signal levels up to 41.2 dBm (around 15 W) at 20 K, which is limited by the power devices in the measurement setup. In addition, good linearity in the filter responses was confirmed by observing the intermodulation distortion with the two-tone method, which indirectly shows a stable operation with higher power incident signals.

We have studied the performances of several types of vortex flow transistors including prototype flux flow transistors (FFTs), nanobridge vortex flow transistors (NBVFTs) based on a parallel array of nanobridges, planar Josephson vortex flow transistors (planar JVFTs) based on a parallel array of grain boundary Josephson junctions, and JVFTs with a stacked structure (stacked JVFTs). The NBVFTs had considerably higher magnetic field sensitivity and shorter response time than the FFTs. A flux-to-voltage transfer function V/φ of 2.6 m V/φo and a modulation depth of 0.5 mV were obtained for the NBVFT composed of 2 nanobridges, while the current gain was small. The temperature dependence of the device parameters (the dynamic resistance and the inductance) suggests that the surface barrier to the Abrikosov vortex entry into the nanobridge strongly contributes to the relatively large V/φ values. The response time of the nanobridge is estimated to be 5 ps. On the other hand, the JVFTs showed large current gains because of the small kinetic inductance of the Josephson junction. The planar JVFT composed of 3 Josephson junctions with an asymmetrical geometry showed a current gain of 2.2 at 4.2 K. Also, the stacked JVFT showed the current gain of 2.0, while the maximum value of V/φ was 210 µV/φo. The mutual inductance between the control line and the superconducting loop within the transistor was enhanced in the stacked JVFT. This enhancement may yield a short response time compared to that of the planar JVFT. When we apply these vortex flow transistors, we should take account of the properties peculiar to each transistor.

Here we report on a fabrication and a millimeter-wave performance of reliable and reproducible high-Tc superconducting (HTS) Josephson junctions on MgO substrates using a focused Ga ion beam (FIB). The junction normal resistance Rn can be controlled by making the junction in a series. The Rn depends on space between each junction in the series structure. A mechanism of the junction is proposed by measuring cross-sectional transmission electron microscopy (TEM) images and their X-ray spectra of Ga, Y, Ba, Cu, Mg and O. The junctions with more than 1 µm spaces, and flat and lateral structure are independent each other for the crystallization process. We observe the HTS mixer-antenna performance as fundamental/harmonic mixers in the wide frequency range up to 100 GHz.

This paper describes analytical results of high-Tc superconducting asymmetric coplanar strip lines using the frequency-dependent finite-difference time-domain method. The propagation constants of the YBa2Cu3O7-x asymmetric coplanar strip line fabricated on the LiNbO3 substrate are reported. The effect of the SiO2 buffer layer is also investigated.