We describe the development of single-flux-quantum (SFQ) microprocessors and the related technologies such as designing, circuit architecture, microarchitecture, etc. Since the microprocessors studied here aim for a general-purpose computing system, we employ the complexity-reduced (CORE) architecture in which the high-speed nature of the SFQ circuits is used not for increasing processor performance but for reducing the circuit complexity. The bit-serial processing is the most suitable way to realize the CORE architecture. We assembled all the best technologies concerning SFQ integrated circuits and designed the SFQ microprocessors, CORE1α, CORE1β, and CORE1γ. The CORE1β was made up of about 11000 Josephson junctions and successfully demonstrated. The peak performance reached 1400 million operations per second with a power consumption of 3.4 mW. We showed that the SFQ microprocessors had an advantage in a performance density to semiconductor's ones, which lead to the potential for constructing a high performance SFQ-circuit-based computing system.

We have designed a superconductor-semiconductor hybrid analog-to-digital (A/D) converter and experimentally evaluated its performance at sampling frequencies up to 18.6 GHz. The A/D converter consists of a superconductor front-end circuit and a semiconductor back-end circuit. The front-end circuit includes a sigma-delta modulator and an interface circuit, which is for transmitting data signal to the semiconductor back-end circuit. The semiconductor back-end circuit performs decimation filtering. The design of the modulator was modified to reduce effects of integrator leak and thermal noise on signal-to-noise ratio (SNR). Using the improved modulator design, we achieved a bit-accuracy close to the ideal value. The hybrid architecture enabled us to reduce the integration scale of the front-end circuit to fewer than 500 junctions. This simplicity makes feasible a circuit based on a high TC superconductor as well as on a low TC superconductor. The experimental results show that the hybrid A/D converter operated perfectly and that SNR was 84.8 dB (bit accuracy~13.8 bit) at a band width of 9.1 MHz. This converter has the highest performance of all sigma-delta A/D converters.

We have developed the fabrication process, the circuit design technology, and the cryopackaging technology for high-Tc single flux quantum (SFQ) devices with the aim of application to an analog-to-digital (A/D) converter circuit for future wireless communication and a sampler system for high-speed measurements. Reproducibility of fabricating ramp-edge Josephson junctions with IcRn products above 1 mV at 40 K and small Ic spreads on a superconducting groundplane was much improved by employing smooth multilayer structures and optimizing the junction fabrication process. The separated base-electrode layout (SBL) method that suppresses the Jc spread for interface-modified junctions in circuits was developed. This method enabled low-frequency logic operations of various elementary SFQ circuits with relatively wide bias current margins and operation of a toggle-flip-flop (T-FF) above 200 GHz at 40 K. Operation of a 1:2 demultiplexer, one of main elements of a hybrid-type Σ-Δ A/D converter circuit, was also demonstrated. We developed a sampler system in which a sampler circuit with a potential bandwidth over 100 GHz was cooled by a compact stirling cooler, and waveform observation experiments confirmed the actual system bandwidth well over 50 GHz.

The utilization of a high-Tc superconductor for implementing a superconducting qubit is to be expected. Recent researches on the quantum property of Josephson junctions in high-Tc superconductors indicate that the low energy quasiparticle excitation is weak enough to observe the macroscopic quantum tunneling. Therefore, a detailed study on the quantum property of high-Tc Josephson junctions becomes more important for applications. We show our experimental results of the macroscopic tunneling of current biased intrinsic Josephson junctions in Bi-2212 and its resonant activation in the presence of microwave radiation.

Single flux quantum (SFQ) circuit elements have been designed and fabricated using the YBa2Cu3O7-δ ramp-edge junction technology. Logic operations of SFQ circuit elements, such as a toggle flip-flop (T-FF), a set-reset flip-flop (RS-FF), and a 96-junction Josephson transmission line (JTL), were successfully demonstrated, and dc supply current margins were confirmed up to temperatures higher than 30 K. The circuit layout was improved in order to suppress the critical current (Ic) spread that appears during the junction fabrication procedure. By employing the new circuit layout rule, correct operations at temperatures from 27 K to 34 K with dc supply current margins wider than 7% were confirmed for the T-FF with a single output. Moreover, the maximum operating frequencies of T-FFs were measured to be 360 GHz at 4.2 K and 210 GHz at 41 K, which are substantially higher than the values for the circuits with the conventional layout. According to the simulation result, the maximum operating frequency at 40 K was expected to be approximately 50% of the characteristic frequency at a bit error rate (BER) less than 10-6.

We report on a subsystem of electromagnetic wave radiation and propagation estimation using high-Tc superconducting (HTS) receiving filters for S band. The subsystem, comprised of HTS filters, a rubidium standard signal generator (Rb SSG), a global positioning system (GPS) unit, etc., was used to evaluate the electromagnetic-wave (EMW) intensities, frequencies, the frequency interferences and the ground positions where the EM are measured. The developed subsystem showed high frequency selectivity for S band by using the HTS filters. Furthermore, we verified that the subsystem with the HTS filters operated on the moving car.

We describe three types of software-defined-radio (SDR) receivers based on superconducting technologies. The superconducting analog bandpass filters are essential for all types of the receivers. Another key component is an analog-to-digital converters (ADCs), which are required to have high resolution with a broad band width. The complementary Δ ADC based on the single-flux-quantum circuit is a promising candidate for the SDR receivers because it has a practical nature together with above-mentioned requirements. The experimentally obtained signal-to-noise ratio (SNR) and sensitivity, which are closely related to the resolution, are 34 dB and 20 µA for a quarter of the full-scale input with a band width of about 20 MHz. If we use the optimum decimation filter, the ADC is expected to have the SNR of 82 dB and the sensitivity of 300 nA. These values meet the requirements of the easiest type of the SDR receiver. After new fabrication process has been introduced and the architecture of the ADC has been improved, all types of recievers could be realized based on superconductors.

A system was developed to measure the microwave power dependence of the surface resistance superconductor films. The system uses a dielectric resonator method combined with a circle fit technique and a two-mode technique to measure the microwave surface resistance of superconductor films. For validation, this system was used to measure such surface resistance for superconductor films with different surface morphologies. Significant difference in microwave power dependence of surface resistance was observed. This measurement system proved suitable for evaluating superconducting films for passive microwave devices, including high power devices such as transmitting filters.

A novel high temperature superconducting interdigital bandpass filter is proposed by using coplanar waveguide quarter-wavelength resonators. The CPW resonators are arranged in parallel, and consequently the filter becomes very compact. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0 GHz and an equal-ripple fractional bandwidth of 3.2%. It is fabricated using a YBCO film deposited on an MgO substrate. The measured filtering characteristics agree well with EM simulations and show a low insertion loss in spite of the small size of the filter.

A dielectric resonator with a gap between the top plate and the rest has been useful for measuring the penetration depth (λ) of superconductor films, a parameter essential for obtaining the intrinsic microwave surface resistance (Rs) of thin superconductor films. We investigated effects of a gap on the microwave properties of TE0ml-mode sapphire resonators with a gap between the top plate and the rest of the resonator. Regardless of a 10 µm-gap in TE0ml-mode sapphire resonators, variations of the TE0ml-mode resonant frequency on temperature (Δf0) as well as TE0ml-mode unloaded Q remained almost the same due to lack of axial currents inside the resonator and negligible radiation effects. The λ of YBa2Cu3O7-δ (YBCO) films obtained from a fit to the temperature-dependent Δf0 appeared to be 195 nm at 0 K and 19.3 GHz, which was well compared with the corresponding value of 193 nm at 10 kHz measured by the mutual inductance method. The intrinsic Rs of YBCO films on the order of 1 mΩ, and the tan δ of sapphire on the order of 10-8 at 15 K and 40 GHz could be measured simultaneously using sapphire resonators with a 10 µm-gap.

Two types of miniaturized high-temperature superconducting filters are described in this paper. The first type is developed by using small-sized microstrip spiral resonators, and the second type by coplanar waveguide quarter-wavelength resonators. The filters have significantly reduced size compared with many previous HTS filters. They are designed by employing an electromagnetic simulator in combination with appropriately chosen equivalent circuits. Their measured frequency responses agree well with theoretical predictions, and show low insertion losses in spite of their small sizes.

We have fabricated a multilayer structure for single flux quantum (SFQ) circuit application using a high-temperature superconductor (HTS). La0.2-Y0.9Ba1.9Cu3Ox (La-YBCO) base electrode layers were prepared by a dc or rf magnetron sputtering method. The reproducibility of film quality for dc-sputtered La-YBCO films was better than that for rf-sputtered films, and the dc sputtered films exhibited the average surface roughness Ra less than 1.0 nm and a Tc zero value of 88 K. By using the dc-sputtered La-YBCO films, a multilayer structure of SrSnO3/La-YBCO/SrSnO3/La-YBCO on MgO substrate with Ra below 2.0 nm was obtained. Interface-modified ramp-edge junctions with La0.2-Yb0.9Ba1.9Cu3Ox (La-YbBCO) counter electrodes have been fabricated by using this multilayer structure with dc-sputtered films. The fabricated junctions exhibited RSJ-type I-V characteristics with IcRn products of about 3 mV at 4.2 K. We also obtained a 1-σ Ic spread of 8% for a 1000-junction series-array. The sheet inductance values at 4.2 K for the base and counter electrodes on La-YBCO ground planes were 0.8 pH and 0.7 pH per square, respectively. Operation of several types of elementary SFQ circuits has been successfully demonstrated by using this multilayer structure.

To enable the use of passive transmission lines (PTLs) for the interconnection of single-flux-quantum (SFQ) circuits, we have implemented a driver and a receiver and have developed a method for designing SFQ circuits with passive interconnections. Basic components and properties of passive interconnections, such as the frequency characteristics of the driver and receiver, the PTL delay, and the crosstalk between PTLs, have been experimentally verified. Our developed components and design method have been applied to actual SFQ circuits, such as a 44 switch having block-to-block passive interconnections and a 22 switch having gate-to-gate passive interconnections. We have also shown the advantages of PTLs over Josephson transmission lines (JTLs). We also discuss the prospects of SFQ circuits having passive interconnections.

2 GHz band electrically tunable superconducting microstrip line band-pass filter was developed. The tunable filter used a thin interdigital electrode. The dielectric distribution of SrTiO3 substrate included a calculated nonlinear effect of the electrode and ferroelectric material. As a result, the tunable microstrip line filter design with interdigital electrode enabled calculation by the finite element method and the moment method. The tunable filter with a measured unloaded Q factor of 9700 and a frequency shift of 1.25 MHz was obtained.

There is a possibility that individuals ingest contaminants that have been accidentally mixed with food because processed foods have become very common. Therefore a detection method of small contaminants in food and pharmaceuticals is required. High-Tc SQUID detection systems for metallic contaminants in foods and drugs have been developed for safety purposes. We developed two systems; one large system is for meat blocks and the other small system is for powdered drugs or packaged foods. Both systems consist of SQUID magnetometers, a permanent magnet for magnetization and a belt conveyor. All samples were magnetized before measurements and detected by high Tc SQUIDs. As a result, we successfully detected small syringe needles with a length of 2 mm in a meat block and a stainless steel ball as small as 0.3 mm in diameter.

A high temperature superconductor (HTS) filter is designed and measured at 1.93 GHz, using microstrip half-wavelength spiral resonators. Resonant and coupling characteristics of miniaturized microstrip spiral resonators are investigated first. Then a 4-pole Chebyshev bandpass filter with a very narrow passband (4.1 MHz) is designed and realized using microstrip spiral resonators. The filter is fabricated using HTS YBCO films deposited on a LaAlO3 substrate. The measured frequency response of the filter agrees reasonably with the specifications, and shows that the filter owns excellent property of spurious resonance rejection over a wide frequency range.

At frequencies currently used by mobile communications, many of the microstrip half-wavelength resonators are too large to realize miniaturized filters. For this reason, very small-sized microstrip spiral resonators and filters, using high-temperature superconductors (HTS), have been studied recently. In this paper, the resonant and coupling characteristics of microstrip G-type and S-type spiral resonators are investigated first by using an electromagnetic simulator. Then small-sized 4-pole, 8-pole, and 16-pole Chebyshev bandpass filters using S-type spirals are designed, respectively, with a midband frequency f0 = 1.93 GHz. The frequency responses of the filters satisfy well the desired specifications, and the measured frequency response of the 8-pole HTS filter agrees well with the theoretical prediction.

Precise designs are presented for sapphire rod resonators of three types, which have been proposed by the IEC/TC90/WG8 in the standard measurement method of the surface resistance Rs of high-Tc superconductor (HTS) films; an open-type, a cavity-type and a closed-type. In order to separate TE011 and TE013 modes, which are used in Rs measurements, from the other modes, appropriate dimensions for these three resonators are determined from mode charts calculated from a rigorous analysis based on the mode matching method, taking account of an uniaxial-anisotropic characteristic of sapphire. Comparison of the open-type resonator with the closed-type is performed. For the open-type, the unloaded Q values of both the TE011 and TE013 modes are reduced by radiations of a leaky state TM310 mode. Finally, validity of the design and a two-sapphire-rod-resonator method will be verified by experiments.

The present state of IEC and JIS standards is reviewed on measurement methods of low-loss dielectric and high-tempera-ture superconductor (HTS) materials in the microwave and millimeter wave range. Four resonance methods are discussed actually, that is, a two-dielectric resonator method for dielectric rod measurements, a two-sapphire resonator method for HTS film measurements, a cavity resonator method for microwave measurements of dielectric plates and a cutoff circular waveguide method for millimeter wave measurements of dielectric plates. These methods realize the high accuracy sufficient for measurements of temperature dependence of material properties.

An important barrier to the application of high-temperature superconducting microwave filters is their power-handling capability. To clarify the key parameters for improving the power-handling capability of rf filters based on high-temperature superconductors with microstrip structures, we synthesize bandpass filters with different layouts using several kinds of thin film high-temperature superconductors, and subject them to third-order intermodulation measurements. By improving the sensitivity of the measurement set-up through the selective reduction of the fundamental output signals, we succeed in measuring the intermodulation signals of the superconducting filters. The experimental results indicate that increasing the film thickness and utilizing MBE-grown films of NdBa2Cu3O7 films are effective in obtaining high-power handling microstrip filters.