In situ grown Y-Ba-Cu-O films were prepared on MgO substrate by rf magnetron sputtering with dc-biased substrate holder using a stoichiometric YBa₂Cu₃O_z target. The films were deposited at substrate temperature T_s about 660 and various substrate holder bias voltages V_H. Influence of a dc bias voltage of substrate holder on the superconducting characteristics of Y-Ba-Cu-O thin films are investigated. Films with critical temperature higher than 80 K can be obtained at bias voltages from 20 V to 80 V for 500 mTorr. The optimum bias voltage to obtain the high T_c films depends on the sputtering gas pressure. The optimum bias voltages in 500 mTorr and 300 mTorr are 20 V and 150 V, respectively. The film morphology depends on the bias voltage rather than the sputtering gas pressure in this experiment and the smooth film surface is obtained at low voltages from 20 V to 40 V. For the films deposited at 80 V in 500 mTorr, the film of 200 nm thick is smoother than films of 400 nm and 700 nm thick. The deviation of the film composition is varied by the negative holder bias voltage. The critical temperature depends on the c-lattice parameter rather than the film composition. The films with short c-lattice parameter have the high T_c. The negative holder bias is effective for obtaining the high T_c films in the low pressure. However, in the high pressure, the films at the high bias voltages have slightly low T_c as compared with films at low bias voltage.

Rapid thermal annealing of sputter-deposited Y-Ba-Cu-O (YBCO) films is investigated. Annealing above 980 results dominantly the decomposition reaction of YBCO, but annealing at 960 for 2 min yields the crystallization of YBCO to low-T_c phase which has c-axis preferred-orientation to MgO substrates. T_{c end} of the films were about 60 K. Superconducting YBCO films are also obtained on ZrO₂/Si substrates by rapid thermal annealing at 940 for 5 sec and holding at 500 for 5 min.

The highly reliable epitaxial YBaCuO films have been obtained by the high-pressure reactive sputtering. The highest zero resistance temperature T_c0 of the in-situ grown film was 89.3 K. The c-axis lattice constant, T_c0 values, deposition rate and reproducibility were systematically investigated with respect to the discharge gas pressure. A simple model of the high-pressure sputter deposition was given, which reasonably explained the dependence of the deposition rate on the gas pressure and target-substrate spacing.

Au/Bi-Sr-Ca-Cu-O (BSCCO) were prepared by evaporating Au on the air-cleaved surfaces of 80 K-phase BSCCO single crystals and heating in Ar gas. The electrical contact resistance of the Au/BSCCO specimen decreased by heating at 400 in Ar gas. From the depth profiles of the specimens by X-ray photoelectron spectroscopy, we found that there was a reaction region (Ar⁺-sputter etching time is 0 to 2 min (20 )) on the surface of the Au/BSCCO specimen heated at 400, where Au diffused into the bulk of the BSCCO single crystals. The reaction region is thought to cause the decrease of the electrical contact resistance of the specimen.

The superconducting bridges with constrictions as small as 0.5 µm were fabricated by high-quality Ba₂YCu₃O_x thin films on silicon with buffer layers. The observed I-V characteristics of this bridge could be successfully analyzed by the modified form of Aslamazov and Larkin theory which shows that our microbridge junction is a homogeneous wide superconducting bridge and the characteristics of this bridge are not dependent on the defects such as grain boundaries of the film.

High-Q end-coupled half-wave coplanar line resonators are fabricated by using EuBa₂Cu₃O_7-δ film sputtered on a MgO substrate. The maximum loaded Q value is 4500 and the unloaded Q value is 12500 at 28 K and 3.9 GHz. The surface resistance R_s is estimated from the Q values and the lowest R_s value is 28 µΩ at the same temperature and frequency. This value is two orders of magnitude lower than that of Cu. The minimum R_s sensitivity in the measurement with a coplanar resonator is also discussed. The estimated sensitivity is lower than 10 µΩ below 10 GHz.

A new conduction mechanism of high-T_c superconductors is proposed to interpret experimental results phenomenologically, which will be called a three-fluid model, since nonpairing residual normal electron density n_res is added into the super electron density n_s and the normal electron density n_n for a well-known two-fluid model. According to this model, an admittance equivalent circuit of superconductor in unit cube is derived and n_n, n_s, the complex conductivity , the surface impedance Z_s, the skin depth δ, and the penetration depth λ are expressed as a function of temperature. Also such electron densities as n_s, n_n, and n_res are expressed as a function of Z_s. For Z_s, , δ, λ, n_n, and n_s of a YBCO plate, the values calculated by this model agree well in the range T0.9 T_c with the ones measured by the dielectric resonator method, where T_c is the critical temperature; thus the validity of this model is verified. Also the ratio n_res/n_t0.18 is determined by using n_res1.710²⁴ m^-3 and n_t9.510²⁴ m^-3 obtained from the measured Z_s values; thus it means that there is 18% nonpairing electron density in this YBCO plate. The ratio n_res/n_t can be used as figure of merit of high-T_c superconductors.

The transport properties of low energy quasi-particles across the base layer in superconducting base transistors has been described using the Boltzmann equation which is based on the BCS theory. In order to investigate these transport properties, the Boltzmann equation was solved by means of the Monte-Carlo method which includes the acoustic phonon scattering mechanism. For the isotropic Nb system at 3 (K), a large mean-free path of L6.710^-2 (cm) and a diffusion coefficient of D2.510⁵ (cm/s) were obtained. The base layer transit time was estimated to be about 0.3 (ps) for a 1000 () thin Nb base at 3 (K). We also applied this method in the case of the oxide high-T_c superconductor YBa₂Cu₃O₇, by modifying the corresponding parameter value.

A new high speed switch module was constructed using a high temperature superconducting bulk core (YBa₂Cu₃O_7-x or Bi₂Sr₂CaCu₂O₈) in the liquid nitrogen and two switching transistors having maximum rate of 1 A. The main part of the module is the Royer oscillator type magnetic multivibrator. The multivibrator starts to oscillate by applying a ON signal pulse current (I_ON) to a coil set around the core, and stops oscillation by applying a OFF signal pulse current (I_OFF) to a small transistor which shorts another coil of the core. This module switched with the turn-on time t_ON of about 0.2µs and the turn-off time t_OFF of about 0.2µs when two switching transistors having a maximum rate of 1 A used. The values of t_ON and t_OFF is about 1/10 and 1/100 (due to the Meissner effect or zero inductance effect) that of the multivibrator transistor module using an amorphous ferromagnetic core. These transistor switch modules are applicable to construct high-speed inverters for the control of the small motors having high rotation speed.

We analyze current gain of the semiconductor-high T_c superconductor (HiTcSu)-semiconductor hot clectron transistor (HET) by taking into account quantum mechanical reflection (QMR) at the base-collector interface. Due to the small Fermi energy of HiTcSu, the QMR takes a minimum value when injected electrons pass just above the maximum of the collector barrier. With appropriate biasing voltage between base and collector, the QMR is found to be less than 0.05. The current gain is analyzed using the result of the QMR as function of base thickness, temperature, and the Fermi level of the emitter. With InAs and Si chosen as prototypes of semiconductors, the possibility to achieve current gain as large as 0.9 is indicated.

We have fabricated and measured step-edge microbridges of on-axis sputter-deposited YBCO films using the steps which exist on the cleaved surface of MgO substrate. The microbridges fabricated over the step behaved as Josephson devices, exhibiting clear Shapiro steps with microwave irradiation at 4.2 K. The critical current of the step-edge microbridge is one to two orders reduced from the critical current of the microbridge that has no steps within the same bridge region. The I_CR_N product is 0.5-1 mV with normal resistance of 1-4 Ω. The present technique utilizing the cleaved steps of MgO is useful for studying basic characteristics of the weak links with the step-edge structure.

We have fabricated all-Nb thin film microbridges by nanometer process using new resist developed by us, electron beam lithography (EBL) and reactive ion etching (RIE) using CBrF₃ gas. The resistance against CBrF₃ plasma of this EB resist is 4-10 times as strong as poly-(methyl methacrylate) PMMA. The merit of RIE using CBrF₃ gas is an anisotropic etching and high selectivity about resist and target. Trench of about 20 nm width was fabricated. Using this technique, the bridge with 40 nm length and 50 nm width was fabricated, and the thickness of bridge was 100 nm. The capacitance of the junction was estimated as 0.004 pF. Because of this small capacitance, fabricated samples are suitable for detection of submillimeter wave. The critical current I_c (T) of fabricated samples was proportional to (1T/T_c)^3/2 like variable thickness bridge (VTB). Moreover, Shapiro step up to the 11th under the millimeter wave radiation (70 GHz) was observed.

Rf properties of the coupling circuit between the dc SQUID and the multiturn input coil have been studied in order to investigate the origin of the degradation of the SQUID characteristics due to the input coil. It is pointed out that rf properties of the coupling circuit become important due to the existence of the rf currents generated from Jasephson junctions. The rf properties of the coupling circuit have been measured by using the expanded model of the circuit with Cu electrodes. We observe that resonant structures appear in rf properties of the coupling circuit. This means that the SQUID coil coupled to the input coil can not be expressed by a simple inductance, as is not the case of the isolated SQUID. It is shown that the resonant structures result from the standing wave occurring in the coupling circuit. It is also shown that the resonant structures can be suppressed with the damping resistors. Based on the experimental results, a circuit model of the coupling circuit is obtained, which explains well the experimental results. The obtained results are useful to study the effect of the input coil on SQUID characteristics.

We produced a double-layer thin-film heater to detrap magnetic flux in a SQUID sensor. The heater is integrated on a sensor chip, and consists of a lower resistor layer and an upper superconducting layer to cancel the magnetic field produced by the heater current. The SQUID sensor is cooled below its critical temperature with a temperature gradient to detrap the flux completely. To make the gradient, we had to decrease heater power to zero over an interval exceeding 10^-4 second in our experiment, which is almost equal to the sensor chip's thermal time constant. The integrated heater effectively controls the temperature profile and detraps flux in the sensor.

We have found a low frequency current oscillation in the n⁺-Al_xGa_1-xAs/GaAs (x0.4) modulation-doped electron systems under high electric field applied at low temperatures (77 K or lower). This paper gives a possible explanation for this on the basis of an enhanced Real-Space-Transfer (RST) of two-dimensional carriers caused by the field crowding at the local region along the heterointerface. This model explained the observed low frequency current oscillation semi-quantitatively.

Measurement results of two cascaded EDFAs (initial amplifier and boost amplifier) are reported for AM-FDM video distribution systems. A CNR of 55.5 dB and an output of 13.35 dBm (21.6mW) are measured. Distortion is measured by the two-tone method. On the basis of the measured distortion values, composite second-order distortion (CSO), composite triple beat distortion (CTB) and cross-modulation (XM) in a 40-channel transmission are estimated to be less than 56.9 dB, 66.3 dB and 74.6 dB, respectively. CNR values are strongly dependent on the erbium fiber length. They are degraded by light reflected from the input and output ports of the erbium fiber.

The low ohm metal film resistors under 1Ω can be made by electroless Ni-P plating. However, they are not suitable for precise use because their TCR can not become less than 100 ppm/. So the author developed Ni-W-P metal film resistors with its TCR is equal to conventional precision metal film resistors, by changing the ratio of ingredients in plating bath. At first on this paper, the trade-off point of ingredients ratio with respect to TCR and depositing rate has been investigated, assuming mass-production of 30,000 resistors in a lot. And then reliability tests, including short time over-load, temperature cycle, pulse, step stress, load life and moisture load life, were carried out for both conventional Ni-P and Ni-W-P metal film resistors. Before the tests, the films were grooved by laser and mechanical cutting. As the result, it has been found that the Ni-W-P is superior to the Ni-P, especially in step stress and pulse, and that laser cutting is found preferable to mechanical cutting.

A current continuity equation is proposed as the additional equation for the GTD-MM hybrid technique formulation to acquire the uniqueness of the solution which were nonexistent in the conventional formulation with the matching-point equation. The current continuity equation, which ensures the current continuity and satisfies the boundary condition, can directly be written down through equating the MM-region current to the GTD-region current at the regions boundary. It is proved that the current continuity equation is equivalent to the matching-point equation of special case when the matching-point located very close to the boundary, which were able to give the best solution in the conventional formulation with the matching-point equation as explained by Burnside et al. The validity of the new equation is confirmed through the numerical results.