The barrier-layer was successfully fabricated for a preparation of tunneling junction using high T_c oxidesuperconductor such as Bi-Sr-Ca-Cu-O system. Bi₂Sr₂Ca₂Cu₃O_x 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.

A sputtering system using dc hollow cathode discharge was developed for the propose of high T_c superconducting devices. Using this system, as-grown superconducting thin films of YBCO have been formed on MgO and SrTiO₃ substrates. Influence of the sputtering conditions such as the substrate temperature and discharge gas pressure on the T_c and lattice parameter was investigated. It was found that superconducting films on MgO with T_c・zero higher than 87 K ere routinely obtained at the pressure of 820 mTorr (5%O₂) and substrate temperature of 700 during deposition. The a/b-axis and c-axis oriented YBCO-PBCO hetero-structures were also successfully formed on MgO and SrTiO₃ substrates.

Amorphous films of YBCO and BSCCO (2212) sputtered on MgO substrate were crystallized using zonemelt technique. For YBCO films, thin Ag intermediate layer was found to be effective in enhancing crystal growth and preferred orientation. Zone-melted BSCCO films included both (2201) phase and Cu(Sr, Ca)O₂ in a form of dendritic crystallites. T_c's obtained for YBCO and BSCCO films were 70 and 75 K, respectively.

Bi₂Sr₂CuO_x (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.

The (100) oriented Ba_xRb_1-xBiO₃ (BRBO) thin films were prepared on MgO (100) and SrTiO₃(100) (STO(100)) substrate by molecular beam epitaxy using distilled ozone. The (100)-oriented BRBO thin film deposited on STO(100) substrate, showed onset superconducting transition temperature (T_c(onset)) value of 28 K and zero-resistance superconducting transition temperature (T_c(0)) value of 26 K. The respective values for T_c(onset) and T_c(0) of BRBO thin film on MgO(100) substrate were 21 K and 19 K. The growth process of the BRBO thin films grown on MgO(100) and STO(100) substrates were studied by the atomic force microscope (AFM) and the X-ray photoelectron spectroscopy (XPS). Difference in XPS-intensity of Ba as a function of the average thickness for the BRBO thin films deposited on STO(100) substrate and on MgO(100) substrate were observed. The electrical properties of junction using the BRBO thin film and the Nb-doped STO substrate (BRBO/STO(Nb)) was also investigated. The results of the current-voltage measurement and the capacitance-voltage measurement revealed that it is not necessary to take into account the unknown dielectric layer at the interface of BRBO/STO (Nb). It was not possible to interpret well the resistance-temperature behavior of Rb-doped-BaBiO₃ thin film (semiconducting BBO(Rb) thin film) with the help of hopping model.

Structure and resistivity of BaBiO_y were compared with those of Ba_1-xLa_xBiO₃. Decrease in an average Bi valence from 3.91 to 3.03 for BaBiO_y leads to an increase in the lattice parameter c from 4.37 to 4.53 , in the unit cell volume from 81 ³ to 87 ³, and in the resistivity from 10 Ωcm to 210⁵ Ωcm. It was found that the increase in the unit cell volume and the resistivity was due to change in the average Bi valence. The resistivity of BaBi_1-xLa_xO₃ was compared with that of BaBiO_y and Ba_1-xLa_xBiO₃. We also found that pseudocubic Ba_1-xLa_xBiO₃ remains semiconducting as well as pseudotetragonal BaBiO_y. The high resistivity in the Ba_1-xLa_xBiO₃ and the BaBi_1-xLa_xO₃ will be useful to the application for the SIS junction.

We have fabricated bi-epitaxial grain boundary junctions in YBa₂Cu₃O_7δ (YBCO) thin films by using SrTiO₃ (STO) seed layers on MgO(100) substrate. YBCO film growing over the STO seed layer has a different in-plane orientation from YBCO film without the seed layer, so artificial grain boundaries were created at the edge of the seed layer. The fabricated junctions have high T_c (up to 80 K), and constant-voltage current steps are observed in response to 12.1 GHz microwave radiation. Moreover, some of the junctions show characteristic current-voltage curves comprising not only an usual Josephson-like characteristic but also a low critical current due to the flux creep. This suggests that the two characteristic parts are likely to be connected in series at the junction region.

A YBCO/CeO₂/Au MIS structure (YBCO:YBa₂Cu₃O_7y) 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.

In order to explain the temperature and frequency characteristics of high-T_c 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 Z_sR_sjX_s, where R_s is the surface resistance and X_s is the surface reactance, are expressed as a function of temperature. The temperature dependences of Z_s 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 T_c 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-T_c superconductors in room to cryogenic temperature. On the other hand, the residual normal electron density n_res4.25410²³ m^-3 and the total electron density n_t7.30810²⁴ m^-3 are obtained by calculation. The ratio n_res/n_t0.058 can be used as figure of merit to evaluate material quality of high-T_c superconductors; thus it means that there is 5.8% nonpairing electron in this YBCO bulk.

Bi₂Sr₂Ca₁Cu₂O_x 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.

Microwave characteristics of a LiNbO₃ optical modulator employing superconductor electrodes (Pb-In-Au) as a transmission line of a traveling signal has been studied experimentally in the temperature range from 300 K to 4.2 K. At frequencies between 8 GHz and 12 GHz it is shown that the obtained modulation efficiency increases as expected from theory when the superconductor undergoes the transition from a normal state to a superconducting state. The present results dumonstrate the possible applications of superconducting electrodes to high performance LiNbO₃ optical modulators.

The threshold characteristics of mutually coupled SQUIDs (Superconducting Quantum Interference Devices) have been analytically and numerically investigated. The mutually coupled SQUIDs investigated is composed of an rf-SQUID and a dc-SQUID. Here, the rf-SQUID is a flux quantum generator and the dc-SQUID is a flux detector. The linearization method substituting sin^-1x by (π/2)x (1x1) is found valid when it is applied to the mutually coupled SQUIDs, because it is possible to obtain the superconducting regions analytically. By computer implementation of linearization method, we found this method is very effective and very quick compared to the ordinary methods. We report the internal flux on an rf-SQUID, the threshold of a dc-SQUID, and that of mutually coupled SQUIDs obtained by Lagrange multiplier formulation and linearization. The features of the threshold characteristics of the mutually coupled SQUIDs with various parameters are also reported. The discontinuous behavior of threshold of the mutually coupled SQUIDs are attractive for digital applications. We suggest three applications of the mutually coupled SQUIDs, that is, a logic gate for high-T_c superconductors (HTSs), a neuron device, and an A/D converter.

Nojima and Fujita have found a universal relation, irrespective of temperatures T, between the reduced field hH/H_ir(T) and the reduced quantity of magnetization hysteresis mΔM (T, H)/ΔM (T, H0), where H_ir is the irreversibility field and ΔM(T, H) is the hysteresis of magnetization for YBa₂Cu₃O_x and Bi₂Sr₂CaCu₂O_x films. We could explain this universal relation based on a scaling theory in a three-dimensional superconducting vortex-glass phase. The exponent ν derived by this relation coincides with that obtained by nonlinear I-V characteristics for YBa₂Cu₃O_x films.

In order to investigate the characteristics of the superconducting gap structures of BSCCO oxide superconductor, tunneling spectrum measurements were carried out with several junctions on the bulk single crystal surfaces. Point contact tunneling studies by means of the M/I/S and S/(I)/S junctions have shown the reproducible gap values, 2Δ (//c-axis) of 402 meV, at the cleaved crystal surfaces, and the ratio of 2Δ(//)/k_BT_c5.50.3 indicates the strong coupling superconductor of this material. Somewhat larger gap values, 2Δ_max(c-axis)701 meV, have been also observed at the lateral surface, and these various gap values observed on each surface of the same crystal indicate the characteristic of the large gap anisotropy, Δ()/Δ(//)1.8, of this material.

The Cooper pairing interaction in high T_c oxide superconductor is discussed in terms of an empirical expression; T_cDexp[1/g], gc・ω_o which was derived in our previous investigation. The dual character of this expression consisting of the phonon Debye temperature _D and electronic excitation ω_o 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.

Experimental results of an N-S junction and analysis of the results using the Arnold theory were reported. Au and Pb were employed as a normal metal and a superconducting material, respectively. The excess current effect due to the Andreev reflection was observed in the current-voltage characteristics of an N-S junction whose normal resistance was 1.603 Ω. The excess current at 4.62 K was about 0.7 mA when the applied voltage was 2 mV. The barrier height and width were estimated to be 1.0169 eV and 0.7 , respectively, by comparing the experimental results and analysis based on the Arnold theory. In the voltage region less than 2 mV, the theory well agreed with the experiment. Moreover, the applied voltage dependence of the supercurrent and quasiparticle current were separately calculated. It was made clear that the supercurrent was larger than the quasiparticle current in the voltage region less than 2Δ/e, where Δ is the superconducting energy gap and e is the absolute value of an electron's charge. The supercurrent began to gradually saturate when the voltage was higher than Δ/e and became constant at the applied voltage greater than 2Δ/e. In our experiment, the excess current larger than expected from the Arnold theory was observed in the voltage region higher than 2Δ/e.

This paper describes the dependence of the delay time of a CMOS/SIMOX inverter on the gate-overlap capacitance. An analytical delay-time equation for the CMOS/SIMOX inverter, which includes the gate-overlap capacitance, is derived. This equation shows that the feed-forward effect dominates the characteristics of inverters with a small fanout. The validity of the delay-time equation is confirmed by the comparison to experimental measurements of 0.4-µm CMOS/SIMOX devices. Moreover, a sensitivity analysis shows that it is very important to reduce the gate-drain overlap capacitance for fabricating high-speed scaled-down CMOS/SIMOX devices.

The beam propagation method (BPM) is a powerful and manageable method for the analysis of wave propagation along weakly guiding optical waveguides. However, the effects of reflected waves are not considered in the original BPM. In this paper, we propose two simple modifications of the BPM to make it relevant in characterizing waveguide discontinuities at which a significant amount of reflection is expected to be observed. Validity of the present modifications is confirmed by the numerical results for the slab waveguide discontinuities and the butt-joints between different slab waveguides which either support the dominant mode or higher order modes.

Properties of a strongly-coupled nonlinear directional coupler (NLDC) with a lossy MQW coupling layer is analyzed using the Galerkin finite element method accompanied by a predictor-corrector algorithm. It is shown that the propagation attenuation along the NLDC is considerably smaller than that in the bulk MQW and tends to reduce with the input power. By the presence of losses, the powers guided in two waveguides do not become a maximum and a minimum at the same propagation length, unlike the lossless coupler. The losses make the nonlinear effect weak due to the decrease in guided power, and hence the coupling length decreases and the switching power increases. The extinction ratio of the switching becomes the largest value not in the cases of nonloss and high losses but in the case of moderately high losses, although the switching power is somewhat larger than that of the lossless case.

Power transmission properties are investigated for a butt-joint which contains an air gap between an isotropic planar waveguide and an anisotropic one whose optical axis is lying in the plane defined by the propagation axis and the normal of the waveguide surface. New transmission coefficients are introduced for estimating the optical-power which is launched out into the gap from the incoming waveguide. Wave propagation through the gap is analyzed on the basis of the BPM concept. And the power transmitted across the interface between the gap and the outgoing waveguide is evaluated by means of the overlap integral of the field profiles. The effects of the air gap and the refractive index of filling liquid as well as axial displacement and angular misalignment are discussed on the basis of numerical results.