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Measurement methods with SQUID can accurately detect small magnetic metal contaminants based on their magnetic remanence. But, a high-frequency excitation is necessary to detect nonmagnetic metals, on the base of contrasts in electric conductivity. In this work, an open loop technique is introduced to facilitate this. The SQUID is negative feedback controlled (flux locked loop (FLL) operation) for the low frequency range, which includes significant noise due to the movement of the magnetic body or the change of the ambient magnetic field composed of the geomagnetic field and technical signals, and it operates in an open loop configuration for the high frequency range. When using the open loop technique, negative feedback is not applied to the high frequency range. Consequently, the V–Φ characteristic changes due to various causes, which leads to variations in the conversion factor between the SQUID output voltage and the magnetic field. In this study, conversion techniques for the magnetic field for open loop operation of SQUID in the high frequency range are examined.

When performing high-sensitivity magnetic measurements via a high-sensitivity magnetic sensor such as a SQUID (Superconducting QUantum Interference Device) magnetometer, it is necessary to shield from environmental magnetic noise by employing a magnetic shield box. In general, however, the low frequency of such noise decreases the shielding performance of the magnetic shield box. Hence, the magnetic metallic contaminant signal and the low-frequency ambient magnetic field noise overlap, which makes filtering a challenging task. Therefore, we studied a system that suppresses gradient magnetic noise such as low-frequency environmental noise superimposed on a contaminant signal and commercial power supply noise localized spatially.

In a conventional transformer, secondary voltage and power transfer efficiency decrease when the magnetic flux leaks from the magnetic circuit of the transformer and the leakage reactance increases. Magnetic shielding of the magnetic circuit of the transformer with plural bulk high temperature superconductors (HTSs) was evaluated as a method of improving transformer characteristics. In our previous research, transformer characteristics were evaluated with a constant secondary load at each frequency. In this research, appropriate secondary loads were connected for each frequency to evaluate the characteristics in conformity with the actual transformer operation. The frequency characteristics of transformers with and without bulk HTSs shielding were evaluated with a constant magnetic flux density in the magnetic circuit. An increase in the secondary voltage and power transfer efficiency was confirmed for a transformer with bulk HTSs shielding at all frequencies, as dispersion of the magnetic flux was controlled by bulk HTSs shielding.

Magnetocardiographic (MCG) measurement in unshielded environment for practical use requires to suppress the environmental magnetic noise. We have designed the high critical temperature superconducting quantum interference device (High- T c SQUID) magnetometer with feedforward active noise control (ANC) system to suppress the environmental magnetic noise. The compensatory system consisted of two SQUID magnetometers, a digital signal processor (DSP) and the coil wound around the input magnetometer. The DSP calculated the output data to minimize the environmental noise from the input and reference date and then the coil generated the magnetic field to cancel the environmental noise. This method achieved the effective noise attenuation below 100 Hz about 40 dB. MCG measurement in unshielded environment was also performed.

The authors systematically investigated the effects of discharge gas pressure on in situ YBaCuO thin-film formation by RF magnetron sputtering and ensured the reliability of the epitaxial YBaCuO films by pressure control. The film (100-nm thick and no protection) showed no sign of degradation in its T/sub c/ value for approximately 3000 h. Under the controlled discharge gas pressure, the in situ epitaxial YBaCuO film had a T/sub c/ of 87 K. The c-axis lattice constants and the critical temperatures came very close to the bulk values as the pressure was rising to 1 torr. The plasma emission spectra showed a reduction in the Ar spectrum intensities relative to the oxygen component with increasing pressure. This observation suggests that the reduced mean free path of the gas atoms is responsible for the improved film crystallinity and superconductivity.

The hole-carrier transport in the epitaxial (001) Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub y} thin films has been closely investigated under the application of pulsed high electric field. In every current-electric field curve of the normal conduction, strong nonlinearity appeared: currents no longer increased as the electric field increased in excess of certain threshold values. Observed current saturation was much more exaggerated with increasing low-field mobility (at lower temperatures or better quality films). These new phenomena of the high temperature superconductors are very similar to the hot-carrier transport well-known in the semiconducting materials. In the paper, comparisons concerning the threshold field intensity, electron temperatures and so on between the oxide superconductors and the typical semiconductors.

The feasibility of the selective (001)Y I Baz Cu3 0 epitaxy have been closely examined. We have obtained the selective growth of epilaxial Y 1 Baa CUJ 0 and heteroepitaxial (100)MgO/(001)- Y1 Baz Cu3 0 layers through the Si0 window. The MOS-capacitors and MOS-FETs were fabricated in the same way.

Homoepitaxy of the diamond thin films has been carried out by employing the ECR microwave plasma CVD apparatus with a CO/H2 gaseous source. From RHEED observation, it appeared that the surface morphology of (100) oriented film was much better than that of the (110) oriented. The (2×1) surface reconstruction remained unchanged even when the film was cooled down in H2 ambient after the epitaxy was completed. Although the synthetic diamond substrates had nonuniformity in their cathodoluminescence patterns, epitaxial films grown onto them offered uniform ones.

The significant current saturation against the 20‐ns‐wide pulsed electric field above the threshold value E th (∼2 kV/cm) was observed in the semiconducting phase YBa2Cu3O y epitaxialfilms at low temperatures. Although E th increased up to 3–7 kV/cm, the superconducting phase films also showed the same nonlinearity in their normal conduction at low temperatures. The value of E th lowered with reducing temperature where the carrier concentration and mobility decreased and increased, respectively. These characteristic features are explained by the well‐known hot‐carrier effect in the familiar semiconducting materials.

The oxide high temperature superconductors (HTSC) have characteristic features in common such as a very short coherence length even in the Cu-O2 plane, compound crystals with multi-element, large anisotropies in their crystal structure and superconductivity, and fugacity of the constituent atoms. All those are difficulties we face at least at present in applying HTSCs to the electronics field. Particularly, both the short coherence length and atomic fugacity are thought as the major causes of missing superconductivity at the surface and/or interface. To overcome those difficulties, we proposed an introduction of heteroepitaxial growth technologies into HTSCs and so far we successfully obtained the doubleheteroepitaxial structures like (001)YBCO/(100)MgO/(100)YBC0, (110)YBCO/ (~100)Mg0/(110)YBCO and (001)YBCO/(100)Mg0/(001)YBCO.1-3) Those epitaxial structures are indispensable for the tunneling SIS Josephson junction and future devices like SUPER-HET and Field Effect Transistors.

We have fabricated the YBaCuO/MgO/YBaCuO double-heterostructure using conventional rf-magnetron sputtering. The formation of both (110)YBaCuO/(100)MgO/ (110)YBaCuO on (110)SrTiO3 substrate, and (001)YBaCuO/(100)MgO/(100)YBaCuO and (001)YBaCuO/(100)MgO/(001)YBaCuO on (100)MgO substrate, became feasible. According to the RHEED observations, each layer of the double-heterostructure was grown epitaxially. The cross sectional TEM observation was carried out for characterizations of the heterostructure, bringing a number of informations concerning the interfacial problems. Final discussion is on the electric field effect of Al/MgO/YBaCuO, as a new application of the heterostructure.

Generalized harmonic analysis was applied to a high-temperature superconducting quantum interference device (SQUID) magnetocardiograph signal processing system. The noise frequencies in the signal waveform were calculated by the generalized harmonic analysis (GHA) and the noise components with these frequencies were subtracted from the acquired signal data. Two types of the subtraction procedure were demonstrated: one using the adaptive filtering algorithm and the other a simple subtraction. In both cases, the noise components were reduced. The former system performed rapid calculations but generated an artificial noise in the high-frequency region, because of rough GHA estimation, while in the latter case, the calculation was time-consuming but the noise estimation was carried out accurately, because of the precision of GHA procedure. In the present study, a distinctive noise component at 16 Hz was completely suppressed by the GHA prediction noise reduction process. The proposed systems were well suited for application to an unshielded high-temperature SQUID system.

The surface morphology of both YBa2Cu3O y (YBCO) thin film on a MgO substrate and SrTiO3 (STO) thin film on a YBCO film was observed using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) methods. These films were deposited by the ArF excimer laser deposition method. The c-axis-oriented YBCO film of 100 nm thickness grew spirally on a (100)MgO substrate in an island growth mode. The heteroepitaxial STO thin film deposited in situ on the YBCO film grew as if they had filled in the steps of the spiral structure of the YBCO thin film at the stage of initial growth, i.e., STO grew in a kink growth mode. The LEED pattern indicates that the film surface coverd with STO was stable against ordinary air, although the thickness of STO thin film was about 1 nm.

The electric field effect in YBa2Cu3O y (YBCO) thin film was investigated by means of drain-current modulation measurements on Al/(100)SrTiO3/(001)YBCO metal-insulator-superconductor field-effect transistors (MISFETs) in the normal state. Sufficient current modulation was obtained in every specimen without exception. Moreover, even an YBCO channel with a semi-insulating phase could be changed to a conductive state by the field effect. The semiconductor band model explained the observed electric field effect semi-quantitatively.

Hydrogenation of diamond has been carried out using the electron-cyclotron-resonance microwave plasma chemical-vapor deposition apparatus. According to reflection high-energy and low-energy electron diffraction and X-ray photoelectron spectroscopy measurements, the natural- and synthetic-diamond surfaces maintained their crystallinity even after the hydrogenation. Seebeck effect measurement and the temperature dependence of the resistance revealed an appearance of deep acceptor levels in the hydrogenated diamond layer. The diffusion depth of the hydrogen by the plasma treatment (2 h, 830°C) was roughly estimated to be ∼0.6 µm from the drain current-voltage characteristics of a rudimentary MISFET using the hydrogenated diamond.

The dielectric properties of SrTiO3 epitaxial film were studied using film grown on oxide superconductor YBa2Cu3O y . They were, to a certain extent, similar to those of the single-crystal bulk in terms of both temperature and electric field dependence, though the value of the dielectric constant was low, particularly at cryogenic temperatures. The observed dielectric properties were analytically expressed. Using the dramatic field dependence of the dielectric constant of the SrTiO3 film in the Au-SrTiO3-YBa2Cu3O y metal-insulator-superconductor (MIS) structure, we determined the work function of (001)YBa2Cu3O y epitaxial film to be ∼6.1 eV.

Planar-type Al/(100)SrTiO3/(001)YBa2Cu3O y metal-insulator-superconductor field-effect transistors (MISFETs) were investigated experimentally and theoretically. The applied gate field induces the change of the carrier concentration in YBa2Cu3O y channel (or conducting layer thickness), which in turn modulates the critical current J c through the flux-creep model and flux-flow resistivity ρt through the Bardeen-Stephen model. Theoretical results explained, to a certain extent, the observed field effect in the MISFET semiquantitatively.

The oxygen annealing (OA) effects on MgO substrates commercially available were closely investigated. The smeared low-energy electron diffraction spot pattern and transmissionlike spot pattern of reflection high-energy electron diffraction were dramatically changed to those of almost ideal MgO crystals through OA at 1000°C. After OA, the spotty cathodeluminescence (CL) pattern disappeared almost completely, and the peak wave-length of CL spectra shifted from blue (∼400 nm) to red (∼715 nm). The 5-nm-thick epitaxial YBaCuO films grown on (100)MgO substrates with OA exhibited good superconductivity. Otherwise, superconductivity was not evident. However, the macroscopic subgrain structure seen in the X-ray topographs showed no meaningful changes between before and after OA.

Planar-type metal-insulator-superconductor field-effect-transistors (MISFET) were fabricated and their current modulation characteristics were investigated. The FET had a structure of Al-gate metal/(100)SrTiO3-gate insulator/(001)YBa2Cu3O y -channel, where the oxide layers were grown by selective heteroepitaxy employing pulsed ArF excimer laser deposition. The FET gate was 10 µm long and 100 µm wide. Apparent field-effect modulation of drain current was seen in both the normal (T>T c) and superconducting (T

SrTiO3 (STO) thin films were prepared by an ArF excimer laser deposition method. At the growth temperature of 630°C, the natural orientation of STO was significantly changed from (111) to (100) and (110). The ratio of X-ray diffraction intensities (100)/(200) was closest to the ideal value when grown at 660°C, resulting in minimized disorder of atomic arrangement. Epitaxial STO films were obtained on STO(100) and MgO(100) substrates, and on an YBaCuO(001) epitaxial film. They showed resistivity in excess of 5×1010 Ω·cm and dielectric constant as high as 140ε0 at room temperature. The maximum dielectric constant of 440ε0 was obtained at 40 K.

Oxide superconducting YBaCuO thin films were grown on Y- and Z-cut LiNbO3 (LN) electrooptic crystal substrates with and without buffer layers, and their film crystallinity was closely investigated by X-ray diffraction, transmission electron microscopy, reflection high-energy electron diffraction and Auger electron spectroscopy. Due to the intensive reaction, direct deposition of films resulted in poor quality. When sputtered (111)-MgO film was introduced as a buffer layer, significant diffusion of constituent atoms was unavoidable among YBaCuO, MgO and LN. As a result, the superconductivity of the YBaCuO layer was substantially degraded. The Y2O3- stabilized ZrO2 (YSZ) grown by sputtering, followed by wet O2 anneal, served as a good buffer layer for Y1Ba2Cu3O y films on LN substrates, and epitaxial growth of (00l)-Y1Ba2Cu3O y with T c0=89 K was reproducibly obtained on Y-cut LN substrates.

Hot carrier transport in epitaxial (001)Y1Ba2Cu3O y thin films has been closely investigated under application of pulsed high electric field. The current-vs-field curves of the normal conduction for both the semiconducting and superconducting phase films exhibited strong nonlinearity as the field increased. The nonlinearity of the dynamic resistance measured at 50-100 MHz was exaggerated much more. These phenomena were analyzed through analogy to the high-field transport in semiconductors. On the basis of the dominant phonon scattering, the results implied that the Y1Ba2Cu3O y carrier localizes in a thin layer and has two-dimensional motion, and that the deduced effective mass is heavier than 2m 0 but less than 5m 0, where m 0 is the free electron mass.

The effects of gas exposure on the clean surface of the epitaxial YBaCuO thin films were closely investigated using the low-energy electron diffraction (LEED) method. The clean surface was obtained by in-vacuum annealing at 500°C. Once the clean surface was exposed to air, even at room temperature, the LEED spots disappeared or sometimes became faint. To ensure the degradation mechanism of the YBaCuO clean surface, the specimens were exposed to pure O2 and N2 gases separately and measured by LEED. As a result, it was found that O2 is very safe but N2 serves as a poisonous gas for the YBaCuO clean surface.

The surface structure of 80 K-phase BiSrCaCuO single crystals with and without Li doping has been studied using low-energy electron diffraction (LEED) at elevated temperatures. Although the superconducting critical temperature rises slightly with Li doping, the cleaved surface becomes amorphous in vacuum at temperature ∼100 degrees lower than that of the undoped sample (600°C).

Diamond thin films have been grown by an electron-cyclotron-resonance (ECR) microwave plasma chemical vapor deposition (CVD) apparatus under the addition of oxygen to the host ambient gas of a mixture of CO and H2 gas. Although the amount of oxygen was very minute (0-6% vol. fraction), significant changes due to the oxygen were brought about in the growth properties and the film crystallinity. The Raman spectroscopy revealed a dramatically improved film crystallinity and the film was dominated by the grain growth, resulting in the faceted morphology. With increase in the oxygen up to 4.55%, the visible cathodeluminescence (CL) intensity grew by more than ten times. However, the CL spectrum indicated an appearance of one or two extra recombination centers depending on the amount of oxygen.

The selective Y1Ba2Cu3O y epitaxial growth and, as its advanced technology, MgO/Y1Ba2Cu3O y selective heteroepitaxy are demonstrated. The film growth was done by the pressure-controlled magnetron sputtering on the MgO substrate with partial SiO coating. The epitaxial Y1Ba2Cu3O y films were grown in the patterned shape through a SiO window, showing the critical temperature of 77 K. In the remaining wafer region where the film contacted the underlying SiO, significant Si and Ba interdiffusion was found, resulting in the amorphous and insulating Y-Ba-Cu-Si-O. In the same way, the selective heteroepitaxy was also successfully obtained.

The in situ epitaxial growth of the YBaCuO film was carried out by the reactive magnetron sputtering under discharging gas pressures ranging from 4–120 Pa. It appeared that the pressure strongly affected not only the deviation of the film composition from the target but also the film crystallinity which is in turn closely correlated to the superconductivity and its stability. In the plasma emission spectra, we found a reduction in the Ar spectrum intensities relative to those of the metal components with increasing pressure.

This letter describes the first observation of catastrophic local degradation of epitaxially grown YBa2Cu3O y film due to pulsed high electric field application in the normal conduction state. In the degraded samples, a damaged region like a crack appears which was not seen in the sound stage. Cathodoluminescence image observation, which reflects the distribution of defects inside MgO substrates, suggested that the local degradation of YBa2Cu3O y film occurred where defects in the substrate materials were aggregated.

Effects of hydrogen trapping in Nb base electrodes on the superconductivity of Nb itself and superconductor‐insulator‐superconductor (SIS) junction characteristics have been investigated. The Nb films were prepared by sputter deposition in an atmosphere of (Ar, H2) mixture. The gap parameter ΔNb and the critical temperature Tc gradually decreased with increasing H2 partial pressure. The SIS junctions exhibited a sudden extinction of the Josephson current Ic when ΔNb was lowered to or less than 1.1 meV by H2 trapping. Such a junction could be used as a quasiparticle tunneling junction for microwave detection with no requirement for an external magnetic field.