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The response of microwave impedance in a highly c -axis oriented EuBa 2 Cu 3 O 7− x film to a low DC magnetic field ( H 2 dependence, as predicted by the G–L model for pair-breaking in the Meissner state. However, clear saturation was observed in the surface impedance response with the field normal to the surface. Therefore, these responses were thought to arise from the properties of the weak links remaining in the film.

It is expected that the superior high-frequency characteristics, such as low loss and low dispersion, of superconducting oxides are applied to microwave circuits. However, low-loss superconducting oxide films can only be fabricated on limited types of substrate materials using present technologies. Therefore, the dielectric constant, dielectric loss, and thickness of substrate materials place severe limitations on the circuit design and the propagation characteristics. This paper discusses the attenuation constants, characteristic impedances, and wiring density of three fundamental planar transmission lines, namely, stripline, microstrip line, and coplanar waveguide fabricated on substrate materials MgO and LaAlO3. This discussion is based on the TEM and quasi-TEM analysis procedures. The thin films with low surface resistances have been fabricated on MgO and LaAlO3. It is concluded that the microstrip line is suitable for fabricating a low-loss transmission line and the coplanar waveguide on a low dielectric constant substrate is suitable for high-density wirings. Also measured were the characteristics of the half-wave transmission line resonators of these three transmission line configurations, which are made of EuBa2Cu3Ox thin films on an MgO substrate. The attenuation constant of 50 Ω, 50-μm wide coplanar waveguide is 9.7 × 10−3 Np/m (8.4 × 10−2 dB/m) at 3.9 GHz and 28 K. This value is two orders of magnitude lower than that of the copper transmission line.

We measure the relative permittivitye r and dielectric loss tangent tanδ of substrate materials for high-T c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. Thee r values are 10–30 and become almost constant below about 50 K. The tanδ values decrease with decreasing temperature and are below 1×10−5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tanδ values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T c superconducting films. It is also demonstrated that the tanδ of the substrate material is strongly affected by impurities.

Superconducting thin films of YBa 2 Cu 3 O 7−y were prepared by ECR sputtering. The amorphous films obtained at relatively low substrate temperatures (up to 400°C) were annealed in an oxygen flow. The Tc of the annealed film was 90 K and showed high c-axis orientation. The change of 124 phase to 123 phase was observed by changing annealing temperature

We have measured the microwave surface resistance of sputtered EuBa2Cu3O7−x superconducting films on MgO in a gold‐plated Invar host cavity at 50 GHz. Low surface resistance of 2 mΩ was achieved even at 77 K and 50 GHz for highly c‐axis oriented films with good in‐plane epitaxy together with a Tc of 93 K and a Jc of 1.4×106 A/cm2 at 90 K. This surface resistance value is slightly lower than that for a classical superconductor of Nb at the same frequency at the same reduced temperature (T/Tc) of 7.7 K.

We report the reduction of particulates on YBa 2 Cu 3 O x thin films. The origin of particulates is investigated from the viewpoint of particulate generation on targets. Films were prepared by means of pulsed ArF excimer laser (193nm) deposition. The irradiated part of the YBa 2 Cu 3 O x ceramic target was observed to be melted during irradiation by scanning electron microscopy (SEM). We believe that one of the main origin of particulates is the splashing of molten YBa 2 Cu 3 O x particles. The melting were thought to be due to the poor thermal conductivity of the ceramic target. To increase thermal conductivity, we used an YBa 2 Cu 3 O x crystalline target extracted from a MPMG grown polycrystal. In addition, a small shielding plate was inserted between the target and the substrate to avoid direct arrival of molten particulates from the target. Low particulate density YBa 2 Cu 3 O x thin films (~ 10 3 /cm 2 ) were reproducibly obtained by using the crystal target and the shielding plate.

The surface resistance of high-Tc superconducting c-axis oriented EuBa2Cu3Ox thin film sputtered on MgO is greatly lowered by reducing in-plane misorientation. A coplanar delay line with the delay time of 6.1 nsec and a insertion loss of 0.03 dB/nsec at 77 K and 1 GHz are fabricated using the EuBa2Cu3Ox thin film. We summarize recently reported data on high-Tc superconducting resonators, bandpass filters and delay lines.

Microwave surface resistance induced by a low magnetic field in HTSC thin film is measured using a coplanar line resonator. The directional dependence of field induced surface resistance is observed. To understand this directional dependence, it is useful to introduce the concept of intergrain flux-flow resistance.

This paper describes the influence of amorphous fluoropolymer (AF) film on the properties of high-T c superconductive microwave components, when it is used for surface protection and as a spacer. It is found that AF film can protect EuBaCuO and TlBaCaCuO superconducting film from dampness, thus maintaining the properties of a microstrip resonator for at least 1000 h. The AF protection has almost no effect on properties such as temperature dependence and unloaded-Q values in high-Q microwave components. Additionally, the use of AF film as a spacer in a strip-line structure reduces the influence of spacing on the effective dielectric constant and characteristic impedance.

This letter describes the surface resistance of YBa2Cu3O7-x thick films which are screen printed on Ag-coated Y2O3-stabilized ZrO2 substrates. The surface resistance decreases with decreasing YBa2Cu3O7-x film thickness. The 7 µm-thick film shows the lowest surface resistances (8.2 m Ω at 17 GHz and 48 m Ω at 50 GHz at liquid nitrogen temperature) which are lower than those of pure Cu. These markedly low surface resistances are attributed to the enhanced growth and c-axis orientation of YBa2Cu3O7-x grains.

Epitaxial growth of 1-2-3 superconductor films is reported on a new substrate material that possesses desirable dielectric properties. Magnetron-sputtered EuBa2Cu3O7-y films on YAlO3(001) show excellent properties with a T c of 91 K. Films are epitaxially grown with the c-axis oriented normal to the surface, and the a- and b-axes ordered in the plane. The high-frequency (50 GHz) surface resistance of a film is 2 mΩ at 30 K. The dielectric constant of YAlO3 is 16. The dielectric loss tangent at 10 GHz is as low as 7.3×10-5 at 300 K and 2×10-6 at 40 K. YAlO3-based films have considerable potential for high-frequency application.

This letter describes the effect of Ag addition on the surface resistance of sintered YBa2Cu3O7-x superconductors at 17 and 50 GHz. The surface resistance decreases more than 50% by adding Ag into a pellet or a thick film of YBa2Cu3O7-x . The thick film exhibits a surface resistance of 22 mΩ at 17 GHz and at 77 K, which is almost equal to that of pure Cu. It is also revealed that the surface resistance is proportional to the square of the frequency. These phenomena are discussed in terms of the effect of Ag on the morphologies and c-axis orientation of YBa2Cu3O7-x grains.

We have measured the surface resistance of c-axis-oriented EuBa2Cu3O7-y thin films grown in situ onto (100)MgO by magnetron sputtering. The measurements were made at 50 GHz between 20 and 300 K in a TE013 gold-plated invar cavity by replacing the endplate with a film. The surface resistance decreases sharply at 87 K to 40 m Ω at 77 K, becomes lower than that of an OFHC copper plate below 74 K, and lies within the measurement sensitivity range of 2 m Ω below 60 K. This low surface resistance suggests that MgO-based films are very suitable for high-frequency applications.

Y-Ba-Cu-O superconducting tapes over 10 m long were produced by an atmospheric plasma spraying method. After annealing at 900°C in an oxygen flow Tc (onset) and Tc (zero resistance) were 94K and 88K, respectively. Jc at liquid nitrogen temperature was about 6 A/cm2 in the length range of 7.8 m. Increasing the substrate temperature decreased the post-annealing temperature necessary to obtain superconductivity. As-sprayed film on 900°C substrate showed 80 K superconductivity. The (Bi/Pb)—Sr—Ca—Cu—O superconducting films with high Tc (110 K) and low Tc (80 K) phases were prepared and the superconductivity was affected by the Pb content and the oxygen pressure in the postannealing atmosphere.

The magnetic-field dependence of the microwave surface resistance of both single crystals and sintered crystals of YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) has been measured at 24 GHz. The resistance decreases below the superconducting transition temperature and reaches a constant residual resistance. The value is much lower for single crystals than for polycrystals. Furthermore, polycrystals showed magnetoresistance at low field and magnetoresistance with hysteresis at high field, which resembles the magnetization behavior of typical type-II superconductors. The observed magnetoresistance is shown to be inherent to a sintered polycrystal which is composed of grains and contains many voids. The single crystal showed lower magnetoresistance. >

The magnetic field dependence of microwave surface resistance of both single crystals and sintered polycrystals of YBa2Cu3O7-δ has been measured at 24 GHz. The resistance decreases below superconducting transition temperature and reaches constant residual resistance. The value is much lower for single crystals than for polycrystals. Furthermore polycrystals showed low field magnetoresistance and high field one with hysteresis which resembles the magnetization behavior of typical type II superconductor. The single crystal, however, showed nearly no magnetoresistance. The magnetoresistance observed is proved to be a inherent phenomena to sintered polycrystal which is composed of grains and contains many voids.

The microwave surface resistance of a superconducting YBa2Cu3O7-δsingle crystal at 24 GHz was measured as a function of temperature and magnetic field. Below the superconducting transition temperature of 91 K, the microwave surface resistance rapidly decreased and was saturated below 75 K at zero magnetic field. Above 60 K, the microwave surface resistance increased linearly with the magnetic field. No hysteresis and no residual resistance were observed in the magnetic field cycling.

X-ray powder diffraction, thermal analysis and resistivity measurements have been carried out for the YBa2(Cu1-x , Co x )3O7-δ system with 0

Y-Ba-Cu-O superconducting tapes over 10 m long were prepared by an atmospheric plasma spraying method. The tapes were annealed at a maximum temperature of 900°C in an oxygen flow. The tapes consisted of a Y-Ba-Cu-O layer and a Ni alloy substrate. After annealing at 900°C, T c onset and T c offset of the tape were 94 K and 88 K, respectively. The critical current density at liquid nitrogen temperature was about 6 A/cm2 in the length range of 7.8 m. The superconductivity of the tapes was observed in the liquid nitrogen until it was bent to a curvature radius of 60 mm.

Heat treatment under high-pressure oxidizing atmosphere (oxygen partial pressure of 400 atm) is found to lower the T c of the superconductor YBa2Cu3O y . The powder X-ray diffraction pattern and the oxygen content measurement suggest that the excess oxygen occupies the oxygen defect site between the Ba-Ba layers.

Thick films composed of Y-Ba-Cu-O (e.g. 70 µm thick) were prepared on Ni alloy substrates at various temperatures by the atmospheric plasma powder spraying method. By increasing the substrate temperature during the spraying, the amount of unknown structure in the film sprayed was lowered and the structure of the film sprayed on 600°C substrate was tetragonal in phase. After the postannealing at 600°C, this film revealed superconducting temperatures for onset and zero resistance of 92 K and 86 K, respectively.