High-Tc superconducting monolithic phaseshifter

A high temperature superconducting (HTS) X-band phase shifter using a distributed Josephson inductance (DJI) approach was designed and fabricated. Phase swings of over 60° were measured at 65 K and below, with measurable phase shifts at temperatures above 77 K. High quality HTS films and superconducting quantum interference devices (SQUIDs) were deposited by laser ablation. A total of 40 HTS step edge SQUIDs were successfully integrated into a monolithic HTS circuit to produce a phase shifter in a resonant configuration. The magnitude of the Josephson inductance is calculated and a lumped element model is compared to measurements     

High-Tc superconducting short dipole antenna

A recently discovered rare-earth copper-oxide material, which is superconducting above the temperature of liquid nitrogen, is used to fabricate a high-efficiency electrically short dipole antenna. Thus the necessity to cool a lead antenna structure to liquid helium temperatures is avoided. Results are presented which show the gain enhancement achieved using this new material when compared with a conventional copper structure at room temperature     

High-Tc superconductor waveguides: theory andapplications

The authors study the expected properties of future high-T_c superconductor waveguides. These devices offer the potential of 100 GHz of bandwidth for transmission over long distances with low attenuation, with the advantage over optical systems of wider dynamic range (providing a virtually unlimited number of taps). The authors study the theoretical performance of superconductor waveguides, including attenuation, carrier frequency and bandwidth, maximum transmitted power, and dispersion. The authors study the possible application of a single waveguide as the transmission medium for a 60-GHz (data rate) local area network     

High-Tc superconductivity seeks a digital home

Two obvious applications of high-T_c superconductors are discussed: the use of Josephson technology at 77 K and the use of high-T_c lines for interconnects. The difficulties that must be addressed for each of these is discussed, and the prospects for overcoming them are assessed. The need to achieve full compatibility with polymers is stressed     

High Tc superconducting active antenna withreflector

A high-T_c superconducting (SC) active antenna with a corner reflector is found to be useful for detecting electromagnetic waves (f=9.55 GHz). The SC active antenna is a new type of antenna which consists of material properties and antenna properties. The microwaves with fixed polarizations are radiated to the SC active antennas, and the detectivities and the directivities were confirmed experimentally. With the use of the corner reflector, the sensitivity and the directivity can be improved     

Microwave characteristics of high Tcsuperconducting coplanar waveguide resonator

A theoretical formulation has been developed to calculate the coupling coefficient, London penetration depth, and surface resistance of a coplanar waveguide resonator fabricated from films of superconducting YBCO material. Experimental data of the reflection coefficient as a function of temperature and frequency agree reasonably well with calculations. The formulation is of sufficient generality to be applicable to other guided structures     

Optical properties of high-Tc superconductors

The present status of optical spectroscopy of high-T_c superconductors is summarized. The optical properties of these materials resemble those of the more common transition metal oxides except for being highly anisotropic in the infrared (IR). This large IR anisotropy and a need to rely solely on reflectance techniques has hindered progress in obtaining accurate IR data and interpreting these data in terms of microscopic mechanisms. However, experimental consistency is now being approached with single-crystal samples, although interpretations of these data remain controversial and an unequivocal demonstration of a superconducting gap structure has not yet been achieved. The mid-IR exhibits an absorption band whose systematics are neither well established nor well understood. The situation in the visible-near-ultraviolet is better, partly because of greatly reduced optical anisotropy and the availability of alternative measurement techniques that are not strongly affected by the lower optical quality of sintered material. As polycrystalline, sintered samples can be prepared relatively easily over wide ranges of composition, doping, and chemical substitution, most work on studying the chemical systematics of these materials has been done in this spectral range and some of the structure that appears here has been positively identified     

Laser processing of high-Tc superconductingthin films

High-T_c superconducting thin films can be deposited and processed by pulsed and CW lasers, and a respectable materials technology for the Y-Ba-Cu-O superconductor is rapidly emerging. The pulsed laser deposition technique is simple because it produces films with compositions nearly identical to those of the target pellets. A larger variety of substrates can be used, compared to other deposition technologies, because of the relatively low temperature requirements. The laser deposition mechanism has been investigated. As-deposited superconducting films, epitaxial films with smooth surfaces, and multilayer structures with abrupt interfaces have been produced. The electrical transport properties can be changed locally using a focused argon-ion laser by modifying the oxygen stoichiometry. This laser writing can be erased by room-temperature exposure to an oxygen plasma. Other laser patterning methods such as material removal, melt-quench, and direct pattern transfer are being developed     

CMOS inter-chip interconnection circuit using high-Tc superconducting tunnel junctions and interconnections

The analysis of a possible low-voltage CMOS interconnection circuit utilizing high-T_c superconducting tunnel junctions (TJs) and interconnections for very-high-speed interchip communication at low temperatures (4-77 K) is presented. The circuit uses tunnel junctions as diodes to clip voltage swings between well-controlled levels defined by the energy gaps of the high-T _c materials. The circuit dissipates five to eight times less power than conventional designs, produces very small current transients, and has good immunity to noise from input voltage fluctuations, crosstalk, and simultaneous switching of drivers     

Design and performance of a high-Tcsuperconductor coplanar waveguide filter

The design of a coplanar waveguide low-pass filter made of YBa₂Cu₃O_7-δ (YBCO) on an LaAlO ₃ substrate is described. Measurements were incorporated into simple models for microwave CAD analysis to develop a final design. The patterned and packaged coplanar waveguide low-pass filter of YBCO, with dimensions suited for integrated circuits, exhibited measured insertion losses when cooled in liquid nitrogen superior to those of a similarly cooled thin-film copper filter throughout the 0 to 9.5 GHz passband. Coplanar waveguide models for use with thin-film normal metal (with thickness either greater or less than the skin depth) and YBCO are discussed and used to compare the losses of the measured YBCO and copper circuits     

Microstrip ring resonator technique for measuring microwaveattenuation in high-Tc superconducting thin films

Microwave attenuation of high-T_c superconducting (HTS) films sputtered on MgO and ZrO₂ were measured using a microstrip ring resonator circuit. The results of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O resonators were compared to those for gold-plated resonators of identical design. The losses of superconducting and gold-plated films were determined from unloaded Q-factor measurements. The attenuation of Y-Ba-Cu-O film on an MgO substrate is approximately 31% lower than that of gold films at 6.6 GHz and 33% lower at 19.2 GHz for temperatures below 50 K. The approach of using microstrips to characterize microwave losses shows the usefulness of HTS films in integrated circuit technology     

Quasi-optical millimeter-wave band-pass filters using high-Tc superconductors

Quasioptical millimeter-wave band-pass filters using YBa₂ Cu₃O₇ high-T_c superconducting films were fabricated on MgO and LaAlO₃ substrates. Transmitted power through the filter was investigated in the 75 GHz to 110 GHz frequency range at temperatures ranging from 15 to 300 K. At 15 K the measured center frequency and the bandwidth of the superconducting filter were 92 GHz and 0.85 GHz, respectively. Measurements of YBa₂Cu₃O₇ filters were compared with similar filters fabricated using gold. At 15 K and 92 GHz, an improvement of 75% in the quality factor of the superconducting filter was obtained compared with a similar gold filter     

Field theory investigation of high-Tcsuperconducting coplanar waveguide transmission lines andresonators

An investigation is conducted of a coplanar waveguide structure using a partial wave synthesis taking into account the complex conductivity of the high T_c superconductor material according to the two-fluid model and the London theory. Micrometer transmission line dimensions are considered in the frequency range up to 100 GHz. The results obtained for superconductors are also compared with the results obtained for superconductors with real conductivity and the same geometry. The behavior of measured and published coplanar waveguide half wavelength resonators made of high-T_c superconducting thin films is also examined     

Low-frequency magnetic shielding studies on high-Tc superconductor Y-Ba-Cu-O

Low frequency (10-Hz to 100-MHz) magnetic-shielding studies were performed on high-T_c superconductors Y-Ba-Cu-O to investigate the material's shielding behavior. The critical field H_c1 in the superconductor was observed to be ⩽17.8 G. The superconductor shielded down to the background noise level independent of the frequency when the applied field strength was⩽ H_c1. In the vortex state, just above H_c1, the superconductor-type transformer behaved nonlinearly. A semiempirical model for the skin depth was used to fit the nonlinear data. In the high applied field limit, this shielding data was shown to have a square-root frequency dependence similar to ordinary shielding materials. At lower fields above H_C1, data tended toward frequency independence. Noise-limited experimental low-frequency results indicated that the superconductor shielded at least as well as common state-of-the-art materials     

Testing of an inductive current-limiting device based on high-Tc superconductors

An inductive current-limiting device (CLD) based on transition of a superconductor to the normal state is investigated. The device has low impedance under normal conditions of the circuit to be protected, and a high impedance developed rapidly in a self-switching mode under fault conditions. A model of the device consisting of a copper coil and a high-temperature superconducting ring, coupled magnetically, was tested. It is shown that the transition of the ring to the normal state and its return to the superconducting state take place in a relatively smooth manner, and do not lead to overvoltages across circuit elements. On the other hand, the rate of impedance rise is sufficient to limit both the steady-state and transient components of fault current. The influence of thermal processes in the ring on transient responses in the circuit with the CLD is discussed. Some considerations for a full a size design are also presented     

Generalized spectral-domain analysis for multilayered complex mediaand high-Tc superconductor applications

An efficient algorithm for rigorously deriving the spectral-domain impedance dyadic Green's function for MMICs on general complex anisotropic or bi-anisotropic substrates is developed. Its main advantage is that it provides closed-form expressions for transverse propagation constants and related immittances in the spectral domain and, therefore, allows the following parameters to be taken into account: dielectric and magnetic losses of anisotropic or bi-anisotropic media without restrictions to the magnitude of tensor elements, alternative directions for magnetic bias, and the finite metallization thickness of conventional conductors and/or superconductors including their losses. Microstrip and coplanar waveguide structures in open, shielded, and conductor-backed technology can be treated. The theory is verified by comparison with previously published data, and its flexibility is demonstrated for both superconductor and conventional conductor (M)MIC structures     

High Tc wire design and power losses on cyclingSMES devices

The present state of the art in high T_c superconductors is projected to the kilometer-long wires needed for a superconducting magnetic energy storage (SMES) device. It is concluded that silver-clad-bismuth-based superconductor is the only form which is likely to be available in the near future. This wire should have a cross-section of approximately 1 cm² and carry 10 kA in fields up to 10 T. For satisfactory performance it must be made in the form of twisted multifilaments rather than the flat tape form which is presently receiving the most attention. In addition, detailed measurements of J_c as a function of field and temperature of the wire form as well as thermal conductivity and heat capacity are required in order to properly calculate the stability limits of the wire     

Full-wave characterization of high-Tcsuperconducting transmission lines

A full-wave numerical analysis is applied to accurately characterize superconducting transmission lines embedded in a layered dielectric medium. A volume integral equation formulation is developed by using a spectral domain dyadic Green's function for stratified media. Galerkin's method with rooftop basis functions for the electric field distribution inside the superconductor is then employed to solve the complex propagation constant. The thickness of the superconducting film is arbitrary in this analysis, and the formulation rigorously accounts for the anisotropy of the superconducting film. The propagation characteristics of a superconducting microstrip transmission line with a thin dielectric buffer layer are investigated. A superconducting stripline configuration with an air gap is also studied     

Potential methods for the fabrication ofhigh-Tc superconductors for wires and cables

Studies of practical properties, such as upper critical field (H_C2) and critical-current density, of high-T _c oxide superconductors of Y-Ba-Cu-O Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O systems are reviewed. The H_c2 of these materials is much higher than that of conventional metallic superconductors, indicating a high potential for practical applications, even when they are used in liquid nitrogen. However, the H_C2 of these materials is also highly anisotropic, as can be expected from an examination of their crystal structure. In addition to this anisotropy, the presence of weak links and a weak pinning force in this material limit the transport current density J₃ to much lower levels than that required for practical applications. Recent fabrication processes that have good potential for producing wire or tape conductors or high-T_c oxide are reviewed. Some details are presented of the powder method and other fabrication processes using diffusion, solidification, and deposition techniques. For the Ag-sheathed oxide tapes, J_c values exceeding 10000 A/cm² at 77 K and 0 T have been reported for both Bi and Tl oxide materials