High Temperature Superconducting Microwave Devices Research Articles

Microstructure study of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-<i>δ</i></sub> thin film with synchrotron-based three-dimensional reciprocal space mapping

High-temperature superconducting films can be used for fabricating the cutting-edge high-temperature superconducting microwave devices because of their low microwave surface resistances. However, the microwave surface resistances of high-temperature superconducting materials are particularly sensitive to microstructure due to their special two-dimensional superconducting mechanisms and extremely short superconducting coherence lengths. To investigate the correlations between microstructure and microwave surface resistance of high-temperature superconducting materials, YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-<i>δ</i></sub> (YBCO) films with different thickness are grown on (00l)-oriented MgO single-crystal substrates by using the pulsed laser deposition (PLD) technique. Electrical measurements reveal that their superconducting transition temperatures and room temperature resistances do not show significant difference. However, their microwave surface resistances in superconducting state display a significant difference. The characterizations of the microstructures of YBCO films by synchrotron radiation three-dimensional reciprocal space mapping(3D-RSM) technique show that the number of the grains with CuO<sub>2</sub> face parallel to the surface (c crystals), and the consistency of grain orientation are the main causes for the difference in microwave surface resistance.

Closed Form Formulas for Distributed Circuit Model of Discontinuities in HTS Microstrip Transmission Lines

A distributed circuit model for different kinds of discontinuities in high temperature superconducting (HTS) microstrip transmission lines (TLs), is proposed. In each case, closed form formula for lumped element model is presented based on the configuration of the discontinuity and the characterizations of HTS microstrip TLs. These discontinuities consist of steps in width, open ends, gaps and 90-degree bends. In the case of normal conductor microstrip TLs there are a lot of numerical and analytical equations that can accurately model them, however those formulas are not efficient for HTS TLs. Thus modified relations are extracted utilizing the superconducting characterizations to obtain much more accurate formulas. Additionally temperature dependence of HTS TLs is considered in the relations. Moreover regarding the kinetic inductance in HTS TLs a closed form formula is proposed for characteristic impedance of HTS TLs. Furthermore correction factors based on fringe fields is used to optimize all formulas. Using these formulations can lead to modeling and analysis of some superconducting microwave devices such as resonators, microwave filters, couplers, etc. In contrast to EM analysis, using the distributed circuit model is much easier for analysis of HTS microwave devices. The accuracy of the proposed model is confirmed in comparison with some electromagnetic full-wave simulations. This full analytical approach shows great accuracy in this test case as well.

Efficient characterization of EMC shielding in anisotropic high-Tc superconducting devices for industrial applications

In this article, an efficient full-wave-mode algorithm has been developed to efficiently address industrial needs for rigorous characterization of electromagnetic compatibility shielding effects in anisotropic high-temperature superconducting microwave devices on lossy anisotropic dielectric substrates in multilayer configuration. Finite thickness and conductivity as well as anisotropy of the superconducting films have been investigated. The proposed formulation uses the spectral domain dyadic Green's functions for stratified media. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Investigation of HTSC digital trunking communication receiver subsystem

The application of HTSC (high temperature superconductor) microwave devices in a UHF digital trunking communication system is introduced. The replacement between the HTSC microwave devices and the normal microwave devices is conducted. The digital sensitivity of the base station in complex electromagnetic environment has been increased to 6 dB, as the results of the experiment indicated, and this means that the coverage radius of the base station has been improved about twice, that is to say, the coverage area can be extended to four times as large as that of the current method.

Nonlinear buffer layers relevant for reduced nonlinear effects in HTS microwave devices

Microwave devices made of a High-Temperature Superconductor (HTS) exhibit a nonlinear response as the microwave power increases. The HTS nonlinearities generate a nonlinear inductance Ld(irf) and a nonlinear resistance Rd(irf) in a device. Ld(irf) and Rd(irf) are responsible for an increase of the device loss, a small frequency dispersion as well as the generation of spurious signals like Intermodulation Distortion (IMD). Nevertheless, the HTS nonlinearities in a microwave device can be reduced using a nonlinear dielectric like a ParaElectric Material (PEM). This assumption has recently been demonstrated theoretically. In a microwave device made of a HTS and a PEM, the nonlinear contribution to the capacitance Cd(vrf) from the PEM acts oppositely to the nonlinear contribution to Ld(irf). This may cancel the effect of the HTS inductive nonlinearities. The PEM also produces a nonlinear conductance Gd(vrf) in a device. All these nonlinear terms contribute to the IMD output power and the nonlinear quality factor (Q0) of a resonant passive microwave device. In this paper, the dependence of the different nonlinear contributions on frequency and applied dc bias voltage (Vdc) is investigated. The relevance to employ PEM in order to reduce the nonlinearities in HTS microwave devices is discussed.

Unified Description of Nonlinear Effects in High Temperature Superconductor Microwave Devices

We experimentally demonstrate the equivalence of different manifestations of nonlinear response in high temperature superconductor (HTS) microwave devices. Using a combination of analytical and numerical analysis, we show that the results of intermodulation distortion measurements, harmonic generation measurements, and power-dependent resonator measurements of different coplanar waveguide structures patterned onto the same HTS thin-film sample all yield approximately the same values for the nonlinear penetration depth. The extraction of an underlying nonlinear material parameter that is independent of the specific device geometry and experimental configuration will allow our results to be quantitatively compared with other nonlinear measurements, and will therefore help in determining the dominant source(s) of nonlinear response in HTS microwave devices.

Analysis of a flip-chip bonded tunable high-temperature superconducting coplanar waveguide resonator using the conformal mapping technique

We have studied the tuning properties of a high-temperature superconducting (HTS) half-wavelength coplanar waveguide (CPW) resonator operating at 5 GHz. The tuning schemes are based on flip-chip bonding of an electrically tunable ferroelectric (FE) thin film and a mechanically movable low-loss single crystal on top of the resonator. Using the conformal mapping method, closed-form analytical expressions have been derived for a flip-chip bonded conductor-backed and top-shielded CPW transmission line. The obtained expressions are used to analyse the volume effect of the FE thin film and the gap between the flip-chip and the CPW resonator on the tuning properties of the device. It has been found that large frequency modulation of the resonator produces impedance mismatch, which can considerably enhance the insertion loss of high-performance HTS microwave devices. Analysis also suggests that, for electrically tunable devices, flip-chip bonded FE thin films on HTS CPW devices provide a relatively higher performance compared to bilayer HTS/FE tunable devices.

Microwave superconductivity

This paper provides an overview of the microwave applications of high-temperature superconductor (HTS) technology. The main characteristics of HTS materials are outlined, highlighting the differences between superconductors and normal conductors. This paper presents recent progress in the development of HTS filters, multiplexers, cryogenic receivers, delay lines, and antennas. A brief summary of cryocooler technology and cryopackaging requirements is presented. The benefits of using HTS technology in wireless and satellite systems are also discussed. The intent of this paper is to provide perspective to newcomers in the field and to empower the potential end-users with current status and performance capabilities of HTS microwave devices.

Optical-microwave interaction modeling in high-temperature superconducting films

Optical-microwave interaction in high-T/sub c/ superconductors is investigated for performing basic optoelectronic functions in cryogenic environment. A fast bolometric photoresponse in conjunction with the unique electrical properties of high-temperature superconductor (HTS) materials allows us to explore a series of novel optoelectronic devices with low-noise/low-power and high-speed/high-frequency characteristics. After reviewing the HTS photoresponse categories, we describe the fast bolometric photoresponse and its condition with heat transfer analysis. The analytical solution of heat diffusion equation for an HTS strip mounted on a substrate will be presented for three different type of optical sources. Then the effect of optical irradiation will be incorporated in the two-fluid model by thermomodulation concept in order to model the interaction of optical radiation with electrical signal. The current-field relationship and the supercurrent response time are evaluated in the presence of both optical and electrical signals. Our numerical simulations for YBaCuO film demonstrate the possibility of RF harmonic generation when the laser beam is modulated by the RF signal in the presence of dc bias current and RF signal mixing when the HTS film is fed by a time-harmonic microwave source. The developed model can also be used to study optical control and tunability techniques for HTS microwave devices for analog signal processing.

Geometry dependence of nonlinear effects in high temperature superconducting transmission lines at microwave frequencies

We investigate the nature of low-power nonlinear effects in high-temperature superconducting microwave devices by measuring third harmonic generation at 76 K in coplanar waveguide transmission lines of different geometries fabricated from YBa2Cu3O7−δ thin films. The measured power in the third-harmonic signal changes systematically with film thickness, center conductor linewidth, and line length. We analyze these results using a simple model for a transmission line with a nonlinear inductance arising from a current-dependent superconducting penetration depth. This analysis describes quantitatively the observed differences in harmonic generation for transmission lines of different dimensions, and yields a single geometry-independent parameter (the nonlinear scaling current density J0) to quantify the observed nonlinear behavior. For the thin film samples studied here J0=3.0×107 A/cm2 at 76 K for all geometries investigated. These results provide the means to establish a lower limit for the expected nonlinear response of superconducting components of arbitrary geometry at microwave frequencies.

Electrical tuning of passive HTS microwave devices using single crystal strontium titanate

Over the last few years several groups have fabricated High Temperature Superconducting (HTS) thin film microwave devices which have included a ferroelectric thin film layer in their design. The electric field dependence of the ferroelectric promises desirable in-situ tuning of the frequency response. Here we present the results of our experiments on the tuning of a coplanar HTS resonator using single crystal strontium titanate (STO). We have patterned a simple coplanar resonator device onto Y-Ba-Cu-O thin films deposited on [100] magnesium oxide substrates. Careful consideration of the size, position and biasing of these high permittivity STO crystals with respect to the planar device allows us to minimise the perturbance to the plain resonators response whilst at the same time maximising the degree to which we are able to tune the device. We have also performed a series of capacitance measurements on our STO crystals to obtain reliable data for the dependence of the permittivity on temperature, applied bias and crystallographic orientation.

Microwave applications of high-temperature superconductors

The major advance in the area of high temperature superconducting microwave devices has been in the incorporation of high performance devices (based on planar transmission line structures or shielded dielectric resonators) into microwave receiver systems with performances equivalent or better than those of conventional systems. These systems include reliable closed-cycle coolers that can allow access to the low temperatures required for efficient operation (<80K). Nonlinear effects at high powers have previously presented a drawback for these novel devices, but superconducting thin film disc resonators, operating in modes with radial current flow (in addition to compact, shielded dielectric resonators), do not suffer from the very high microwave edge current densities present in planar structures, and have demonstrated very encouraging microwave power handling capabilities.

Large area double-sided YBa2Cu3O7−δ films grown by single-source metal-organic chemical vapor deposition

Thin films of YBa2Cu3O7−δ were sequentially grown on both sides of 3 in. diameter LaAlO3 substrates by a single-source MOCVD technique to facilitate the fabrication of double-sided high temperature superconductor microwave devices. YBCO films on both sides of the LaAlO3 substrates had thicknesses greater than 4000 Å, Tc’s of 87–88.5 K, and microwave surface resistances as low as 23 mΩ at 94 GHz and 77 K (scaling to 260 μΩ at 10 GHz). It was found that the substrate temperature, brought to the desired value by radiant heating, played a critical role in the deposition of very low surface resistance YBCO films. Microwave bandpass filters with a 19-pole forward coupled configuration were fabricated from these films. The filters showed excellent performance with dissipation losses as low as 0.5 dB.

High-temperature superconducting microwave devices: Fundamental issues in materials, physics, and engineering

High-T c superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T c superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T c superconducting films are discussed, with a focus on thin films of the HTS material YBa2Cu3O7−δ. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.

The Materials, Physics and Engineering of High Temperature Superconductor Microwave Devices

The Materials, Physics and Engineering of High Temperature Superconductor Microwave Devices