Progress, properties and prospects of passive high-temperature superconductive microwave devices in Europe

Abstract

The technology of high-temperature superconductors has become mature. Various methods to analyse and optimize the temperature and microwave field dependent surface impedance have been developed. Promising applications of passive microwave devices have been identified between 0.01 and 10 GHz. This progress profits from improved design and simulation tools, aimed at miniaturizing the circuits at optimum performance and integrating them into realistic systems. Important facets of these developments are sketched in terms of their physical basis and illustrated with selected examples of filters, stable oscillators and MRI antennas.

Nonlinear microwave properties of HTS thin film coplanar devices

“…4(b)) of as a function of effective magnetic field for a typical set of zfc and fcs experiments demonstrates the excellent agreement of the data with the prediction in (5).…”

“…However, in contrast to their normal-conducting competitors, the power handling capability of superconducting microwave devices is limited by the onset of nonlinear effects in form of a strong increase of the dissipation or intermodulation products at large rf power. Although various physical origins are discussed (e.g., weak links in granular superconductors [2], pair breaking [3], thermal effects [4], magnetic effects [5]), the physical mechanism, that is responsible for the nonlinear surface resistance and that represents a serious restriction for a number of rf applications, is not fully understood. In this paper, we demonstrate that the combination of vortex matter and microwave properties leads to new insight into the nature of the nonlinear microwave properties of superconducting material.…”

Fundamental microwave-power-limiting mechanism of epitaxial high-temperature superconducting thin-film devices

“…Field-driven mechanisms are usually explained by a deterioration of the microwave properties due to the penetration of vortices if the surface magnetic rf field exceeds a certain limiting value of the order or based on B c1 . 6,7 However, by comparing measurements on devices with different-magnetic field configurations, it is argued that a field-driven mechanism cannot consistently describe the onset of nonlinear effects for all field configurations. 8 Current-driven mechanisms are usually based on the onset of nonlinear effects if the rf transport current density exceeds a certain limiting value which is characteristic of the nonlinear mechanism.…”

Fabrication, Structure and Properties of Tl-Based HTS Thin Films

“…The TI-2212, Tl-2223 and TI-1223 phases have critical temperatures in the range 100-120K; thus at the proposed operating temperatures of -80K, readily achievable with single-stage cryocoolers, their superconducting properties exhibit a slow variation with temperature, thus obviating the need for precise temperature control in maintaining device performance [1]. Device quality films of the above phases have been deposited on a variety of substrates, with and without buffer layers, by a number of groups and a range of practical microwave components have been successfully demonstrated [2]. Critical current densities at 77K and in zero field in excess ofGAni 2 , and surface resistance values, normalised to 80K and 10GHz, <0.…”