Low surface resistance in YBa2Cu3Ox melt-processed thick films

Abstract

A LOWsurface resistance,R_s, is the key to successful development of radio-frequency and microwave applications of high-temperature superconductors. Here we report the Rs of YBa₂Cu₃O_x thick films on yttria-stabilized zirconia substrates at frequencies up to 50 GHz. Films processed below the peritectic temperature are fine grained, have R_s similar to bulk YBa₂Cu₃Or, generally have low critical current density (J_c) and exhibit little preferred orientation of crystallographic axes. Films processed above the peritectic temperature exhibit preferred orientation in large spherulitic grains, have higher J_c and far lower R_s. For these films the crossover frequency at which R_s equals that of copper is 50 GHz, a factor of two higher than the best bulk material or thick film yet reported and only a factor of ∼4 lower than high-quality thin films. At the frequencies used for mobile communications (900 MHz and 1.8 GHz), the superconductor losses would be two orders of magnitude lower than those of normal metals. The particular advantages of the thick-film route are the speed and low cost of the process, and the ability to apply the films on curved surfaces and on large areas, the largest so far being >200 cm².