Microwave Properties of Bi2223 Thick Films on Ba(Sn, Mg, Ta)O₃ Dielectric Disk

Abstract

We fabricated 2.1GHz TM₀₁₀-mode microwave resonators with (Bi, Pb)₂Sr₂Ca₂Cu₃O_x (Bi2223) superconducting thick films on a Ba(Sn, Mg, Ta)O₃ dielectric disk with a relative dielectric constant of ε_r=24. The Bi2223 thick films were screen-printed on both sides of the dielectric disk and subjected to a double repetition of cold isostatic pressing at 0.4GPa and sintering at various temperatures ranging from 820 to 840°C. An increase of the sintering temperature raises the Bi2223 phase purity up to 98% on the surfaces of the thick films, but high-temperature sintering above 830°C causes a chemical reaction at the interface between the Bi2223 thick film and the dielectric disk. An optimization of the sintering temperature to 830°C gives the unloaded quality factors Q_u as much as 74, 000 at 70K and 158, 000 at 25K, which correspond to surface resistances R_s of 0.34 and 0.15mΩ for Bi2223 thick films, respectively. These values are approximately 20 times higher than those for the resonator using Ag electrodes with the same structure.