Surface resistances of 5-cm-diameter YBCO films prepared by MOD for microwave applications

Abstract

Large-area high-Tc superconducting films with low surface resistances Rs are required for use in microwave applications such as band pass filters. In this paper, preparation of 5-cm-diameter YBCO films on LaAlO3 (LAO) and CeO2-buffered sapphire (CbS) substrates by metalorganic deposition (MOD) using a fluorine-free coating solution and their superconducting properties are described. The optimum firing conditions for YBCO films greatly depend on the substrate materials; a heating rate at ramp as high as 200°C/min is necessary for films on LAO whereas a lower heating rate, e.g., 20°C/min, is required for films on CbS. Accordingly, the suitable furnace systems for these substrates have been varied. As a result, a YBCO film with high Jc (77K) of 2.7MA/cm2 and a low Rs (12GHz, 77K) of 0.54mΩ was prepared on LAO by using an infrared image furnace. On the other hand, a YBCO film with a higher Jc (77K) of 4.0MA/cm2 and the same Rs (12GHz, 77K) of 0.54mΩ was prepared on CbS by using a tube furnace.