Temperature depeddence of the microwave surface resistance of YBCO thin films from microstrip resonator measurements

• Published in: Physica. C, Superconductivity Superconductivity, 1991-05, Vol.175 (5), p.603-606
• Main Authors: Gergis, I.S., Kobrin, P.H., Cheung, J.T., Sovero, E.A., Lastufka, C.L., Deakin, D.S., Lopez, J.
• Format: Article
• Language: English
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/0921-4534(91)90272-Z

The surface resistance of YBa 2Cu 3O 7− x (YBCO thin films were obtined from measuring the Q-factor of inverted microstrip resonators at 6–7 GHz over the temperature range of 16–80 K. The inverted microstrip which included a sapphire spacer between the YBCO line and a YBCO ground plane has lower dielectric loss than of regular microstrips since sapphire has a much lower tangent than that of the film substrate. This enables the determination of R s to a much higher sensitivity. We have examined good quality epitaxial YBCO films fabricated by several techniques; ion beam sputtering, pulsed-laser deposition, and off-axis magneton sputtering. Most films have T c's of 85–90 K and J c of 0.5−2×10 6 A/cm 2 at 77 K. The loaded Q-factors were 2500–4800 at 77K increasing up to 77 000 at 16 K, which, to our knowledge, is the highest Q measured for a high- T c microwave planar resonator. We have found that the surface resistances of the YBCO films of comparable T c and J c have similar values at relatively high temperatures ( T>70 K) even though these films were grown by different techniques. The surfaces resistance, scaled to 10 GHz was in the range 0.44−0.7 Ωm at 77 K and as low as 37 μΩ at 16 K.