Measurements and modeling of HTS shielded dielectric resonators

Abstract

We have performed accurate, reproducible and nondestructive measurements of the surface resistance of high quality YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films in the temperature range 12 K to T/sub c/ using a compact rutile dielectric resonator method at 9.6 GHz. The absolute values of the HTS surface resistance have been measured to systematic errors of less than 10 /spl mu//spl Omega/ at this frequency using this technique, which employs two resonator configurations with carefully chosen geometries. The resonators have unloaded Q factors of around 10/sup 5/ at 77 K, increasing to above 5.10/sup 5/ below 15 K. We have used three dimensional electromagnetic software ("Superfish") to study the effects of the copper shield on these rutile (TiO/sub 2/) measurements, and others using lanthanum aluminate (LaAlO/sub 3/) as the dielectric material. In the latter case, there are significant uncertainties (as large as 100%) in the measurements of the surface resistance of the YBCO films owing to the smaller field energy filling factor for LaAlO/sub 3/ since it has a lower relative permittivity than rutile.