Quality factor and surface resistance of high-Tc superconductor thick film microstrip resonators

Quality factor and surface resistance of high-Tc superconductor thick film microstrip resonators have been studied at various cryogenic temperatures. Superconducting microstrip line resonators made of YBa2Cu3O7-d (YBCO) material were prepared by screen printing on polycrystalline yttrium stabilized zirconium oxide substrates. Equivalent resonators mae of thick film gold material (ESL 8880-H) were prepared on the same substrate material to determine the resonator geometry factor (G) and by means of it the surface resistance (RS) of the superconducting resonators. Both conductor patterns and ground planes of the superconducting resonators were made of YBCO material. The resonators were measured in the frequency range 2 GHz - 7 GHz and the temperature range 30 K - 90 K (the gold resonators were measured up to 300 K). At their best, the superconducting resonators showed significant improvement in unloaded quality factor Q0 (over three times higher) and over 6 dB lower insertion loss values compared to identical thick film gold resonators at 40 K - 50 K temperatures. The crossover temperature was frequency dependent: for example, temperatures of 62 K at 2.3 GHz, 71 K at 4.6 GHz and 55 K at 6.8 GHz frequencies were observed. The surface resistance of the YBCO resonators was calculated at the fundamental, the second and the third harmonic resonant frequencies at 40 K and 77 K. To achieve significant improvement in loss characteristics over thick film gold resonators at these frequencies, operation near 40 K temperatures is required.