FABRICATION AND CHARACTERIZATION OF HIGH-TC SUPERCONDUCTING X-BAND RESONATORS AND BANDPASS-FILTERS

Microstrip passband filters with 3, 6, and 11 poles, as well as microstrip resonators, have been fabricated using post-annealed Y1Ba2Cu3Ox (YBCO) films deposited on LaAlO3 substrates using 3-target simultaneous co-sputtering. The insertion loss in the passband for the filters with center frequencies between 9.5 and 13.4 GHz was less-than-or-equal-to 0.3 dB at 50K and less-than-or-equal-to 0.6 dB at 77K for the 3 and 6 pole filters, respectively. The out of band rejection was greater than 50 dB. The excellent filter performance was attributed to the use of highly c-axis oriented post-annealed YBCO films. The quality of these films depended strongly on substrate preparation, film thickness, density of YBCO grain boundaries, and crystallographic orientation of the grains. Microstrip ring resonators fabricated with optimized YBCO films had Qs as large as 3800 at 9.5 GHz. The surface resistance and penetration depth for the YBCO films were determined from the temperature dependence of the measured Qs and resonant frequencies of the resonators.