Fabrication and characterization of high-T/sub c/ superconducting X-band resonators and bandpass filters

摘要

Microstrip passband filters with 3, 6, and 11 poles, as well as microstrip resonators, have been fabricated using postannealed Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ (YBCO) films deposited on LaAlO/sub 3/ substrates using three-target simultaneous co-sputtering. The insertion loss in the passband for the filters with center frequencies between 9.5 and 13.4 GHz was >or=0.3 dB at 50 K and >or=0.6 dB at 77 K for the three- and six-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 postannealed 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 Q values 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 Q values and resonant frequencies of the resonators.