The in-situ growth of the superconducting Ba1-x K x BiO3 (BKBO) films as a function of oxygen partial pressure and substrate temperature by laser ablation has been studied. The superconducting BKBO films can be grown at a temperature of 410-500°C within two pressure ranges of 15-60 mTorr and 200-400 mTorr, respectively. Oxygen partial pressure was found to be important to control the growth of the superconducting BKBO films. The optimum pressure for growing the superconducting BKBO films is 40 mTorr, under which potassium is readily doped into the BKBO phase by oxygen. In the present study the best film with T c(onset) of 28 K and T c(zero) of 25 K is grown at 450°C in 40 mTorr of O2.

An adjustable multilayer high-temperature superconductor (HTS) bandpass filter has been fabricated. Taped comb-line filters with multilayer structures were designed. YBa 2 Cu 3 O 7 (YBCO) thin films deposited on LaAlO 3 were used to construct the packaged multilayer HTS filter. The electrical length of the resonators in the filter was smaller than a quarter-wave length. The frequency responses of the filter were measured at liquid nitrogen temperature 77 K. The insertion loss of the packaged filter was determined to be less than 0.5 dB. By mechanically adjusting the multilayer structure, the center frequencies of the filter changed from 1.78 to 1.92 GHz, and the variations of the bandwidth from 60 to 150 MHz were also obtained.

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