I-V, V-@ characteristics and atomic force images of grain boundary Josephson junctions fabricated on SrTiO, bicrystal substrates were investigated. The half integer Shapiro steps and I, versus B curves show evidence of the inhomogeneous current distribution along the grain boundary junction. The dc SQUID formed on the grain boundary shows the expected V-CD curve. The AFM images, R-T curves and I,R, product reveal sequential destructive deterioration of the junction originating from the underlying grooved substrate. The results are discussed.
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.
We have designed and fabricated the directly coupled YBa2Cu3O7.s dc SQUID magnetometers with two different modulation schemes to study the crosstalk effect in the on-chip multi-channel magnetometers. In one of the modulation schemes, the modulation current was directly injected into the SQUID body and the pick-up coil. The modulation efficiency was changed by the ratio of the modulation current flowing through the SQUID to the pick-up coil. In the other schemes, the modulation flux is mutually coupled through an external coil, and the modulation efficiency was changed by the mutual inductance of the external coil and the magnetometer. The results show that the modulation efficiency was varied when the value of self-inductance or the mutual inductance of SQUIDs change. Usually, lower modulation efficiency results in a higher crosstalk. The performance of magnetometers was also influenced by different modulation schemes. Their noise spectrum was compared as evidence.
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