HIGH-FREQUENCY PROPERTIES OF YBCO BRIDGES FABRICATED BY MOCVD

We report on the high frequency properties of YBCO bridges at 4.2K and 77K. The YBCO films were prepared by MOCVD. For small bridges with the width(w) of about 1-mu-m and thickness(t) of less than 0.5-mu-m, the constant voltage steps at integral multiples of PHI-(o)fr = 20-mu-V were observed up to 1mV, which is much higher than the IcR(N)(< 0.13mV) product of these bridges at 77K. The magnitudes of the current steps as functions of the rf current at 4. 2K and 77K were in quantitative agreement with the theoretical results based on the RSJ model. The dc SQUIDs with these small bridges had a good response to external magnetic flux, resulting in a sinusoidal current-phase relation. On the other hand, for large bridges of w > 5-mu-m and t = 1-mu-m, the chaotic I-V characteristic was observed, and the shape of chaotic I-V curve was in qualitative agreement with the simulating results based on an RSCJ model.