High frequency properties of YBCO bridges fabricated by MOCVD

The high-frequency properties of YBCO (YBa₂Cu₃ O_7-δ) bridges at 4.2 K and 77 K are discussed. The YBCO films were prepared by MOCVD. For small bridges with a width ( w) of about 1 μm and thickness (t) of less than 0.5 μm, the constant voltage steps at integral multiples of Φ₀ fr-20 μV were observed up to 1 mV, which is much higher than the I_cR_N (<0.13 mV) product of these bridges at 77 K. The magnitudes of the current steps as functions of the RF current at 4.2 K and 77 K were in quantitative agreement with the theoretical results based on the RSJ (resistively shunted junction) 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 μm and t=1 μm, 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