We measured I-V curves and noise characteristics of high-Tc YBa2Cu3Oy step-edge Josephson junctions and serial junction arrays under microwave irradiation. The junctions were fabricated on step-edge MgO(100) substrates with low step angles (∼30°). The junction array shows the resistively shunted junction (RSJ) behavior for at least 50 junctions and reveals a coherent phase locking under microwave irradiation. The variation of Ic was 16% for a 150-junctions array distributed along the step-edge line of 1.5 mm in width. The voltage noise, Sv, of the serial junction array scales as the number of junctions, N. The value of SIR, (SIR = |(δIc/Ic)∥(δR/R)|), for a single and 50-junctions obtained from the fluctuation measurement is consistent with the result derived from IcRn ∝ (Jc)q, with q = 0.5.
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