| In order to fabricate step edges on the substrates of MgO(100) and SrTiO₃ into preferable forms, ion beam milling processes with various parameter sets were investigated. The beam energy and the incident beam angle being varied, the step angles >50 degrees for MgO and >65 degrees for STO were possible to obtain by adjusting the beam angles to be 10 and 15 degrees, respectively. The step edges possessing steep angles and clear-cut aspects were confirmed through examinations under an SEM and an AFM. Thin films of YBa₂Cu₃O_(7-d)(YBCO) deposited on the stepped substrates by using off-axis magnetron sputtering methods yielded reasonably high quality specimens with their critical temperatures T_c>90 K and critical current density J_c> 3×10^5 A/㎠ as measured at the boiling temperature of nitrogen 77 K. Being patterned and dry etched for SQUIDs (superconducting quantum interference devices) to possess the line width as small as 2 microns by utilizing ion beam technology, these films showed no degradation in terms of T^c and J^c. The I-V (current-voltage) characteristics of these SEJ-SQUIDS revealed Josephson AC and DC effects. Based on the data obtained for the critical current of SQUID Ic.SQ measured at various temperatures, the value of I^(C,SQ) for the case of 77 K was predicted as 4.0 microA. Further, microwaves applied to these prototype devices rendered Shapiro steps in the I-V curves. It was. therefore, concluded that these Josephson devices evidenced a strong feasibility in use at the liquid nitrogen temperature 77 K. |
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