Abstract
YBa 2Cu 3O 7 direct coupled dc SQUID magnetometers based on the step-edge junctions on sapphire substrates have been fabricated. 15-nm-thick CeO 2 buffer layer and 120-nm-thick YBa 2Cu 3O 7 film were in situ deposited on the 35° steps formed on the sapphire substrates by Ar ion milling. Large I C R N product of 250 μV with junction resistance R N ∼ 5 ω and critical current I C ∼ 50 μA at 77 K could be obatined reproducibly with 5 μm microbridges. The SQUID magnetometers fabricated on the 1×1 cm 2 sapphire substrates based on the step-edge junctions exhibit a voltage modulation depth of 16μV and magnetic field noise of 170 fT/√Hz at 100 Hz for the 70 pH-SQUID.
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