Reproducible step-edge junction SQUIDs

High-T/sub c/ superconducting YBCO SQUIDs have been developed based on step-edge junctions. The step-edges were fabricated by using electron-beam lithography and Ar-ion milling on SrTiO/sub 3/ substrates. The V(/spl Phi/) peak-to-peak voltage is around 10 /spl mu/V, and the I/sub c/R/sub n/ product is 150 /spl mu/V at 77 K. The SQUIDs prepared on the same substrate show reproducible parameters within 30%. At 77 K the noise properties of the SQUIDs have been studied. At lower frequencies (1 Hz-100 Hz), we observe a flat noise level just below 10/sup -4//spl Phi//sub 0//Hz/sup 1/2/ probably limited by switching effects. Above 100 Hz the noise is gradually reduced to 10/sup -5//spl Phi//sub 0//Hz/sup 1/2/ at 1 kHz. The geometry of the step-edges has also been investigated by scanning electron microscopy, and the relation between the properties of the SQUID and the step height is reported.<
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