SNS Josephson Junctions and DC SQUIDs
The properties of YBaCuO/Ag/YBACuO Josephson junctions and SQUIDs are presented. The junctions were prepared in situ across a step edge on MgO substrates. The influence of the silver deposition temperature on the electrical properties of the junctions has been investigated. Higher deposition temperatures reduce the contact resistance perpendicular to the c-axis of YBaCuO. This results in a low resistive shunt of the SNS contact, which decreases the I c R N product. Junctions were fabricated with different preparation parameters. The properties of the SQUIDs can be adjusted [R N from 5 mΩ to 1 Ω, I c from 0.2 mA to 3 mA (at 10 K)]. The low-resistance junction offers good reproducibility. The voltage modulations of the SQUIDs, which are not yet optimized, are of the order 3.5 μV at 50 K and 0.2 μV at 77 K. An upper limit of the flux noise, ø n , of < 80 μø 0/Hz1/2 and of the energy sensitivity, є n , of <6.8.10−28 J/Hz measured in the direct mode was determined for f >1 kHz.
KeywordsContact Resistance Josephson Junction Normal Metal Photoresist Mask Energy Sensitivity
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