We have successfully fabricated YBCO Josephson junctions and SQUIDs with variable thickness bridges. The variable-thickness bridges of YBCO thin film were fabricated by photolithography and Focused ion beam mill. The Josephson effects of variable thickness bridges were obtained in a 80 nm-thick-film of high-c YBa 2 Cu 3 O y . The Shapiro steps were observed in single junction in the gigahertz range from 3.02 to 14.64 GHz. The voltage-current and voltage-field characteristics were measured in SQUID magnetometer. The SQUID shows a peak-to-peak voltage swing of 1.5 V at 70 K. The properties of one junction and SQUID magnetometer have been investigated. Index Terms-Focused ion beam, Josephson junction, variable thickness bridges.
High-T c Josephson junctions were successfully fabricated by focused ion beam (FIB) direct milling. The characteristics of the junction barrier were carefully controlled by tuning the thickness of the link region. The optimal remaining thickness for the YBCO is about 70-80 nm even though the YBCO thicknesses are different. The temperature-dependence of the critical current provides good evidence of the superconductor-normal-superconductor weak link of the junctions. Although the flux-flow behavior increasingly dominates at lower temperatures, the voltage-current shows resistively shunted junction-like characteristics at temperatures close to T c . The Shapiro steps of a single junction irradiated with microwaves were measured, revealing strong Josephson effects in ion-damaged junctions. This method will be of great benefit to nanoSQUIDs for the detection of spin systems.
The effect on effective area and voltage modulation depth of a serial superconducting quantum interference device (SQUID) magnetometer was simulated and observed. The variation in the effective area with the number N of serial SQUIDs was simulated. To reduce the beat phenomenon and optimize the serial SQUID magnetometer, the distance x between two adjacent SQUIDs should exceed 40 mu m or even 65 mu m, or dummy SQUIDs should be added at the edge of the serial SQUIDs. The optimal layout of a high-T(c) serial SQUID array is discussed. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2990069
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