New techniques for fabricating step-edge junctions for high-T/sub c/ SQUIDs on MgO substrates

Abstract

Absiract-High quality reproducible junctions are mandatory in the construction of high-?', RF and DC SQUIDs using YBazCu307-, thin films. In this paper, we describe two methods used to produce step-edge junctions on MgO substrates suitable for SQUID devices. In both processes a titanium mask has been used to produce a straight, well defined step which assists, in minimizing the occurrence of multiple junctions. We describe two ionmilling processes which produce differently connected stepedge junctions as indicated by SEM micrographs, I-V and I,-B characteristics. Predictable relationships between the ratio of the film thickness t o step height and the junction critical-current density are demonstrated; these enable the creation of step-edge junctions with appropriate values of I, for particular SQUID designs.

Optimization and passivation of HTS step-edge Josephson junction rf SQUIDs

“…The optimum ratio is lower than most reported values in the range of 0.5-1.0 [1]- [3], [5], [7], [8]. It is also significantly different from our rf SQUIDs of the same structure but fabricated using sputtered films for which is often 0.7.…”

“…Rf SQUID magnetometers were fabricated from YBCO thin films using our step-edge technology described in [3], [4]. The step structures were prepared on 10 mm 10 mm MgO (100) substrates with step angles in the range of 35 -40 and heights in the range of 370-470 nm.…”

“…The suitable ratio, however, depends on the microstructure of the step and the characteristics of the YBCO film which varies for different step angles and film growth techniques. Initially, we fabricated a large number of rf SQUIDs by using an in-house DC magnetron sputtering technique [9] and a typical ratio of 0.7 [3]. Recently, we changed to commercial films deposited by THEVA using the thermal co-evaporation technique [10] and found that the required ratio of is significantly different from that of the sputtered films.…”

“…However, there is a lower limit on the film thickness before film discontinuity occurs over the step. The most commonly Manuscript [3], [5], [7], [8]. The low value of 0.5 was used by Ma et al [7] to optimize their rf SQUIDs.…”

Measurement of Magnetic Nanoparticles Using High Transition Temperature Superconducting Quantum Interference Devices

“…These issues are exasperated when scaling YBCO sensors to cellular micrometer dimensions. Several fabrication techniques have been utilized in the past for high-T C SQUIDs such as grain boundary [10], ramp-edge [11], step edge [12] and ion irradiation [13], [14].…”