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Title: The fabrication of high temperature superconducting trilayer devices
Author: Bari, M. A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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In this research we have successfully developed a THS version of the Whole Wafer Process (WWP) to fabricate YBCO/PBCO/YBCO trilayer Josephson junctions using both c-axis and a-axis oriented single crystalline films. As in the case of LTS Niobium-based tunnel junction technology, the planar trilayer technology promises to be a good candidate for HTS electronics. Planar HTS Josephson junctions in the c-axis orientation are thought to be difficult to fabricate due to the low value of the coherence length in the c-direction (ξc~0.3 nm) compared to ξab~1.6 nm along the ab-planes. While on the other hand, a-axis oriented planar junctions are difficult to fabricate. Other limitations include the difficulty associated with depositing high quality trilayer structures with well defined interfaces. PBCO was chosen as the barrier material due to its structural and chemical compatibility with YBCO. This allowed epitaxial multilayered integration with YBCO. The first c-axis oriented trilayers were prepared by high pressure dc-sputtering using a range of barrier thicknesses. Josephson behaviour was observed in some junctions which showed RSJ-like current-voltage characteristics (CVCs), Shapiro steps and Fraunhofer-like magnetic modulation of the critical current. The differences in junction properties were found to be related to microstructure and surface morphology. Using off-axis laser ablation, high quality smooth and outgrowth free c-axis trilayers were obtained. The CVCs for junctions with a 60 nm thick PBCO barrier were hysteretic RSJ-like at low temperatures (<20 K). In addition to high IcRN products (8-18 mV), we observed an exponential dependent of RN with decreasing temperature indicating transport through a semiconducting-like PBCO barrier. The conductance spectra revealed a pronounced BCS-like gap feature at 2Δ=10.5 mV giving 2Δ/kBTc=1.3 which was found to be reproducible between different junctions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available