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Fabrication and characterisation of multilayer test structures for coated conductor cylinder technology

Tanner, Joseph Leo (2010)
Ph.D. thesis, University of Birmingham.

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Abstract

The construction of a multi-layered, multi-turn coated conductor cylinder encompasses several aspects that may limit its performance unless they are designed and fabricated in a suitable way. This project investigates the optimum thicknesses of YBa$$_2$$Cu$$_3$$O$$_7$$$$_-$$$$_8$$ (YBCO) superconductor and SrTiO$$_3$$ (STO) insulator layers, interconnect design between YBCO layers and the fabrication process for defining tracks in the YBCO. Test samples were produced by pulsed laser deposition (PLD), photolithographic and ion-beam and chemical etching techniques and were characterised by AC susceptibility, transport measurements, atomic force microscopy (AFM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and x-ray diffraction (XRD). The growth conditions produce a YBCO film that develops a strong texture even over an ion-beam milled edge. Additional steps were required to remove contaminants from the surface after photolithographic processes, with both ion-beam milling and alkaline etch proving effective. Interconnects were successfully fabricated and were most effective when a large step was ion-beam milled into the first YBCO layer, rendering a critical current density (Jc) of 8.58x10$$^5$$A/cm$$^2$$. Electrical transport through a crossover was made possible by the application of an additional etching process to create a more gentle slope although further optimisation is required to improve epitaxial growth on the track edge.

Type of Work: Ph.D. thesis. Abell, J. S. and Button, Tim W Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Metallurgy and Materials TN Mining engineering. Metallurgy University of Birmingham 1282
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