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

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