Chemical solution derived planarization layers for highly aligned IBAD-MgO templates

The main goal of this research is to develop a chemical solution derived planarization layer to fabricate highly aligned IBAD-MgO templates for the development of high temperature superconductor (HTS) based coated conductors. The standard IBAD-MgO template needs an additional electrochemical polishing step of the mechanically polished 50 μm-thick Hastelloy C-276 substrates to ensure a flat and smooth surface for subsequent growth of multi-layer buffer architectures, which include: sputtered 80 nm Al₂O₃; sputtered 7 nm Y₂O₃; IBAD 10 nm MgO; sputtered 30 nm homo-epi MgO; and sputtered 30 nm LaMnO₃ (LMO) layers. We have successfully developed a solution planarization layer that removes the electrochemical polishing step and also acts as a barrier layer. Crack-free, smooth Al₂O₃ layers were prepared on mechanically polished Hastelloy substrates using a chemical solution process. The average surface roughness value, R_a, for a starting substrate was 9-10 nm. After eight coatings of Al₂O₃ layer, the R_a was reduced to 2 nm. Highly aligned IBAD-MgO layers with out-of-plane and in-plane textures comparable to the standard IBAD-MgO layers were successfully deposited on top of the solution planarization Al₂O₃ layers with an Y₂O₃ nucleation layer using a reel-to-reel ion-beam sputtering system. Both homo-epi MgO and LMO layers were subsequently deposited on the IBAD-MgO layers using RF sputtering to complete the buffer stack required for the growth of HTS films. YBa₂Cu₃O₇-δ (YBCO) films with a thickness of 0.8 μm deposited on these IBAD-MgO templates by pulsed laser deposition showed a high self-field critical current density, J_c, of 3.04 MA cm^-2 at 77 K and 6.05 MA cm ^-2 at 65 K. These results demonstrate that a low-cost chemical-solution-based, high-throughput Al₂O₃ planarization layer can remove the electro-polishing step and replace sputtered Al₂O₃ layers for the production of high J_c YBCO-coated conductors.