Development of REBCO Thin Films Using MOCVD on Non-Standard Buffers and Substrates

Rare Earth Barium Copper Oxide (REBCO) superconducting thin films on dielectric substrates are being developed for microwave and radio frequency applications such as transmission lines for quantum computing. Our group previously demonstrated the growth of REBCO thin films on short, flexible, yttria-stabilized-zirconia (YSZ) substrates. In this study, we report high-quality REBCO films on 12-cm-long flexible YSZ substrates. We planarized the surface of 40-µm-thick flexible YSZ substrate by vertical dip coating in n-propanol solution to achieve average surface roughness R _a<1 nm over 12 cm. We deposited a biaxially-textured magnesium oxide (MgO) template on a yttria seed layer using Ion Beam Assisted Deposition (IBAD) on flexible YSZ. Then, we deposited a 120-nm-thick MgO layer and a 120-nm-thick LaMnO₃ (LMO) cap layer. The out-of-plane and in-plane texture values of the LMO films were 3.9° and 6.9° respectively. REBCO films of a thickness of 350 nm were grown on these 12-cm-long flexible YSZ substrates by metal organic chemical vapor deposition (MOCVD) and a critical current density (J _c) of 1.06 MA/cm² was achieved at 77 K, 0 T. We are also developing an electrically conductive buffer architecture for defect-tolerant REBCO tapes, to shunt current from the REBCO film to substrate. This buffer architecture is based on conductive titanium nitride buffer on Hastelloy C276 substrate, with an oxide cap layer deposited by magnetron sputtering. REBCO films, about 350 nm thick, have been grown by MOCVD on this buffer architecture with a J _c greater than 1 MA/cm² at 77 K, self-field. Texture, microstructure, composition and critical current density of REBCO tapes on electrically conductive buffers will be presented.