Inkjet-Printed Chemical Solution Y2O3 Layers for Planarization of Technical Substrates

The implementation of the Chemical Solution Deposition (CSD) methodology with the Drop on Demand (DoD) inkjet printing (IJP) technology has been successfully employed to develop a Solution Deposition Planarization (SDP) method. We have used nanocrystalline yttrium oxide (Y2O3) to decrease the roughness of technical metallic substrates by filling the surface imperfections and thus avoiding costly polishing steps. This alternative process represents an outstanding methodology to reduce the final cost of the second-generation coated conductors manufacturing. Two Y2O3 metalorganic precursor ink formulations were successfully developed and tested to obtain surfaces as smooth as possible with adequate mechanical properties to hold the internal stress developed during the growth of the subsequent layers. By using these inks as precursors for IJP and after a proper tuning of the rheological and wetting parameters, we firstly obtained centimeter length uniform 100 nm-thick SDP-Y2O3 films on unpolished stainless-steel substrate from Bruker HTS. The scalability of the roll to roll (R2R)-IJP process to 100 m is then demonstrated on metallic substrates as well. A complete characterization of the prepared SDP-Y2O3 inkjet-printed layers was carried out using optical microscopy, FIB-SEM (Focus Ion Beam coupled to Scanning Electron Microscopy), XRD (X-ray Diffraction), AFM (Atomic Force Microscopy), reflectometry and nanoindentation techniques. Then, the morphology, thickness, crystallinity and mechanical properties were evaluated, together with the surface roughness in order to assess the resulting layer planarity. The impact of planarity was additionally studied via growth of biaxially textured buffer layers as well as further functional layers. 1.1 μm-thick YSZ layers with in-plane textures better than the stainless steel (SS) polished reference were successfully deposited on top of 100 nm SDP-Y2O3 films yielding 50% of Ic in contrast to the standard SS reference.