Improvement of Film Thickness Uniformity in TFA-MOD Coated Conductors☆

Abstract TFA-MOD process is expected to be promising for future applications since it can produce high performance YBCO coated conductors with low cost. The dip-coating is adopted as the coating process because of its simplicity and controllability of the overall film thickness. Dip-coated films have uniform thickness along longitudinal direction, but not necessary in transverse direction. In the case of thicker films, the more cracks form during processing at the thicker region near the edges generate and propagate mainly due to tensile and bending strain. So we have to suppress the thickness distribution in transverse direction for thicker films for high I C values. In this study, we found that the thickness distribution was firstly given by meniscus shape and then the solution flew down till it's dried. The solution in the center region drops more since it is slowly dried compared with the edge region. Then, we developed a drying process, which accelerates the drying by blowing hot gas to prevent the coated solutions from dropping. As a result, the thickness uniformity was improved; the thickness ratio of the thick region (edge) to the flat one (center) was improved from 1.35 to 1.07. Furthermore, we successfully produced ~1.5 μm thick films with high critical current density values (> 2MA/cm 2 ) by the new coating process including the force drying step.