Recently, the critical current properties of REBa2Cu3O7-δ (RE123, RE = rare-earth and Y)-coated conductors (CCs) have been remarkably improved. As a result, the time for applying CCs has arrived. One of the major applications of CCs is power devices such as transmission cables, transformers, etc. Since power devices commonly operate using alternating current (AC), it is necessary to reduce AC loss. The other major application of CCs is their use in magnetic coils. In this case, it is important to reduce the effect of shielding current arising from the natural characteristics of Type-II superconductors; especially for magnet applications with high homogeneity and magnetic-field stability, such as magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) and medical accelerator coils. For these purposes, it is well known that with low-temperature superconducting wires and tapes the multi-filamentary structure is indispensable. In this paper, the approaches to fabricating multi-filamentary CCs are reviewed based on information reported by various research institutions.
