Applications-Oriented Development of Buffer Architecture for REBCO Films on Nonmetallic Substrates

We have developed buffer architecture on a nonmetallic substrate with a length over 4 cm for epitaxial growth of a rare Earth barium copper oxide (REBCO) film. We used a 40- μ m-thick, flexible yttria-stabilized zirconia (YSZ) as a suitable nonmetallic substrate for high-frequency applications because of its good dielectric properties, low thermal conductivity, and flexibility. The YSZ substrate was planarized to ∼1 nm roughness, facilitating the growth of high-quality, biaxially-textured magnesium oxide (MgO) by ion beam-assisted deposition (IBAD) followed by magnetron-sputter-deposited homoepitaxial MgO and LaMnO ₃ (LMO) layers. The LMO films on flexible YSZ, with an out-of-plane texture of 3.1° and an in-plane texture of 6.7°, served as a good template for high-quality REBCO film growth. REBCO films of 350 nm thickness grown by metal–organic chemical vapor deposition were characterized using scanning hall probe microscopy for uniformity in critical current density ( J_c ) at 77 K. Surface resistivity values of the REBCO films on flexible YSZ at 8–8.3 GHz and 20–75 K were found to be on par with that of high-quality REBCO films on the sapphire substrate. An inverse correlation was found between the J_c and surface resistivity of the REBCO films on a flexible YSZ substrate.