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

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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-μm-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 LaMnO3(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 (Jc) 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 theJcand surface resistivity of the REBCO films on a flexible YSZ substrate.