Development of REBCO Tapes on Non-Metallic Flexible Substrates for RF Applications

RE-Ba-Cu-O (REBCO, RE = rare earth) films on a flexible, low-cost, and low-thermal-expansion substrate offer a unique advantage for radio-frequency (RF) applications such as surface receiver coils for magnetic resonance imaging (MRI). Second-generation high-temperature superconductors (2G-HTS) are well developed for direct current (DC) applications. However, alternating current (AC) losses because of eddy currents in Hastelloy dominate at microwave frequencies. This work aims to develop REBCO on inexpensive and non-metallic flexible substrates for RF applications. Two methods have been developed in this work—exfoliation and transfer and direct growth. In the exfoliation and transfer method, the metallic substrate was peeled away from a standard 2G-HTS tape and the exfoliated REBCO film was transferred to a polyimide tape. Scanning Hall Probe Microscopy (SHPM) showed uniform trapped fields on the exfoliated tapes. For the growth method, polycrystalline, inexpensive, lightweight, and flexible yttria-stabilized zirconia (YSZ) with low thermal conductivity, low RF loss, and a relatively low dielectric constant was used as a substrate for epitaxial REBCO films. The YSZ substrate surface was planarized to a surface roughness Rq of about 1 nm, as measured by atomic force microscopy (AFM). Ion-beam assisted deposition (IBAD) was used to obtain highly-oriented single-crystalline-like buffer templates on planarized, polycrystalline YSZ substrates. Homo-epitaxial MgO and epitaxial LaMnO3 (LMO) thin films were deposited via reel-to-reel medium-frequency magnetron sputtering and radio-frequency magnetron sputtering, respectively. The out-of-plane and in-plane texture of homo-epitaxial MgO were optimized to 2° full-width-at-half-maximum (FWHM) and 5.5° FWHM, respectively. LMO out-of-plane and in-plane texture values were optimized to 2.6° and 6.8° FWHM, respectively. Epitaxial GdYBCO was grown by an Advanced Metal Organic Chemical Vapor Deposition (A-MOCVD) on the buffered-YSZ substrates with an in-plane texture average of ...