Metalorganic Chemical Vapor Deposition of REBCO on Various Substrates and Correlation of its Superconducting properties for High Frequency and Functional Applications

Rare Earth Barium Copper Oxide (REBCO, RE-Ba2Cu3O7-δ) coated conductors (CC) are the only superconductors with a potential for direct current (DC) applications over broad range of temperature (77 K – 4.2 K) and wide range of magnetic fields (0 – 20 T). This makes them representative in various domains such as Power, Energy, and Medicine. In the electrical power domain, they are utilized in power cables, transformers, generators, and motors. A high critical current density (Jc) of REBCO CC can be leveraged to generate strong magnetic fields, opening up pathways for use in high-energy particle accelerators, nuclear fusion reactors, superconducting magnetic energy storage devices and MRI magnets.
Development of long length REBCO CC is demonstrated using a Pilot A-MOCVD tool utilizing ohmic heating. Critical Currents (Ic) > 1000 A/12mm @ 77 K over 50 m length with film thickness of 4μm, in a single pass has been achieved. A key feature of the Pilot A-MOCVD setup is inline monitoring by 2D-XRD. Crystallographic structure and Jc correlations & predictions has been devised to provide process feedback. Additionally, an investigation using General Area Detector Diffraction System (GADDS) in predicting the film composition, lattice strain, and superconducting properties of 5% Zr-doped REBCO thin films is conducted with the aim of practical applications.

Apart from DC applications, REBCO can be used in microwave applications owing to its low surface resistance (Rs). Applications such as resonators, microstrip-lines, microwave circuits, band-pass filters, radiation detectors and superconducting quantum interference devices (SQUID) fall into this category. To curtail losses at radio frequency (RF), it is critical to grow REBCO over dielectric substrates rather than metallic substrates as in CC. REBCO growth over one such substrate Y2O3-stabilized ZrO2 (YSZ) using MOCVD is demonstrated. Superior Q-factor of >44000 (@ 25 K, 9.4 GHz) and Jc > 1 MA/cm2 (@77 K) have been achieved. Homogeneous REBCO growth was confirmed using scanning hall probe microscopy (SHPM) over sample length with uniformity in Jc <15%. Key MOCVD process parameters such as heater susceptor temperature, precursor composition and residual oxygen concentration have been optimized. Crystallographic texture of the fabricated films was assessed by 2D-XRD. Composition of the REBCO films was determined using inductively coupled plasma mass spectrometry (ICP-MS) and optimum superconducting performance was observed near a composition of Ba/Cu = 0.72.