MBE growth of large area RE-123 superconductor thin films for microwave applications

Large area high quality epitaxial thin films are required for many commercial microwave applications of high temperature superconductors. Although there exists different techniques for the growth of high temperature superconductor films, molecular beam epitaxy (MBE) growth has the advantage of achieving better homogeneity and scalability. We have succeeded in growing high quality RE-123 (RE=La, Nd, Eu, Gd, Dy) superconductor films by MBE. The growth of high quality films by MBE requires strict compositional control and optimization of growth temperature and oxidation conditions. Strict compositional control is the most vital in achieving best characteristics of the films and we have found that composition close to 123 yields the best results. By optimizing the different growth parameters, we have grown high quality RE-123 films with high T_C(0) & J_C, low resistivity and low microwave surface resistance. Among the different RE-123 films we have investigated so far, Nd-123 superconductor films shows the better characteristics. Nd-123 films grown on (100) MgO under optimized conditions gave a T_C(0) of 94 K with a J_C above 3.5 MA/cm² at 77 K. These Nd-123 films show excellent metallicity (ρ_{300 K}/ρ_{100 K}∼3) with room temperature resistivity of ∼140 μΩ.cm. The films had excellent in-plane orientation and high crystallinity. The MBE grown Nd-123 films show low microwave surface resistance (∼870 μΩ at 77 K @ 22 GHz) making them better candidate for microwave applications.