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Face-to-Face Annealing of Bi2Sr2CaCu2O8+δ/MgO Precursor Films Fabricated by Metal–Organic Decomposition

To improve the uniformity of Bi2Sr2CaCu2O8+δ (Bi-2212)/MgO thin film, a face-to-face annealing method was introduced for a Bi-2212 precursor film (i.e., the surface of a precursor film was covered with that of another precursor film) fabricated by metal–organic decomposition (MOD). Compared with the Bi-2212 film fabricated by conventional single-substrate annealing, the coexistence of a Bi-2201 phase due to the thermal decomposition of Bi-2212 was drastically suppressed. The dominant rotation angle of the Bi-2212 film was η=45° ([100] of Bi-2212 ∥ [110] of MgO) and the full width at half maximum (FWHM) of the diffraction peak indicating η=45° became narrower with the face-to-face annealing. Moreover, a smooth surface with a grain size of approximately 10 µm was also observed. By improving the uniformity of the Bi-2212 phase and in-plane orientation, the critical current density at 4.2 K of the film fabricated by the face-to-face annealing became one order of magnitude higher than that of the film fabricated by conventional single-substrate annealing.