Crystalline Texture Quality of Epitaxially Grown Bi ₂ Sr ₂ CaCu ₂ O _8+δ Superconducting Films for THz-on-a-chip Applications

High-quality growth of Bi2Sr2CaCu2O8+δ (Bi-2212) epitaxial films is still an interesting research topic for the development of novel high-Tc devices, particularly for scaling THz devices on a single chip. Among various growth techniques, the liquid-phase epitaxy (LPE) technique naturally enables the self-assembly of Bi-2212 epitaxial films at wafer scale. However, the LPE growth mechanism operates within a complexity of solid–liquid thermodynamic equilibrium maintained through stable conditions. Even under well-established protocols, this complex mechanism can be disturbed by process-induced instabilities such as precursor aging, material corrosion, solute accumulation, solvent evaporation, and surface crust formation. As part of a long-term research effort aiming at reliable growth for Bi-2212 films, we have first developed a compact motorized LPE prototype, engineered for precise control and stable maintenance of growth parameters. Under previously optimized conditions implemented into the LPE system, we successfully grew high-quality Bi-2212 epitaxial films. They exhibit a fully aligned film texture, allowing large-area continuous cleavage of the top Bi-2212 layers. This facilitates an in-depth investigation of the crystalline-texture quality across cross-sectional layers, with a focus on crystal disorder, impurity incorporation, and irregular grain nucleation. By systematically eliminating these process instabilities within the LPE mechanism, we evaluated the planar texture consistency and crystalline uniformity of the films and finally outlined the critical requirements of next-generation LPE system, capable of growing Bi-2212 films with large-grain epitaxial texture, which is highly suitable for THz-on-a-chip applications.