Freestanding GdBa ₂ Cu ₃ O _7−δ Thin Films via Optimized Buffer Layer Design: Preserving Superconducting Properties

Freestanding GdBa 2 Cu 3 O 7−δ (GdBCO) superconducting thin films were fabricated using a water-soluble Sr 3 Al 2 O 6 (SAO) sacrificial layer in combination with thermal release tape. An amorphous Al 2 O 3 capping layer was introduced to suppress crack formation during the lift-off process. The influence of buffer-layer design inserted between the GdBCO and SAO layers was systematically investigated with respect to structural integrity and superconducting properties after lift-off. A LaAlO 3 /SrTiO 3 bilayer buffer was found to be essential for maintaining epitaxial growth and a superconducting transition temperature ( T c ) of approximately 92 K after lift-off, comparable to that of the as-grown films. In contrast, a reversed SrTiO 3 /LaAlO 3 bilayer and single-layer buffer structures led to a suppression of T c, highlighting the critical role of stacking sequences. These results demonstrate that optimization of the buffer-layer design is a key factor for realizing high-quality freestanding GdBCO films while maintaining their superconducting characteristics.