Optimization of high‐quality YBa ₂ Cu ₃ O _{7‐ <i>δ</i>} superconducting nanowire fabrication by post‐thermal annealing

Abstract The fabrication of high‐quality YBa 2 Cu 3 O 7− δ (YBCO) nanowires has garnered significant attention in the field of high‐temperature superconductivity due to their potential applications in quantum communication, deep space exploration, and various other fields. Cl 2 ‐assisted reactive ion etching (RIE) stands out as a more effective and efficient method for patterning scalable thin films. However, neither RIE nor high‐density RIE has achieved superconducting YBCO nanowires with a width smaller than 3 μm. Here, we delve into the factors that limit the line width of Cl 2 ‐assisted inductively coupled plasma reactive ion etching (ICP‐RIE) processing and the method to elimiate them. Our approach involves utilizing Cl 2 /Ar as etching gas and incorporating a specialized vacuum heating process after etching. Our experimental results demonstrate the successful realization of 10 nm‐thick YBCO nanowires with widths as small as 0.15 μm, exhibiting excellent performance in terms of their intrinsic superconducting properties. The mechanism is evidenced by X‐ray photoelectron spectroscopy (XPS) analysis in comparison of nanowires with and without heating treatment, in which the residual Cl 2 on the sidewall of nanowires evaporates and oxidizes Cu + back into Cu 2+ in an unetched state.