Relation between electrical properties and microstructure of YBa2Cu3O7−x thin films deposited by single-target off-axis sputtering

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Abstract
The relationship between the deposition conditions and the structural and electrical properties of in situ superconducting YBa2Cu3O7−x thin films deposited by off-axis magnetron sputtering has been investigated. High-quality films have been produced with a transition temperature TC (R=0) of 92 K, a critical current density JC (zero field) of 3.3×107 A/cm2 at 4.2 K and 4.8×106 A/cm2 at 77 K, and a microwave surface resistance RS of 2.6×10−6 Ω at 1.5 GHz and 4.2 K which rises to 8.3×10−6 Ω at 77 K. Among the deposition conditions explored, substrate temperature was identified as the most influential in producing these high-quality films. A quantitative relationship was established between substrate temperature and TC, normal-state resistivity ρ, JC, orientation distribution, x-ray-diffraction peak broadening, lattice expansion, RS, and penetration depth λ. Increasing substrate temperature results in an increase in TC, a decrease in ρ, an increase in JC, an increase in grain size, an increase in the ratio of c-axis- to a-axis-oriented grains, and a decrease in λ. The deposition conditions of high substrate temperature and oxygen pressure, used to form films of the highest electrical and structural quality, also promote the formation of CuO precipitates of about 1 μm in dimension, resulting from a slightly copper-rich stoichiometry.