Double gun off-axis sputtering of large area YBa2Cu3O7-δ superconducting films for microwave applications

In order to extend earlier work on in-situ off-axis sputtering to larger areas, the authors used two facing targets in the off-axis configuration to produce YBa₂Cu₃O_7-δ superconducting films with low microwave surface resistance on 5-cm-diameter LaAlO₃ substrates. Surface resistance (R_s ) values at 10 GHz of 40±10 μΩ at 4.2 K and 400±100 μΩ at 77 K, superconducting transition temperatures of over 89 K, and thickness variations of less than ±8% are uniformly obtained over the entire 5-cm-diameter area. The authors also report a detailed characterization of the electronic and structural properties of the films produced on the LaAlO₃ substrates for a wide range of growth conditions. The influence of YBCO microstructure on the transport properties and the effect of magnet geometry in the two sputter guns are also discussed. It is concluded that in-situ off-axis sputtering from two facing targets can reproducibly fabricate very-high-quality YBCO films with low microwave surface resistance over large areas. The thickness uniformity over large areas is greatly enhanced over single-target sputtering by using this technique