Growth of ${\rm MgB}_{2}$ Thin Films In Situ by RF Magnetron Sputtering With a Pocket Heater

We have grown MgB₂ thin films using RF magnetron sputtering combined with a pocket heater. This technique relies on a low-pressure environment for sputter deposition of boron and a high-pressure environment for thermal evaporation of Mg. We have obtained superconducting MgB₂ thin films using substrate temperatures of 480-540degC and Mg furnace temperatures of 730-750degC. The T_c onset of the thin films increased from 21.6 K to 35 K with increasing substrate temperature due to better crystallization. Higher boron deposition rates also increase T_c. The highest J_c of the films at 5 K and near zero magnetic field is 1.5 MA/cm² which is comparatively lower than the films grown using a pocket heater with boron deposition by chemical vapor deposition or electron beam evaporation. The chemical composition analysis by WDS exhibits a high concentration of oxygen and carbon in the MgB₂ films, which is due to a high background base pressure and an impure B sputtering target. These results suggest that the T_c, J_c, and resistivity of MgB₂ films are mainly determined by an inhomogeneous microstructure and superconducting percolation paths through impurity phases such as MgO. By comparison with carbon or oxygen doped films, the high impurity content in the sputtered MgB₂ films might act as method to achieve high H_c2.