Growth quality and critical current density of sputtered YBaCuO thin films

Thin YBaCuO films have been deposited onto single crystalline substrates (Al₂O₃, MgO, SrTiO₃, Zr(Y)O₂) by inverted cylindrical magnetron sputtering. The growth quality of the films has been studied by X-ray diffraction and channelling experiments. Single crystalline growth has been achieved on (100) oriented substrates (MgO, SrTiO₃, Zr(Y)O₂) characterized by the occurrence of the channelling effect with minimum yield values, χ_min, below 10% and narrow rocking curves (ΔΨ < 1°) in the diffraction experiments. Maximum critical current density values, j_c, in zero field of 5 × 10⁶, 2 × 10⁶, and 9 × 10⁵ A cm^-2 at 77 K have been measured for films on SrTiO₃, Zr(Y)O₂ and MgO, respectively. On randomly orientated Al₂O₃ and Zr(Y)O₂ the films grow textured but are principally polycrystalline, resulting in depressed j_c values of 5 × 10³ and 5 × 10⁵ A cm^-2. With decreasing film thickness, d, high j_c values (2 × 10⁶ A cm^-2, 77 K) are observed down to d = 30 nm for films on SrTiO₃. In ultrathin films (d = 5 nm) j_c degraded (e.g. 3.5 × 10⁵ A cm^-2, 4.2 K) but revealed a magnetic field dependence quite different from that for thicker films. In particular, almost no depression of j_c was observed in a parallel field of up to 13 T.