Analysis of a DC sputtering process for deposition of epitactic YBa2Cu3O7-δ films on dielectric and metal substrates

The planar DC-sputtering as a preparation process for epitaxial YBCO films on monocrystalline and textured substrates is investigated. For a reproducible deposition of YBCO films with a thickness d up to 1 μm the substrate temperature has to be kept constant. Films deposited in this way on MgO and LaAlO3 show an intrinsic decrease of Jc(0.85 Tc) with 1/√(d). In measurements on diameter 2 inch films Tc values of 89.5 K and Jc(77 K) values of 4.4 MA/cm2 were obtained in average on an area of diameter = 35 mm. Maps of the Jc distribution indicate a decrease in Jc at the edge of the substrate caused by the shape of the plasma. The values of the surface resistance Rs(4.2 K) and Rs(77 K) measured at 19 GHz are in the range of 0.2 and 1.2 mΩ and remain constant up to surface magnetic fields of 30 and 5 mT respectively. XRD- and TEM-analysis indicate also a good crystalline structure. A double-sided deposition with the high-pressure DC-sputtering is only possible step-by-step. The superconducting properties of the a- and b-side are nearly the same as for one-sided films. However, the side deposited first is often slightly degraded after the rear side deposition showing a worse crystalline quality and contaminations. The use of a radiation heater also allows a successful HTS deposition on metallic substrates. For this the control of the growth temperature is essential. YBCO films grow epitaxially on cube-textured, CeO2-buffered Ni tapes, but their superconducting properties are still limited because of grain boundaries and cracks within the buffer and the HTS layer. Values of the critical current densities in the range of 0.3 MA/cm2 at 63 K and 0.1 MA/cm2 at 77 K were achieved up to now. (orig.)