Preparation and Properties of Laser Deposited High Tc Films

Abstract

High Tc superconductor films were prepared by laser deposition using a SIEMENS XP 2020 excimer laser. Epitaxial YBaCuO films of high quality are obtained for a uniform laser beam energy density of about 4 J/cm2, a substrate temperature above 730 °C and an oxygen pressure of about 0.4 mbar. These films show high DC critical current densities as 5×106 A/cm2 at 77 K or 6×107 A/cm2 at 4.2 K and zero field and excellent microwave properties as surface resistance or attenuation constant. The performance of first passive microwave devices made from these films will be discussed. Using identical parameters, LaAlO3 inter-layers grow epitaxially on the YBaCuO films and are therefore used as insulating layers in multilayer structures. Also epitaxial Bi2Sr2CaCu2Ox films were prepared on SrTiO3 substrates. The inductively measured Tc,onset reached 83 K. Critical current densities up to 107 A/cm2 at 4.2 K and 106 A/cm2 at 50 K were obtained. In magnetic fields, these films show a dramatic dependence on the field direction, with jC being almost field-independent (up to 7 T) at low temperatures, when the field lies within the film plane.