PREPARATION OF YBaCuO THIN FILMS ON VARIOUS SUBSTRATES BY LASER ABLATION

High-quality YBa2Cux0,_-6 films were prepared in situ by laser ablation on SrTiOs ( 100). on MgO ( 100) and on Si ( 111) + Zr02 buffer layer. We especially investigated the influence of the substrate temperature. In similar preparation circumstances zero resistivity has been achieved for films on SrTiOs up to 89.5 K, on MgO up to 84.6 K and on Si( +ZrOz) up to 83.5 K. X-ray diffraction analysis was used to study the growth conditions of the films, and to determine the oxygen stoichiometry. The films deposited at substrate temperatures above 720°C show pure c-axis orientation with an oxygen deficiency 6~ 0.1. Interdiffusion between substrate and layer, analyzed with Auger sputter profiling, could not be observed. The grains of the films on Si+ZrO,, studied by scanning electron microscopy, are caused by the polycrystalline buffer layer. These grains largely determine the physical properties of the deposited layer. Critical current measurements were carried out using wet chemically etched microbridges on the different substrates. At T= 77 K the values are in the range from 3 x lo6 A/cm’ for films on SrTiO, to 2x lo3 A/cm2 in the case of Si+ ZrOz. The extrapolated resistivity at T=O is found to be proportional to the temperature width of the superconducting transition.