Effect of post-annealing on thin YBCO films deposited from a nanocrystalline target

Pulsed laser deposition is used to ablate thin superconducting YBCO films o n SrTiO3 substrates. The most important parameters of thin superconducting films are high critical current density, ability to stand magnetic fields a nd smoothness of surfaces. Smoothness is important in fabrication of layere d structures and for research of basic properties of thin superconducting s tructures. The target sintered from YBCO nanopowder is a promising material for making films which meet most of the requirements above. Investigations by AFM show that our target has grains about one order of magnitude smalle r than usual grain size of commercial targets. At optimal deposition parame ters, the oxygen pressure of 0.4 torr in the chamber and the substrate temp erature 725 degrees C, films with T-c = 90 K, J(c) = 8 x 10(6) A/cm(2) (77 K) and RMS surface roughness = 1.5 nm are obtained. Thermal annealing of th e deposited films for 18 h at 900 degrees C further increases the value of J(c).