Optimierung von gesputterten YBa_2Cu_3O_7_-_#delta#-Filmen fuer Hochfrequenzanwendungen

An apparatus for planar on-axis DC sputtering from stoichiometric targets under an oxygen pressure of a few hPa (high-pressure sputtering) was built up. In order to optimise the sputter technique for microwave applications and to investigate the microwave loss mechanism in sputtered epitaxial HTS films, about 400 YBa_2Cu_3O_7_-_#delta# or YbBa_2Cu_3O_7_-_#delta# films were grown on MgO, LaAlO_3, NdGaO_3 and YSZ substrates. The films were 10 x 10 mm"2 in size and 95-950 nm in thickness. The influence of the target, the HTS material (Yb instead of Y), the substrate, the substrate temperature, the oxygen pressure and the electrical environment of the substrate on the film quality was studied. The most reproducible film properties were achieved with phasepure, crackfree sputtertargets and a precisely controlled oxygen pressure of (2#+-#0,01) hPa during deposition. However, the strongest influence on the film quality was found for non-optimal deposition temperatures (optimal growth temperature: 715-765 C). Optimised Y(Yb)Ba_2Cu_3O_7_-_#delta# films exhibit T_c values between 88.5 and 92.5 K, critical current densities J_c (0.85 T_c) of 1-5.5 MA/cm"2 and low surface resistances (e.g. R_s (87 GHz) values of 0.3-5 m#OMEGA# and 8-20 m#OMEGA# at 4,2 K and 0,85 T_c), respectively. Furthermore, R_s of the best films is nearly independent on the microwave field level up to values of 24 mT and 9 mT respectively at 15 K and 77 K. (orig./MM)SIGLEAvailable from TIB Hannover: RO 9740(96-5) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Commission of the European Communities, Brussels (Belgium). European Programme for Research and Development in Information Technology (ESPRIT)DEGerman