STUDIES ON STRUCTURAL AND ELECTRICAL-PROPERTIES OF BARIUM STRONTIUM-TITANATE THIN-FILMS DEVELOPED BY METALLOORGANIC DECOMPOSITION

Thin films of barium strontium titanate (BST) including BaTiO3 and SrT iO3 end members were deposited using the metallo-organic decomposition (MOD) technique. Processing parameters such as nonstoichiometry, anne aling temperature and time, film thickness and doping concentration we re correlated with the structural and electrical properties of the fil ms. A random polycrystalline structure was observed for all MOD films under the processing conditions in this study. The microstructures of the films showed multi-grains structure through the film thickness. A dielectric constant of 563 was observed for (Ba0.7Sr0.3)TiO3 films rap id thermal annealed at 750 degrees C for 60 s. The dielectric constant increased with annealing temperature and film thickness, while the di electric constant could reach the bulk values for thicknesses as thin as similar to 0.3 mu m. Nonstoichiometry and doping in the films resul ted in a lowering of the dielectric constant. For near-stoichiometric films, a small dielectric dispersion obeying the Curie-von Schweidler type dielectric response was observed. This behavior may be attributed to the presence of the high density of disordered grain boundaries. A ll MOD processed films showed trap-distributed space-charge limited co nduction (SCLC) behavior with slope of similar to 7.5-10 regardless of the chemistry and processing parameter due to the presence of main bo undaries through the film thickness. The grain boundaries masked the e ffect of donor-doping, so that all films showed distributed-trap SCLC behavior without discrete-traps. Donor-doping could significantly impr ove the time-dependent dielectric breakdown behavior of BST thin films , mostly likely due to the lower oxygen vacancy concentration resulted from donor-doping. From the results of charge storage density, leakag e current and time-dependent dielectric breakdown behavior, BST thin f ilms are found to be promising candidates for 64 and 256Mb ULSI DRAM a pplications. (C) 1997 Elsevier Science S.A.