Growth of (Ba,Sr)TiO3 Thin Films by MOCVD: Stoichiometry Effects

(Ba_xSr_1−x)TiO₃ thin films were deposited in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system using 0.35 molar solutions of Ba(thd)₂ and Sr(thd)₂ and a 0.4 molar solution of Ti(O-i-Pr)₂(thd)₂. The film growth on Pt-(111) was investigated within a wide parameter field, e.g., the deposition temperature was varied between 560°C and 650°C, which yields films with microstructures ranging from randomly oriented polycrystalline to perfectly (100)-textured columnar structures. Special emphasis is given to film stoichiometry: starting with (Ba_0.7Sr_0.3)TiO₃ the Group-II/Ti content was varied from 0.9 to 1.1 and the Ba content was reduced to the limit of pure SrTiO₃ films. The electrical properties of MIM structures were investigated after deposition of Pt top electrodes. The nominal thickness of the films was varied between 5 and 100 nm and permittivity and leakage current both are shown to depend strongly on the film thickness. These dependencies on the film thickness are analyzed within the phenomenological dead layer model. The dependence of the electrical properties on stoichiometry are discussed in detail.