Structural, Optical and Electrical Characteristics of Low Temperature Grown BaSrTiOx Thin Films

Among several perovskite oxides BaSrTiOx (BST) thin films have attracted a great interest for their potentials in oxide-based electronics. However, their reliability and efficiency depend strongly on the precise knowledge of microstructure, as well as optical and electrical constants. In the present work, BST films were deposited using radio frequency magnetron sputtering technique on UV fused silica and Si substrates at room temperature. The dependences of film microstructure, surface morphology, absorption edge, refractive index, and dielectric constants on deposition pressure, partial oxygen flow and the post-deposition annealing were examined by grazing-incidence X-ray diffraction, scanning electron microscopy, spectrophotometry, ellipsometry, as well as photoluminescence, capacitance-voltage and current-voltage measurements. Well-adhered, uniform and amorphous films were prepared at room temperature. For all as-deposited films, the average optical transmission was ~85% in the visible and near infrared spectrum. The refractive indices of BST films were in the range of 1.90 to 2.07 (λ = 550 nm) as a function of deposition conditions. Post-deposition annealing at 800 oC for 1 hr produced polycrystalline films, increased refractive indices and dielectric constants but considerably lowered film optical transmission. Frequency dependent dielectric constants were found to be 46-72, and the observed leakage current was very small ~1A. Initial results revealed that low-temperature-grown BST thin films have promising properties for device applications.