Microstructure and electrical properties of Ba1 − xSrxTiO3 thin films prepared by rf magnetron sputtering

Barium strontium titanate (BaxSr1 − xTiO3, BST) films were prepared by rf magnetron sputtering with the substrate temperature ranging from 25 to 550 °C and were investigated by transmission electron microscopy (TEM) equipped with an energy dispersive spectroscopy (EDS), field-emission scanning electron microscopy (FE-SEM), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). Electrical characteristics of the BST was evaluated with the films deposited on the Pt/Ti/SiO2/Si multilayered substrate. It is found that the film deposited at substrate temperature 25 °C is amorphous, whereas that deposited at substrate temperature 450 °C is a mixture of crystalline and amorphous phases, in which small crystallites are dispersed near the surface of the film. In contrast, the film deposited at substrate temperature 550 °C shows a columnar structure with 20-50 nm in column size. It is likely that the crystallinity of the BST films depends upon the stoichiometric composition of the film. Measurement of electrical properties shows that the dielectric constant of BST increases with the crystallinity and grain size of the films. It is also obtained that the leakage current density is closely related to the microstructure of the BST films, but is nearly independent on the surface morphology of the films.