A facile control of epitaxial-like barium strontium titanate thin films with various Ba/Sr ratios synthesized by a hydrothermal-galvanic couple method

Abstract

Barium strontium titanate (BaxSr1-xTiO3; BST) thin films exhibiting superior dielectric tunability have many technological applications. BST thin films with various Ba/Sr ratios were facilely produced on TiN-coated Si substrates by a hydrothermal-galvanic couple (HT-GC) method in mixed Ba(CH3COO)2 and Sr(CH3COO)2 alkaline solutions. A cubic single phase of BST films with the perovskite structure was obtained. Epitaxial-like growth in that strongly preferred (111) BST films grew over (111)-oriented TiN underlayer was observed for all the obtained films. When increasing the mole fraction of Ba2+ in the reaction solutions, the (111) diffraction peak of BST films shifted toward lower Bragg's angles, indicating a transition from Sr-rich to Ba-rich BST. From the X-ray photoelectron spectroscopy and electron probe for microanalysis, BST films with a full range of Ba/Sr ratios were obtained. The Sr ions were more readily incorporated into the films than Ba ions, which is associated with the lower formation energy of SrTiO3. Field-emission scanning electron microscopy revealed a spherical-particulate microstructure of the BST films. The formation mechanisms of the films by such a method were also discussed. The obtained BST films exhibited a promising dielectric tunability that could reach as high as 92%.