Dielectric Properties and Microstructures of Ba 1−x Sr x TiO 3 Epitaxial Thin Films with Compositional Gradients Normal to the Substrates

Abstract

The characterizations of microstructures and dielectric properties of epitaxial Ba 1 m x Sr x TiO 3 (0.0 h x h 0.25) (BST) thin films with compositional gradients normal to the substrates are reported. The compositionally-graded BST films with increasing x from 0.0 to 0.25 were deposited layer-by-layer on MgO (100) single-crystal substrates by pulsed laser deposition. X-ray diffraction, rocking curve, and φ scans showed that the graded films are epitaxial growth with (100) BST //(100) MgO . Surface morphologies of the graded BST films were examined by atom force microscopy. Compositional distributions across sections of graded BST films were characterized by Rutherford backscattering spectrometry. The dielectric constant and dielectric loss of the graded BST films measured at 10 kHz by vertical structures using LSCO as bottom electrodes, were 715 and 0.0103, respectively. The graded BST films exhibit a broad and flat profile of the dielectric constant versus temperature. Such behavior of the dielectric response is attributed to the presence of the compositional and/or residual strain gradients in the epitaxial graded films. With such graded structure, it is possible to build a dielectric thin film capacitor with a low temperature dependence of the capacitor over a broad temperature range.