Electrical and microstructural degradation with decreasing thickness of (Ba, Sr)TiO3 thin films deposited by RF magnetron sputtering

The electrical degradation of (Ba,Sr)TiO3[BST] thin films as a function of the film thickness was investigated. BST thin films with various thickness were deposited on Pt/Ti/SiO2/Si substrates by in-situ RF magnetron sputtering. It was found that the electrical properties degraded markedly as the thickness of the films decreased. Electrical properties such as the leakage current and the dielectric constant are closely related to the surface morphology, in particular, the grain size of the films. The existence of an interfacial layer between the BST film and the Pt bottom electrode was confirmed by HRTEM. The interfacial layer appeared to have crystallinity different from both the BST thin film and the Pt bottom electrode which resulted in variation of the interfacial states between BST and Pt. As the thickness of the BST films decreased from 300 nm to 50 nm, the thickness of the interfacial layer increased from 9.5 nm to 11 nm. The dielectric constant of the interfacial layer calculated from its measured overall capacitance and thickness, confirmed by HRTEM, was about 30. This low-dielectric-constant interfacial layer has been shown to affect the electrical degradation of BST thin films with decreasing thickness.