Evolution of Low Symmetric Phase in Strained Epitaxial (Ba0.5, Sr0.5)TiO3 Thin Films Grown on Si

Abstract

The evolution of low symmetric phases was investigated in epitaxial (Ba-0.5,Sr-0.5)TiO3 (BST) thin films grown on Si with yttria stabilized zirconia (YSZ). Paraelectric cubic BST thin films, when exposed to tensile strain primarily due to Si, present low symmetric phases, tetragonal c and monoclinic r phases, depending on the thickness of the BST thin films. When BST films are thin (<80 nm), BST thin layers are in a mixed state of r and c phases. As the thickness of the BST layers further increases, the c phase rapidly disappears, and the monoclinic r phase becomes predominant. These strained BST thin films exhibit non-zero polarization and manifest themselves by non-volatility in a metal-ferroelectric-insulator structure on Si, which is attributed to the non-cubic phases developed by strained BST thin films.