Domain structures induced by tensile thermal strain in epitaxial PbTiO3 films on silicon substrates

Abstract

The fabrication of epitaxial ferroelectric materials on Si substrates is key to the design of superior ferroelectric devices for applications involving microelectromechanical systems (MEMS). The domain structures of epitaxial PbTiO3 films grown on Si substrates with an epitaxial SrTiO3 buffer layer were investigated, especially in terms of film thickness dependence. The low thermal expansion coefficient of Si was found to affect the volume fraction of (001)-oriented domains not only in relatively thick film regions but also in the thinner ones. Compared with the PbTiO3 films deposited on SrTiO3 substrates, (100)-oriented domains were observed in films as thin as 18 nm, notwithstanding the strong misfit strain induced by the substrate. Moreover, the saturated volume fraction of the (001)-oriented domain was smaller than that of PbTiO3 on SrTiO3. Thermal strain plays a critical role in determining domain structures and is, therefore, expected to govern the electric properties of films useful in MEMS devices.