Metalorganic chemical vapor deposition of lead-free ferroelectric BiFeO3 films for memory applications

Abstract

We have grown ${\mathrm{BiFeO}}_3$ thin films on ${\mathrm{SrRuO}}_3∕{\mathrm{SrTiO}}_3$ and ${\mathrm{SrRuO}}_3∕{\mathrm{SrTiO}}_3∕\mathrm{Si}$ using liquid delivery metalorganic chemical vapor deposition. Epitaxial ${\mathrm{BiFeO}}_3$ films were successfully prepared through the systematic control of the chemical reaction and deposition process. We found that the film composition and phase equilibrium are sensitive to the Bi:Fe ratio in the precursor. Fe-rich mixtures show the existence of $\alpha \text{-}{\mathrm{Fe}}_2{\mathrm{O}}_3$ , while Bi-rich mixtures show the presence of $\beta \text{-}{\mathrm{Bi}}_2{\mathrm{O}}_3$ as a second phase at the surface. In the optimized films, we were able to obtain an epitaxial single perovskite phase thin film. Electrical measurements using both quasistatic hysteresis and pulsed polarization measurements confirm the existence of ferroelectricity with a switched polarization of $110\text{–}120\mu \mathrm{C}∕{\mathrm{cm}}^2$ , $\Delta P(=P^{*}-P^{̂})$ . Out-of plane piezoelectric $\left(d_{33}\right)$ measurements using an atomic force microscope yield a value of $50\text{–}60\mathrm{pm}∕\mathrm{V}$ .