Towards all-epitaxial lead-free metal-ferroelectric-metal heterostructures

Realizing metal-ferroelectric-metal heterostructures with atomically sharp and clean interfaces is a prerequisite for examining the full potential of thin film ferroelectric materials. Additionally, atomic layer control over the interfaces is crucial for tuning its ferroelectric properties with epitaxial strain. However, the premature loss of ferroelectricity due to inadequate stoichiometry control, the presence of dielectric dead layers, and dimensionality effects at the metal-ferroelectric interface is a long-standing challenge. We address the defect-controlled growth of the metal (SrRuO₃) and ferroelectric (BaTiO₃) layers with a metal-organic precursor-based hybrid molecular beam epitaxy (MBE) technique for both B-site cations. We observe an adsorption-controlled growth window for self-regulating stoichiometry in SrRuO₃ and BaTiO₃ films. We describe the effect of cationic flux ratios on SrRuO₃ properties such as surface morphology, electronic transport, and residual resistivity ratio (RRR). With this technique, we report a RRR = 87, the highest for coherently strained SrRuO₃ films grown on SrTiO₃ (001). Using all-epitaxial SrRuO₃/BaTiO₃/SrRuO₃ heterostructures, we will discuss the effect of stoichiometry, strain, and dimensionality on the dielectric properties of BaTiO₃ films.