Robust polarization switching behavior in metal-organic MBE-grown metal-ferroelectric-metal heterostructures

The reliability of thin-film metal-ferroelectric-metal devices depends on the degree of control in the synthesis of each constituent layer and the atomic sharpness of the metal-ferroelectric interfaces. While lead-based perovskite oxide ferroelectrics such as PZT and PMN-PT are leading contenders in some of these devices, the toxicity of lead has prompted a renewed interest in lead-free ferroelectrics within the perovskite oxide family. Using metal-organic molecular beam epitaxy (MBE) to meet these synthesis prerequisites, we grow phase-pure, epitaxial, single-crystalline BaTiO₃ on SrRuO₃-buffered SrTiO₃ (001) substrates. We note robust polarization switching with piezoresponse force microscopy for an applied bias of ± 6 V for a ~ 36 nm BaTiO₃ film without any post-growth oxygen annealing. We extend this technique to grow SrRuO₃/BaTiO₃/SrRuO₃ heterostructures on Nb-doped SrTiO₃ (001) substrates. For a ~ 40 nm BaTiO₃ layer, we observe a room-temperature static dielectric constant of ~ 400 and ideal capacitor-like behavior up to 1 kHz using impedance spectroscopy. We demonstrate hysteretic P-E curves with a P_r ~ 17 µC cm^-2 and an E_c ~ 221 kV cm^-1 at f = 1 kHz. We will discuss the effect of stoichiometry, post-growth annealing, strain, and dimensionality on the structural and dielectric properties of metal-organic MBE-grown ferroelectric oxides.