Control of misfit strain in ferroelectric BaTiO₃ thin-film capacitors with SrRuO₃-based electrodes on (Ba, Sr)TiO₃-buffered SrTiO₃ substrates Available to Purchase

We investigate ferroelectric BaTiO₃ capacitors with SrRuO₃-based electrodes employing a (Ba_xSr_1−x)TiO₃ (BST) buffer layer on (100) SrTiO₃ substrates prepared by pulsed laser deposition. Structural analysis by high-resolution X-ray diffraction reciprocal space mapping shows that the BST (x = 0.5 and 0.7) layers are relaxed and have their bulk in-plane lattices in the upper part owing to strain relief. The bottom electrodes on the buffer layers grow heteroepitaxially but cannot withstand a tensile stress and then show a diminution of the in-plane lattice. On the BST (x = 0.7) layer, compared with the capacitor with an SrRuO₃ electrode, that with a Ba_0.1Sr_0.9RuO₃ one has a reduced in-plane lattice relaxation of the BaTiO₃ film and then exhibits a larger remanent polarization (P_r) of 34 μC/cm² associated with a smaller shift of the hysteresis loop. The polarization hysteresis shift is attributed to a flexoelectric effect stemming from the coupling between out-of-plane polarization and a strain gradient in the BaTiO₃ film. We conclude that a reduced misfit strain relaxation in the ferroelectric film achieved with the Ba_0.1Sr_0.9RuO₃ electrode on the thicker BST (x = 0.7) buffer layer is the origin of an enhanced P_r with a smaller hysteresis shift.