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SrFeOx resistive switching memory devices based on brownmillerite with an oxygen vacancy channel exhibit high durability and fast performance. In particular, a high on/off ratio of > 104 was observed when Nb-doped SrTiO3 was used as the bottom electrode. We studied a SrFeOx/Nb-doped SrTiO3 (111) device with a high on/off ratio, and used in-situ transmission electron microscopy to examine the crystalline structures of the SrFeOx layer in the high and low resistance states. We employed electron energy-loss spectroscopy to determine oxygen redistribution near the interface between the SrFeOx structure and Nb-doped SrTiO3. The resistance increased when oxygen vacancies accumulated at the interface between Nb-doped SrTiO3 and perovskite SrFeO3−δ, and decreased when oxygen ions filled the interface. In contrast, we observed little change in the oxygen concentration at the interface between Nb-doped SrTiO3 and brownmillerite SrFeO3−δ. We show that the resistance of the SrFeOx/Nb-doped SrTiO3 (111) device is mostly concentrated at the interface between the perovskite SrFeO3−δ and Nb-doped SrTiO3, which changes the barrier height. [ABSTRACT FROM AUTHOR]

Manipulation of the heterointerfacial structure and/or chemistry of transition metal oxides is of great interest for the development of novel properties. However, few studies have focused on heterointerfacial effects on the growth characteristics of oxide thin films, although such interfacial engineering is crucial to determine the growth dynamics and physical properties of oxide heterostructures. Herein, we show that heterointerfacial effects play key roles in determining the growth process of oxide thin films by overcoming the simple epitaxial strain energy. Brownmillerite (SrFeO2.5; BM-SFO) thin films are epitaxially grown along the b-axis on both SrTiO3(001) and SrRuO3/SrTiO3(001) substrates, whereas growth along the a-axis is expected from conventional epitaxial strain effects originating from lattice mismatch with the substrates. Scanning transmission electron microscopy measurements and first principles calculations reveal that these peculiar growth characteristics of BM-SFO thin films originate from the heterointerfacial effects governed by their distinct interfacial structures. These include octahedral connectivity between dissimilar oxides containing different chemical species and a peculiar transition layer for BM-SFO/SrRuO3/SrTiO3(001) and BM-SFO/SrTiO3(001) heterostructures, respectively. These effects enable subtle control of the growth process of oxide thin films and could facilitate the fabrication of novel functional devices. [ABSTRACT FROM AUTHOR]

We had discovered novel resistance switching phenomena in SrCoOx epitaxial thin films. We have interpreted the results in terms of the topotactic phase transformation between their insulating brownmillerite phase and the conducting perovskite phase and the existence of a rather vertical conducting filament due to its inherent layered structure. However, the rough interface observed between the SrCoOx and the Au top electrode (area ~10000 μm2) was assumed to result in the observed fluctuation in key switching parameters. In order to verify the effect of rough interface on the switching performance in the SrCoOx device, in this work, we studied the resistive switching properties of a SrCoOx device by placing a Au-coated tip (end area ~0.5 μm2) directly on the film surface as the top electrode. The resulting device displayed much improved endurance and showed high uniformity in key switching parameters as compared to the device having a large top electrode area. A simulation result confirmed that the Au-coated tip provides a local confinement of the electrical field, resulting in confinement of oxygen ion distribution and therefore localization of the conducting filament. By minimizing other free and uncontrollable parameters, the designed experiment here provides the most direct and isolated evidence that the rough interface between electrode and ReRAM matrix is detrimental for the reproducibility of resistivity switching phenomena. [ABSTRACT FROM AUTHOR]