Structure-property relations for manganite memristive devices
Final Report Abstract
Manganite heterostructures show very promising resistive switching characteristics and multilevel resistance states. This makes them ideal candidates for alternative non-volatile memories, but also as building blocks for neuromorphic computation. The Mangaswitch project has been devoted to the study of resistive switching (RS) in strontium-doped lanthanum manganites (LSMO) with the aim of answering fundamental-science questions. The first goal of the project was to present a comprehensive and consistent picture of the ion transport properties of perovskite manganites. There are inconsistencies in the literature regarding bulk transport rates and activation enthalpies, and the behaviour at extended defects is poorly understood. Understanding the impact of such defects on the transport properties has allowed tuning its properties required for the application. In the project, we have moved from fundamental studies of model oxides (modelling and experimental work of LSMO films on single crystal substrates) to the application of these functional materials on silicon-based substrates, which can be used in the future as emerging data storage and logic circuit devices. High-quality, reproducible thin films of LSMO of two different doping concentrations (20% and 50%) were produced on single crystalline substrates (LaAlO3, SrTiO3, and SrTiO3 bicrystals) using pulsed laser deposition (FZJ) and metal organic chemical vapour deposition (LMGP). For both compositions, films were analysed for determination of their phase, composition, morphology, thickness and electronic properties. The ionic transport of oxygen was investigated by combining isotope exchange experiments with secondary ion mass spectrometry for bulk of both doping compositions and along dislocations generated within single crystalline films. In addition, molecular static and dynamics simulations were performed to investigate ionic transport in bulk phase and along similar dislocations. In addition, single crystalline (with and without dislocations) and polycrystalline thin films were used to fabricate resistive switching devices. Various device geometries using different electrodes were compared for both doping concentrations. Reproducible switching has been observed in vertical configuration using Pt/Al top-electrodes and SrRuO3 as bottom electrode, as well as in planar configuration with Pt/YSZ and Pt side contact, and with Pt/Ti and Pt electrodes. The modifications in the nanostructure of LSM (strain and dislocations) determine the memristive performance of interface-type Pt/Ti/LSM/Pt devices, leading to differences in cycle to cycle reproducibility and multilevel capabilities by the modification of the LSM’s oxygen migration properties. Cation vacancies, known to be present in high concentrations in the oxidising regime, have a detrimental effect on oxygen diffusivity. In addition, faster diffusion of oxygen along dislocations in perovskite manganites is explained as a space-charge phenomenon. The results we report show that nanostructure engineering is a promising approach for optimizing the performance of memristive devices, an approach which can also be extended to other nanoionic electrochemical devices.
Publications
- "The surprisingly high activation barrier for oxygenvacancy migration in oxygen-excess manganite perovskites", Phys. Chem. Chem. Phys., 2020, 22, 14329
J. M. Börgers and R. A. De Souza
(See online at https://doi.org/10.1039/D0CP01281E) - "Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space-Charge Phenomenon", Adv. Funct. Mater., 2021, 31, 2105647
J. M. Börgers, J. Kler, K. Ran, E. Larenz, T. E. Weirich, R. Dittmann and R. A. De Souza
(See online at https://doi.org/10.1002/adfm.202105647)
