This PhD thesis focuses on the study of the relationship between (La,Sr)MnO₃ (LSM) thin film’s microstructure and their functional properties in memristive devices. Valence Change Memories (VCMs), which rely on resistive switching phenomena, are exciting candidates for the next generation of non-volatile memories as they offer fast writing speed, high storage density and low power consumption. These memories store data in the form of a tunable resistance, which can be varied by an electrical stimuli. Typically, oxygen drift within the system provokes a redox reaction, which triggers the change of resistance. However, the VCMs performance is strongly related to the elements that compose the memory, i.e. active material, electrode and their interfaces.

In this thesis, the memristive response of La_1-xSr_xMnO₃ (LSM) perovskite oxide was studied in detail. LSM presents flexible oxygen stoichiometry accommodated through the change of Mn valence, which in turn modifies its electrical conduction properties. LSM thin films were successfully grown by pulsed-injection metal-organic chemical vapor deposition on three substrates to induce different microstructures: epitaxial films with low and high concentration of extended defects were grown on SrTiO₃ (STO) and LaAlO₃ (LAO) single crystals, respectively, and polycrystalline films with a large density of grain boundaries were grown on Si₃N₄ substrates. The memristive response was studied in micro-fabricated Ti/LSM\Pt planar devices. The formation of an oxygen deficient TiO_x interlayer at the Ti/LSM interface in pristine devices was observed by STEM. Moreover, X-Ray Absorption Near-Edge Spectroscopy measurements in a pristine device indicate a strong reduction of the Mn under the Ti electrode (Mn valence ca. +2.6) while the rest of the film was oxidized (valence ca. +3.5). The reduction of LSM suggests that, during the fabrication process the TiO_x is formed at the interface by scavenging oxygen from LSM.

First, the memristive performance was measured in the epitaxial samples, for which it was proven that the performance of the nanoionic devices can be boosted by microstructure engineering. Bipolar interface-type resistive switching was observed, where the transition to the high resistance state (HRS) or RESET was assigned to the drift of oxygen from LSM towards the Ti electrode (oxidizing it), while the reverse redox reaction leads to a low resistance state (LRS) via a SET process. The gradual oxidation/reduction can account for the multilevel resistance states measured in these devices. While the RESET takes place under similar conditions in LSM/LAO and LSM/STO, the SET process greatly depends on the microstructure of the LSM film. The high crystal quality of the LSM/STO epitaxial films seems to hinder the reincorporation of oxygen into LSM during the SET transition, and thus, asymmetric voltage operation is required, reaching a HRS/LRS ratio up to 7. On the other hand, in LSM/LAO devices where the extended defects act as fast migration paths to reincorporate the oxygen into LSM ,symmetric voltage operation is possible up to ±20 V with HRS/LRS up to 23.