Understanding of the microscopic mechanisms governing resistive switching in valence change memories (VCMs)

Among the various emerging devices expected to replace conventional Flash memories, Resistive Random Access Memories (ReRAM) are currently attracting a strong scientific and industrial interest. Their operations are based on the switching between a low resistive and a high resistive state, which represents the two binary states.
This PhD research project will focus on the understanding the microscopic mechanisms governing the resistive switching in pure and doped LaMnO3-δ oxides with perovskite-type structure, which will be studied as mixed ion-electron conducting memristive materials. Manganites such as LMO (LaMnO3-δ), LSMO (La1-xSrxMnO3-δ), PCMO (Pr1-xCaxMnO3-δ) and LPCMO (La0.325Pr0.3Ca0.375MnO3-δ) are among the most promising perovskite memristive materials reported in the literature, with On/Off ratios>103, operation speed down to 8 ns and endurance as large as 1010 cycles. Furthermore manganites such as La2/3Sr1/3MnO3-δ do not require an electroforming process, thus avoiding one of the major drawbacks for the implementation of memory devices based on RS phenomena. In addition, for this material the charge depletion effect is not only confined to the outermost surface layer, but its spatial extension and final HRS (high-resistance-state) can be modulated by the magnitude and duration of the potential applied, opening the door to the implementation of multilevel devices. The objective of this thesis is to acquire a better understanding of the nanoscale mechanisms governing the RS, charge carriers and interface effects in manganite-based ReRAM memories. This will be achieved by combining for the first time a unique set of complementary physical and chemical cutting-edge characterization methods, some of them enabling operando and spatially-resolved information. This knowledge is expected to lead to the design new nanostructured oxide films with tailored RS functionality and to the demonstration of the effectiveness and application of the optimized materials in reliable VCM memories with appropriate performance.

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