The project has focused on evaluating the lanthanum manganite, LaMnO3 (LMO) in the thin film form, as a promising memristive material. LMO is able to accommodate a wide range of oxygen stoichiometry, which leads to changes in its electrical and mass transport properties. Different growth strategies by pulsed injection metal organic chemical vapour deposition (PI-MOCVD) have developed to fabricate a feasible LMO-based heterostructure compatible with mainstream microelectronics industry. The physicochemical properties of LMO films have investigated using standard, such as XRD, SEM, TEM, Raman, and EDX. After optimizing the deposition parameters, a set of samples combining LMO films with tuned oxygen content and several metals as top electrodes were micro fabricated using platinized-based silicon substrates. The main steps included were: (i) design the top electrodes in terms of geometry, size and material; (ii) optimize the microfabrication process, and (iii) electrical performance.
These devices were electrical characterized to validate the resistive switching. A filamentary behavior was found, which can be tuned to work in interfacial mode when applying low voltages and using active metallic top electrodes towards oxidation, such as Ti. Next, the physicochemical properties at the different resistance levels of LMO were investigated to understand the switching mechanisms, using cutting-edge techniques, such as ToF-SIMS, XANES, c-AFM and XPEEM. The movement of oxygen combined with the changes in the oxidation state of manganese were determined as drivers of the switching phenomenon. Based on all the findings, a comprehensive model was proposed describing the resistive switching mechanism at the nanoscale and linking both, the electronic and physicochemical changes occurring during the phenomenon. Finally, an optimized configuration was designed, fabricated, and tested as a stable multilevel ReRAM device prototype.
Figure: (a) SEM top-view image of a fully-dense and columnar polycrystalline LMO layer grown on the top of platinized substrates (Pt/TiO2/SiO2/Si) (b) Scheme of the LMO-based memristor prototype. (c-d) Hysteretic I-V switching curves for Ic= Is, for which symmetric switching was attained, and (e) for Is ³ Ic, for which asymmetric switching was attained; yielding to multiple resistance states in the same memory by operating in different electric field regimes. (f) XANES spectrum for the LMO pristine (highlighted by a blue line). Additional XANES spectra of extra LMO films with different oxygen content (d) have been added for comparing the position of the white line as function of d. (g) Operando XANES measurements performed under atmospheric conditions: signal intensity obtained before and after an in situ resistance change of factor two (see inset). A shift to higher energy values is observed for HRS, evidencing a volumetric reduction of Mn in this resistance state.
Type of action: MSCA-IF-EF-ST
Date of update December 20, 2019