Periodic Reporting for period 1 - PerovSiC (Synergistic Resistive Switching of Perovskite and Silicon Carbide materials for Advanced ReRAM micro Devices)
Reporting period: 2017-07-01 to 2019-06-30
Perovskite oxides appear as strong candidates for the development of novel multilevel ReRAM switching devices, since they tolerate large variations in the oxygen content while maintaining their crystal structure. Currently, the ML storage properties of a number of perovskite materials and heterostructures has been successfully demonstrated. Despite the significant advances in perovskite-based ReRAM devices, the underlying RS mechanisms remain unclear and thus constitute a significant barrier to their widespread application . How to tune at best a perovskite resistive switch response or how to precisely control the size/resistance of the nanoscale defects causing the resistance change is still a critical challenge.
One of the major issues that this technology faces is to improve the reliability and stability of the MIM structure. The synthesis of perovskites demands high temperatures (typically above 500°C), which are incompatible with the thermal stability of metals. Metals suffer from quick thermal degradation, known as dewetting, in which agglomeration starts. The morphology of the metal evolves to a discontinuous and rough layer and finally breaks down into isolated particles, losing its functionality (breakdown of in-plane percolation) and leading to serious problems of device reproducibility and reliability. Up to know, the most adapted alternative is the use of an additional conductive oxide. However, this extra oxide film complicates enormously the study of the RS mechanisms, as it can contribute or modify the RS process through the mobility of O2- (or VO..). It is noteworthy to mention that TiN, which is also commonly used as conductive material, is not compatible with the synthesis of perovskites because it easily oxidizes from 450°C . Therefore, the development of new electrode-perovskite-electrode (EPE) structures which are thermally and chemically more stable, and which show an effective blocking to oxygen, is of great interest to control the RS of the functional layer and to be able to deeply investigate the RS mechanisms in perovskites.
The overall aim of the project is to move from fundamental studies of new EPE heterostructures based on perovskite thin films to their direct application as ML ReRAM devices, by:
1) Understanding of the nanoscale mechanisms governing the RS process.
2) Control, tuning and reproducibility of the RS behaviour.
3) Optimization of the RS response.
4) Demonstrating the effectiveness and application of the optimized EPE structures by designing and fabricating a reliable perovskite-based ML ReRAM device as a proof-of-concept.
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.
Finally, the project was promoted in the Science Festival, a national festival that takes place every year during a week in France. Finally, to enable a successful dissemination of the project a website was created.