2, Forschungszentrum Juelich GmbH, Juelich, , Germany
3, University Geneva, Geneva, , Switzerland
4, UAB, Bellaterra, , Spain
In recent years, huge efforts have been made in the research community to understand and control the Resistive Switching (RS) phenomena for applications ranging from Non-volatile memories to Neuromorphic computing. For instance, nonvolatile memories based on the RS effect, where two (or more) reversible resistance states can be induced upon application of an electric field, have emerged with excellent performance. On the other hand, RS phenomena have been used to emulate neurological functions of the brain and so it appears very appealing to correlate the RS mechanisms to materials properties in order to achieve full control of the electronic functionality thus enabling the design of new devices.
The RS phenomenon has been observed in many oxide systems, in particular in perovskite oxides, which are materials showing outstanding properties associated to the strong electronic correlation, such as metal-insulator transitions (MIT). This is the case of the metallic perovskite La1-xSrxMnO3 (LSMO), RENiO3 (RE=rare earth) and YBa2Cu3O7 (YBCO) family compounds, which are able to display Volume RS effects induced by the MIT and therefore, small changes in carrier concentration can induce huge resistance changes. The mechanism underlying this phenomenon is still unclear although oxygen vacancies mobility plays an key role in the mechanism underneath this phenomenon.
In this presentation we will discuss our studies on bipolar resistive switching of the mentioned perovskite oxides which were grown by Chemical Solution Deposition. Switching characteristics have been evaluated by C-SPM and I(V) curves with metal electrodes. Scanning tunneling microscopy and spectroscopy (STM/S), transport and resistive measurements were performed to gain insight into the local density of states of the material for different resistance states. Large resistance rations (102-104), over 100 cycle experiments, multilevel switching and switching dynamics have been evaluated. In addition, we have confirmed the strong influence of different atmospheres on the resistive switching properties of bare LSMO thin films. Remarkably, this influence disappears when the LSMO layer is capped with a CeO2 ultrathin layer grown by Atomic Layer Deposition, which acts as an oxygen reservoir, making this bilayer a proper material choice for encapsulation. A 3-terminal proof of principle device based on Ag/CeO2/LSMO/CeO2/Ag will be presented.
We believe that these results contribute to a better understanding of the physical mechanism behind the robust RS effect of these metallic perovskite oxides films which can be now considered for neuromorphic computing applications.