Mechanism for bipolar resistive switching in transition metal oxides M. J. Rozenberg, 1, 2 M. J. S´ anchez, 3 R. Weht, 4, 5 C. Acha, 2 F. Gomez-Marlasca, 4 and P. Levy 4 $^{1}$Laboratoire de Physique des Solides, UMR8502 Universit´ e Paris-Sud, Orsay 91405, France $^{2}$Departamento de F´ısica J. J. Giambiagi, FCEN, Universidad de Buenos Aires, Ciudad Universitaria Pab. I, 1428 Buenos Aires, Argentina $^{3}$Centro At´ omico Bariloche and Instituto Balseiro, CNEA, 8400 - San Carlos de Bariloche, Argentina $^{4}$Gerencia de Investigaci´ on y Aplicaciones, CNEA, 1650 - San Mart´ın, Argentina $^{5}$Instituto Sabato, Universidad Nacional de San Mart´ın-CNEA, Argentina We introduce a model that accounts for the bipolar resistive switching phenomenom observed in transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces, leading to a spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce non-trivial resistance hysteresis experiments that we also report, providing key validation to our model. PACS numbers: 73.40.-c, 73.50. -h There is a great deal of experimental activity currently devoted to explore new technologies for the next gen- eration of electronic memory devices $^{1}$. Among various promising options, the resistive random access memory (RRAM), which is based on the resistive switching (RS) phenomenon, has emerged as a preeminent candidate $^{2,3}$. The RS effect is a large, reversible and nonvolatile change in the resistance after the application of voltage or cur- rent pulses. The typical RRAM system has a capacitor- like structure composed of insulating or semiconducting materials sandwiched between two metal electrodes. RS has been observed in a wide variety of systems, such as simple and complex oxides, organic compounds, etc $^{3,4}$. However, there are specific characteristics of the switch- ing behavior observed in each type of material. In the case of binary oxides, which are highly insulating it is believed that the RS effect may be due to the formation and rupture of conductive filaments within the insulating media $^{5–7}$. In contrast, in the more conducting or semi- conducting complex oxides with perovskite structures, such as doped cuprates and manganites, the relevance of oxygen vacancies is often invoked. Despite a burst- ing body of experimental data that is rapidly becoming available 8–12 the precise mechanism behind the physical effect of RS remains elusive. A few qualitative models have been proposed emphasizing different aspects: elec- tric field-induced defect migration $^{5,13,14}$, phase separa- tion $^{15}$, tunneling across interfacial domains$^{16}$, control of Shottky barrier’s height $^{3,17}$, etc. A general consensus has emerged on the empirical relevance of three key features: (i) a highly spatially inhomogeneous conduction in the low resistive state, (ii) the existence of a significant num- ber of oxygen vacancy defects and (iii) a preeminent role played by the interfaces, namely, the regions of the oxide that are near each of the metallic electrodes which of- ten form Schottky barriers. Here, we shall introduce and The second important feature incorporated into our model is the relevance of defects within the dielectric. Several experiments point to a preeminent role played by oxygen vacancies $^{5,14,18,19}$. Moreover, it is a universal and salient feature of TMO that their resistivity is dramati- cally affected by the precise oxygen stoichiometry. One may thus expect that oxygen vacancy concentration may be the most significant parameter controlling the local re- sistivity, ρ , of a given material. This feature is included in our model by assuming that each nano-domain of the path is characterized by a certain concentration of oxy- gen vacancy defects, δ . We adopt the most simple linear relation ρ ∝ δ , which follows from the fact that in TMO perovskites the presence of oxygen vacancies severely dis- rupts the electronic conduction properties. Nevertheless, we emphasize that the specific form of ρ ( δ ) is not crucial for the results that we shall describe later on. The third important feature that our model incorpo- rates is the key role played by the interfaces $^{16}$, namely, Several experiments revealed that the conduction in the low resistive state is highly inhomogeneous and dom- inated by one dimensional paths that are associated with enhanced conduction channels $^{5,7}$. These paths would be created upon an initial application of strong electric fields, that bring the dielectric close to its breakdown point. Thus, we shall assume that the electric trans- port is dominated by a single conductive path embedded within a more insulating host. study the behavior of a simple model that incorporates, at a qualitative level, those three features. By means of a numerical simulation we shall show that the model correctly reproduces key non trivial hysteresis cycles ob- served in experiments on perovskite-type transition metal oxides (TMO). II. MODEL I. INTRODUCTION arXiv:1001.0703v1 [cond-mat.mtrl-sci] 5 Jan 2010