Resistive Switching and Redox Process at the BaTiO₃/(La,Sr)MnO₃ Multiferroic‐Type Interface

Abstract

Resistive switching in oxide‐based structures is intensively studied for the development of ultra‐fast non‐volatile memories with low consumption and neuromorphic electronic devices. Here, evidence of interface‐controlled, reversible, bi‐polar resistance switch in prototype multiferroic BaTiO3/La0.75Sr0.25MnO3 (BTO/LSMO) system is given. The analysis of current–voltage hysteresis curves of a thick Au/BTO/LSMO structure reveals the existence of a 2.55 nm‐thick barrier layer at the bottom BTO/LSMO interface, leading to a tunnel electroresistance of ≈1700%. In the native state where BTO polarization points downward, high resolution electron microscopy and electron energy loss spectroscopy show Ba/(La,Sr) and Ti/Mn cationic intermixing, together with a valency reduction of Mn cations and an oxygen deficiency at the interface. This results in a high resistance state, due to partial loss of the metallicity and of the double exchange magnetic interaction in the oxygen‐deficient LSMO. The switch to the low resistance state, achieved by upward electric field, is explained in terms of re‐oxydation of Mn cations at the interface (decrease of the Mn3+/Mn4+ ratio), with oxygen vacancies migration from LSMO to BTO. This work emphasizes the crucial role of ionic exchanges and of redox processes at interfaces, both on ferroelectric bound charge screening and on resistive switching.

Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space‐Charge Phenomenon

“…The reasons for fast oxygen diffusion along extended defects in LSMO are not clear, [21][22][23] however; such knowledge is essential for tuning oxide-ion transport in LSMO for application as a cathode material in solid oxide fuel cells (SOFC) [24][25][26][27] or as the active material in memristive devices. [28][29][30][31][32][33][34] In ionic solids, there are two possibilities to explain the pheno menon of fast diffusion along dislocations [23] (see Figure 1a): (i) diffusion along the dislocation core is faster than in the bulk on account of the activation barrier for ion migration being lower in the core than in the bulk, as is the case in metals; (ii) the concentration of the defects responsible for diffusion is strongly enhanced in a space-charge tube surrounding the dislocation. [23,35,36] For LSMO, literature provides at present an unclear picture.…”

Wireless Multiferroic Memristor with Coupled Giant Impedance and Artificial Synapse Application

“…Meanwhile the integration of storage, processing, and wireless communication of information with a single device has not been reported for previous ferroelectric and multiferroic materials, which is important for the application of memristor in the IoT nodes. We also notice that the recently proposed Ag/PZT/Nb:SrTiO 3 FTJ, [ 31 ] Ni/PZT/Nb‐doped SrTiO 3 heterojunction [ 32 ] and Au/BaTiO 3 /La 0.75 Sr 0.25 MnO 3 multiferroic structure [ 39 ] could provide obviously higher on‐off ratios than that of proposed multiferroic memristor, since the FTJ usually utilizes the tunneling effect of ultrathin ferroelectric film, while the thickness of ferroelectric layer in this study is several orders of magnitude larger. By decreasing the thickness of PZTM layer and integrating the FTJ with proposed multiferroic heterostructure, the on‐off ratio can be improved significantly.…”

“…The other one is to utilize the multilevel polarization switching of ultrathin piezoelectric film. [30,31] Additionally other multiferroic memristors based on FTJ [32] and resistive switching [39] have been also investigated recently.…”

Second‐Order Memristor Based on All‐Oxide Multiferroic Tunnel Junction for Biorealistic Emulation of Synapses

“…It has been shown [32,33,38] that the mixing of ions at the BTO/ LSMO interface significantly modifies the properties of the interfacial layers of the LSMO film. The Mn 3+ /Mn 4+ ratio can deviate from the optimal point, which leads to the breakdown of the double exchange mechanism along the chains; this, in turn, induces a metal-insulator transition (MIT) in the LSMO interfacial layers.…”

“…An equivalent effect has been demonstrated via the insertion of a thin layer of La 1‐x Ca x MnO 3 between BTO and LSMO. [ 39 ] Remarkably, the MIT effect at LSMO interfaces can be made controllable: voltage application can either induce migration of oxygen vacancies, which will change the redox nature of the chains, [ 38 ] or induce BTO FE switching, which will likewise change the electrostatic charges at the interfaces. [ 40,41 ] The LSMO/BTO/LSMO system thus provides the interplay ground between BTO FE ordering and charge ordering from Mn cations.…”