Active Electrode Redox Reactions and Device Behavior in ECM Type Resistive Switching Memories

Abstract

atoms of the active metal, electrically connecting both electrodes through the solid electrolyte. [11] The formation of this filament is preceded by (partial) oxidation of the active electrode under positive bias. Because of field accelerated transport, the so-formed cations are migrating through the solid electrolyte thin film (e.g., Ta 2 O 5 , HfO 2 , or SiO 2 ) toward the counter electrode. The cations are reduced at the negatively charged counter electrode and form a nucleus facilitating further fast filament growth. Filament growth continues until short circuit conditions are reached and the driving forces for the electrochemical redox processes and ion migration are diminished. The transition from the high resistive state (HRS) into a low resistive state (LRS) is the SET process. When a negative bias is applied to the active electrode, the filament is disrupted and driven by same forces, but in opposite direction it is assumed to be completely dissolved. The device is switched from LRS to HRS that is the RESET.Since electrochemical electrode processes are spatially separated, SET event requires a counter electrode reaction at the CE to keep overall electroneutrality of the system. For most oxide-based solid electrolytes, this counter reaction involves a reduction of moisture, incorporated in the films from the ambient or during preparation steps (e.g., lithography, rinsing, atomic layer deposition (ALD) deposition, etc.). Reduction of water is kinetically favorable compared to reduction (and decomposition) of the oxide itself [12] and therefore the redox processes related to moisture can be a limiting factor for the switching kinetics. [13] Furthermore, incorporated moisture can also enhance the cation mobility. [14] In ECM devices, typically silver or copper electrodes are used. In addition, metals such as Ti [15] or alloys/compounds have been suggested as active electrodes. [16,17] The advantage of these alternative systems is considered to be the direct supply of mobile ions, avoiding the necessity of direct electrode oxidation and related energy consumption. However, in most of the cases the choice of active electrode materials is based mainly on empirical observations and the electrochemical properties of the materials toward oxidation and reduction have not been considered.In this work, we investigate the electrochemical redox behavior of several metals covering a range from noble to transition metals (Ag, Al, Au, Cu, Fe, Ni, Ta Ti, V, and Zr) as active electrode materials using Me/SiO 2 /Pt system. Cyclic voltammetry (CV) measurements are used to provide information on the redox processes occurring prior to the switching events. In addition, we performed I-V switching experiments with three different thicknesses of the solid electrolyte down to 5 nm Electrochemical metallization cells rely on oxidation, reduction, and migration of metal cations in nanoscale thin films. The cations are typically provided by the oxidation of the active electrode. Commonly, Cu, Ag, or their compounds are used as electro...

Parylene Based Memristive Devices with Multilevel Resistive Switching for Neuromorphic Applications

“…Thus, the lifetime of Cu bridges is longer and, hence, the plasticity of Cu samples is better. This result is also confirmed by a recent study by Valov et al [46], where the filament stability and retention properties of ECM devices were found to be determined by the Gibbs free energy of formation of cations.…”

“…Note that although the question of the nature of RS in M/PPX/ITO structures is extremely interesting, its detailed analysis lies beyond the scope of this study. Here, based on the experimental data and on the related literature, we only make the following conclusion: the bipolar RS behavior of the investigated samples most likely originates from the formation/destruction of metal bridges (filaments) in the dielectric parylene layer due to migration of metal cations (Ag + , Cu + /Cu +2 , Al +3 or Ti +4 ) from the top electrode toward the bottom during the SET process under strong electric field [1,3,30,35,46]. In contrast, according to the molecular dynamics simulations performed by Ielmini et al [30], the conductive bridges can spontaneously break during the RESET switching as a result of atomic surface diffusion driven by the minimization of the system energy.…”

Van der Waals Epitaxy of Horizontally Orientated Bismuth Iodide/Silicon Heterostructure for Nonvolatile Resistive‐Switching Memory with Multistate Data Storage

“…experimentally demonstrated that Au can intrude into the insulator to form a conductive filament based on electrochemical metallization mechanism, which results in a resistive switching behavior in a Pt/SiO 2 /Au device. [ 72 ] Meanwhile, an electric field of at least 1.4 MV cm −1 is required to initiate oxidation of the energetically unfavorable Au. This magnitude is significantly higher than that required to activate the OTS device.…”

A Low‐Current and Analog Memristor with Ru as Mobile Species

“…Such devices, even though very useful for many applications, still need improvement for many other applications that need a retention for over a year at room temperature (RT) or above. It has been verified recently that even inert metals, such as Pd, Pt, or Au, could play the role of mobile cations in oxide layer, [34,46,47] inducing an ECM-like switching behavior. In addition, it has been demonstrated that metal cations (e.g., Ta, Hf, and Ti) can be mobile under certain conditions in traditional VCMs with binary oxides.…”