Chemically-inactive interfaces in thin film Ag/AgI systems for resistive switching memories

Cho, Deok‐Yong; Tappertzhofen, Stefan; Waser, Rainer; Valov, Ilia

doi:10.1038/srep01169

Cited by 24 publications

(17 citation statements)

References 18 publications

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“…Electrochemical memory (ECM), also known as programmable metallization cell (PMC) or conductive bridge RAM, is a semiconductor nanodevice based on the growth/dissolution of a metallic CF within a solid‐state electrolyte, such as GeS 2 , GeSe, Ag 2 S, Cu 2 S, AgI, amorphous Si, oxides and even organic materials . ECM have found application in non‐volatile memory devices, non‐volatile switches in programmable logic, nanowire logic gates and artificial neural networks, where the ECM can emulate the neuron synapse thanks to its voltage‐adjustable conductance .…”

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confidence: 99%

Impact of the Mechanical Stress on Switching Characteristics of Electrochemical Resistive Memory

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with electrode size as small as 5 nm. [ 26 ] Whereas low-power operation [ 3 ] and fast switching [ 15 ] were demonstrated in ECMs, recent experiments on ECM devices [ 25,27 ] have questioned the long-term stability of the CF, which is necessary to enable nonvolatile storage of data. To assess the switching behavior and CF stability in ECMs, the detailed evolution of electrical, chemical and mechanical forces in the CF must be understood. Figure 2 a shows the measured current-voltage ( I -V ) curve for an ECM with Ag top electrode, GeS 2 electrolyte and W bottom electrode during set and reset transition. Details about the preparation of the ECM devices can be found elsewhere. [ 15 ] The set transition from high to low resistance takes place at V set ≈ 0.3 V, while the reset transition to high resistance occurs at V reset . In the set process, the CF is fi rst formed by nucleation [ 28,29 ] followed by CF growth, [ 6,24 ] which is activated by positive ion migration as shown in Figure 2 b: metallic ions from the reactive-metal electrode (Ag) hop among localized states separated by energy barriers E A0 in amorphous GeS 2 . The electric fi eld lowers the ion-migration barrier to the value:where α = 0.3 is a barrier-lowering coeffi cient (see Figure S1 in the Supporting Information for a complete list of all model parameters used in the simulation) and V is the voltage across the electrolyte. [ 6,24,30 ] Barrier lowering enhances the hopping rate in the fi eld direction, thus increasing the growth rate of the CF diameter φ according to:where A is a pre-exponential constant proportional to cation mobility, T is the local temperature at the CF and E A was obtained from Equation 1 . In Equation 2 , E A controls ion migration in the vertical direction from top to bottom electrode, while the accumulation of defects along the CF causes growth in the radial direction, which is captured by the parameter φ (e.g., see Figure 1 c). Note that the parameter φ represents an effective CF diameter, to properly describe non-cylindrical (e.g., conical) CF shapes and the case of multiple fi laments contributing to the resistive switching. [ 12,26 ] For instance, in the case of multiple fi laments the effective diameter in Equation 2 obeys φ 2 = Σ φ i 2 , where φ i represents the diameter of the individual i -th fi lament and φ properly describes the resistance R ∝ φ −2 of the set state.To control the size of the growing CF during the set transition, the current was kept equal to a compliance value I C = 1 mA in Figure 2 a, thus resulting in a resistance of about 0.3 kΩ in the set state. The current-controlled CF growth was Resistive switching in oxides and other insulating materials provides a promising approach to nanoscale memory devices, where the stored logic state can be changed by activating/deactivating a conductive fi lament (CF). [ 1,2 ] Among resistive switching devices, the electrochemical memory (ECM) attracts strong interest because of outstanding properties such as extremely small programming current, [ 3 ] fast switching...

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Impact of the Mechanical Stress on Switching Characteristics of Electrochemical Resistive Memory

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“…Excluding from the discussion all possible mechanical/morphological effects such as hillocks, lattice mismatch etc., there are several interface interactions being often overlooked but of significant importance. We found out that in some systems e.g Ag/AgI, metallic Ag nanoclusters penetrate into the solid electrolyte (30) and in the case of thinner electrode films (up to 20 nm) this intermixing leads to a complete loss of contact. The process is enhanced by applying a voltage through the cell.…”

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confidence: 98%

(Keynote) Atomic Scale and Interface Interactions in Redox-Based Resistive Switching Memories

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Controlling electrochemical processes at interfaces or within thin films at the atomic scale is a key factor for further development of future nanoelectronics and information technology. This aspect becomes even more important considering concepts beyond conventional data storage like neuromorphic and memristive systems, demonstrating learning abilities and allowing logic operations. In redox-based resistive switching memories (ReRAMs), the solid electrolyte thickness varies in the range between few nanometers up to some ten nanometers. Due to the small dimensions, the high electric fields in the order of E ~ 10 8 Vm -1 , and current densities of j ~ 10 9 Acm -2 , the interface regions are dynamically changing as a function of the thermodynamic and operation conditions. The paper presents an overview on the current state-of-the-art knowledge on atomically scaled processes and interactions, focusing on the electrochemical dynamics at the metal/solid-electrolyte interfaces of nanoscaled thin films and quantum effects.

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“…Ag metallic nanoclusters were found to be incorporated into AgI films (Figure 4 a) during the cell preparation process, but also during retention tests, and device operation. [39] This phenomenon leads to a loss of electrode/electrolyte contact and ReRAM failure in cases where the Ag electrode is thinner thañ 80 nm. A strong chemical interaction was reported for the Ag/GeS x system, leading to partial or complete dissolution (Figure 4 b) of the active electrode.…”

Section: Electrode-electrolyte Interface Dynamicsmentioning

confidence: 99%

Redox‐Based Resistive Switching Memories (ReRAMs): Electrochemical Systems at the Atomic Scale

2013

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Resistive switching memories (RRAMs) are an emerging research field, which is currently of focused interest for both the interdisciplinary scientific community and industry. RRAMs are nano‐electrochemical systems with great potential as a disruptive technology for the semiconductor industry as well as for a number of applications such as memory, logic and analog circuits, memristive operations, neuromorphic applications and computing. The present review aims to present the current state‐of‐the‐art knowledge on redox‐based resistive switching RRAMs, highlighting the role of the interfaces, discussing the electrochemical kinetics during formation of nanofilaments, and to relate them to the more fundamental issue of microscopic description of electrochemical processes at the atomic scale.

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Chemically-inactive interfaces in thin film Ag/AgI systems for resistive switching memories

Cited by 24 publications

References 18 publications

Impact of the Mechanical Stress on Switching Characteristics of Electrochemical Resistive Memory

Impact of the Mechanical Stress on Switching Characteristics of Electrochemical Resistive Memory

(Keynote) Atomic Scale and Interface Interactions in Redox-Based Resistive Switching Memories

Redox‐Based Resistive Switching Memories (ReRAMs): Electrochemical Systems at the Atomic Scale

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