Graphene‐Modified Interface Controls Transition from VCM to ECM Switching Modes in Ta/TaO<i><sub>x</sub></i> Based Memristive Devices

Lübben, Michael; Karakolis, Panagiotis; Ioannou‐Sougleridis, V.; Normand, P.; Dimitrakis, P.; Valov, Ilia

doi:10.1002/adma.201502574

Cited by 142 publications

(168 citation statements)

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“…Thus, we confirm our recent observations, showing a typical ECM type of switching in TaO x -based devices, explained by Ta ion motion and redox reaction. 23,29 Moreover, formation of Ta filaments, 30 precipitation of Ta metal within TaO x upon cycling, 31,32 and first-principles calculations confirm metallic Ta is formed and is stable within the TaO x matrix, leading to metallic conducting filaments.…”

Section: Resultsmentioning

confidence: 99%

“…Exposing the UHV-annealed TaO x film to the atmosphere leads to instant oxidation of the TaO x surface ( Figure S3) and also absorption of moisture, 29 and this, we believe, is the main reason for the change of the switching mechanism. The samples exposed to the atmosphere showed LRS after SET with anodic tip potential, i.e., reactions c and d at the surface and reactions a and b at the interface.…”

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confidence: 99%

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Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Moors

Adepalli²,

Lu³

et al. 2016

ACS Nano

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108

101

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The local electronic properties of tantalum oxide (TaO x , 2 ≤ x ≤ 2.5) and strontium ruthenate (SrRuO 3 ) thin-film surfaces were studied under the influence of electric fields induced by a scanning tunneling microscope (STM) tip. The switching between different redox states in both oxides is achieved without the need for physical electrical contact by controlling the magnitude and polarity of the applied voltage between the STM tip and the sample surface. We demonstrate for TaO x films that two switching mechanisms operate. Reduced tantalum oxide shows resistive switching due to the formation of metallic Ta, but partial oxidation of the samples changes the switching mechanism to one mediated mainly by oxygen vacancies. For SrRuO 3 , we found that the switching mechanism depends on the polarity of the applied voltage and involves formation, annihilation, and migration of oxygen vacancies. Although TaO x and SrRuO 3 differ significantly in their electronic and structural properties, the resistive switching mechanisms could be elaborated based on STM measurements, proving the general capability of this method for studying resistive switching phenomena in different classes of transition metal oxides. KEYWORDS: resistive switching, strontium ruthenate, tantalum oxide, scanning tunneling microscopy, electric field effect R edox-based resistance switching random access memories (ReRAMs) are considered as the next-generation memory devices to replace the present flash-based technology.1,2 ReRAMs have a simple metal−solid electrolyte− metal architecture, storing binary code information using the change in the resistance induced by filament formation and rupture, defining the low-resistive ON state (also denoted as LRS) and the high-resistive OFF state (or HRS), respectively. High scalability, CMOS compatibility, switching times in the subnanosecond range, excellent endurance and retention, and low power consumption are key but otherwise difficult-toduplicate features of ReRAM devices.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Moors

Adepalli²,

Lu³

et al. 2016

ACS Nano

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108

101

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“…[8] Effects of moisture were already reported for ECM cells based on oxides, e.g., Ta 2 O 5 [8][9][10] and SiO 2 . [11][12][13] It has also been shown that it affects the electrical characteristics in SrTiO 3−x [14] and Ta 2 O 5 [6] -based VCM devices as well. However, the detailed mechanism of this influence in relation to the resistive switching has not been discussed and the question on the influence of oxygen gas, also naturally present in the environment is still open.…”

Section: Introductionmentioning

confidence: 99%

“…However, new studies have demonstrated that the cations in such oxides are often mobile and can participate in the switching process as well. [5,6] Applying a voltage of opposite polarity, the formed filament is partially reoxidized within a thin region facing the high work function metal electrode, defining the OFF state. By modulation of the Schottky barrier at this interface reversible switching between the LRS and HRS is possible.…”

mentioning

confidence: 99%

“…One of the most recent achievements was the experimental verification that redox processes are preceding and directly responsible for the forming itself. [6] Foreign components such as dopants and impurities in molecular or ionic form may significantly influence forming/switching processes in redox-based memories. This work presents a systematic study and discussion on effects of oxygen and moisture in Ta 2 O 5 and HfO 2 thin films, being two of the most used materials for redox-based resistively switching random access memories.…”

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Processes and Effects of Oxygen and Moisture in Resistively Switching TaO_x and HfO_x

Lübben

Wiefels

Waser

et al. 2017

Adv Elect Materials

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but also for being building units for neuromorphic applications and non-von Neumann computing. [1,2] ReRAMs consist of a simple metal-solid electrolyte-metal stack where the information is stored as electronic resistance state of the electrochemical cell. [3] By applying a voltage of different polarity and/or magnitude, formation or rupture of a conductive filament is induced, leading to a nonvolatile low-resistive ON state (also denoted as LRS) or high-resistive OFF state (HRS), respectively. ReRAMs have the advantages of showing low power consumption, fast switching times (down to hundreds of picoseconds), and high endurance and retention. Depending on the working principle, ReRAMs are classified into valence change memory (VCM), electrochemical metallization memory (ECM), or thermochemical memory (TCM). While TCM devices are not of current interest for applications, ECM and VCM show particular promises. The functionality of both types relies on redox reactions and movement of ions and electrons within the solid electrolyte. [3,4] In the case of ECM, the active electrode is (partially) oxidized and metal cations drift within the electrolyte toward the counter electrode where they are reduced back to metal. Due to the high electric fields and high current densities the reduced metallic phase is formed as a tiny (few nm in diameter) filament. [2] The mechanism of VCM devices is considered to be based on a localized partial reduction of the solid electrolyte leading to an oxygen deficient, electrically conductive, filament. Originally the reduction was explained solely by loss of oxygen ions, i.e., formation of additional oxygen vacancies V O •• with a charge, compensated by electrons. However, new studies have demonstrated that the cations in such oxides are often mobile and can participate in the switching process as well. [5,6] Applying a voltage of opposite polarity, the formed filament is partially reoxidized within a thin region facing the high work function metal electrode, defining the OFF state. By modulation of the Schottky barrier at this interface reversible switching between the LRS and HRS is possible. [7] The mechanistic details on the electroforming and switching are still under discussion and despite many studies were performed on this topic, no consensus is reached till today. One of the most recent achievements was the experimental verification that redox processes are preceding and directly responsible for the forming itself. [6] Foreign components such as dopants and impurities in molecular or ionic form may significantly influence forming/switching processes in redox-based memories. This work presents a systematic study and discussion on effects of oxygen and moisture in Ta 2 O 5 and HfO 2 thin films, being two of the most used materials for redox-based resistively switching random access memories. Whereas oxygen is found to not affect the device behavior, the presence of moisture profoundly influences it. It plays a crucial role for the counter electrode reaction, providing additional charg...

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Coexistence of Grain‐Boundaries‐Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride

Pan

Xiao

et al. 2017

Adv Funct Materials

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280

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The use of two dimensional (2D) materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academy and industry. While the research on 2D metallic and semiconducting materials is well established, the knowledge and 2 applications of 2D insulators are still very scarce. In this report we study the presence of resistive switching (RS) in multilayer hexagonal boron nitride (h-BN) using different electrode materials, and we engineer a family of h-BN based resistive random access memories with tunable capabilities.The devices show the coexistence of forming-free bipolar and threshold type RS with low operation voltages down to 0.4 V, high current on/off ratios up to 10 6 , long retention times above 10 hours, as well as low variability. The RS is driven by the grain boundaries (GBs) in the polycrystalline h-BN stack, which allow the penetration of metallic ions from adjacent electrodes. This reaction can be boosted by the generation of B vacancies, which is more abundant at the GBs. To the best of our knowledge, h-BN is the first 2D material showing the coexistance of bipolar and threshold RS, which may open the door to additional functionalities and applications.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

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Graphene‐Modified Interface Controls Transition from VCM to ECM Switching Modes in Ta/TaO_x Based Memristive Devices

Cited by 142 publications

References 36 publications

Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Processes and Effects of Oxygen and Moisture in Resistively Switching TaO_x and HfO_x

Coexistence of Grain‐Boundaries‐Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride

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Graphene‐Modified Interface Controls Transition from VCM to ECM Switching Modes in Ta/TaOx Based Memristive Devices

Cited by 142 publications

References 36 publications

Resistive Switching Mechanisms on TaOx and SrRuO3 Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Resistive Switching Mechanisms on TaOx and SrRuO3 Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Processes and Effects of Oxygen and Moisture in Resistively Switching TaOx and HfOx

Coexistence of Grain‐Boundaries‐Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride

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Graphene‐Modified Interface Controls Transition from VCM to ECM Switching Modes in Ta/TaO_x Based Memristive Devices

Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Resistive Switching Mechanisms on TaO_x and SrRuO₃ Thin-Film Surfaces Probed by Scanning Tunneling Microscopy

Processes and Effects of Oxygen and Moisture in Resistively Switching TaO_x and HfO_x