Nanoscale cation motion in TaOx, HfOx and TiOx memristive systems

Wedig, Anja; Luebben, Michael; Cho, Deok‐Yong; Moors, Marco; Skaja, Katharina; Rana, Vikas; Hasegawa, Tsuyoshi; Adepalli, Kiran Kumar; Yildiz, Bilge; Waser, Rainer; Valov, Ilia

doi:10.1038/nnano.2015.221

Cited by 548 publications

(470 citation statements)

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“…At the Pt/MeO x interface OH − can be incorporated (within nanopores) in accordance to Equation (5) or OH O • can be formed (according to Equation (1)). In the latter case this charge will also require compensation and will lead to reduction of the solid electrolyte.…”

Section: Resultsmentioning

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.…”

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confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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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“…[1][2][3][4][5] There has been particular interest in understanding the role of migration of oxygen atoms in determining the operation of memristors. 6-11 Similar recent advances in understanding the localized nanoscale physico-chemical changes underlying resistance switching 4,12-15 have opened up fresh interests into studying the effect of atomic movements on extended device operation and the nanoscale material behavior during eventual failure and possible techniques to mitigate such failure.…”

Section: Introductionmentioning

confidence: 99%

Oxygen migration during resistance switching and failure of hafnium oxide memristors

Kumar

Wang

Huang

et al. 2017

Applied Physics Letters

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Metal-oxide memristors, or resistive random access memory (RRAM) switches, in particular utilizing HfO x as the resistive switching material, have seen significant interest recently for nonvolatile memory and computation applications. [1][2][3][4][5] There has been particular interest in understanding the role of migration of oxygen atoms in determining the operation of memristors. 6-11 Similar recent advances in understanding the localized nanoscale physico-chemical changes underlying resistance switching 4,12-15 have opened up fresh interests into studying the effect of atomic movements on extended device operation and the nanoscale material behavior during eventual failure and possible techniques to mitigate such failure. [16][17][18] To enable scanning transmission x-ray microscopy (STXM) measurements, each device was built on a 200 nm low-stress Si 3 N 4 film suspended over 50 µm x 50 µm holes etched through a silicon substrate. 13 We fabricated crosspoint HfO x devices with an active area of 2 µm x 2 µm ( Figure 1a) by depositing a bottom electrode (15 nm Pt), a blanket layer of 6 nm HfO 2 , followed by the top electrode (10 nm TiN and 15 nm Pt). Typical currentvoltage plots of these devices (Figure 1b) exhibited the well-recognized resistance switching behavior, or pinched hysteresis loop, that characterizes a memristor. 19 During operation, high and low non-volatile resistance states (also called OFF and ON, respectively) were repeatedly accessed using bipolar voltage pulses. STXM experiments were performed using resonantly tuned x-ray beams mostly in the O K-edge region, with spectral resolution of ~70 meV and a beam diameter <30 nm. 20 The device was electrically connected inside the chamber of the system to enable in-situ operation and ON/OFF cycling to emulate ageing of the memristor. The x-ray absorption spectrum of the material stack within a device crosspoint before its operation (Figure 2a) revealed oxygen bonds to both Hf and Ti, suggesting oxidation of Ti upon sputter deposition of TiN onto HfO 2 and a resulting mixture of Ti and Hf oxides. We used the absorption of the pre O K-edge at 522 eV to monitor total thickness and other structural modulations (especially electrode distortions), the intensity of the 531 eV peak (the lowest conduction band of the stack) as an indicator of the relative conductivity within the crosspoint, 1,21 and the post O K-edge at 570 eV to determine the local oxygen concentration in the film.

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“…In addition, ambient effects on resistive switching suggest that the defects responsible for switching are hydrogen-passivated or are in some way protected from direct reaction with ambient oxygen and water until a switching events occurs [56,63]. The detailed interactions between ambient gases and proton (or cation) mobility is an important topic that may provide a deeper understanding of resistive switching mechanisms [64][65][66][67][68], specifically those in oxide-based valence change memory (VCM)-type ReRAMs [69][70][71]. The models used here to describe the possible SiO x -based RS mechanisms differ from most conventional models by considering that the defects responsible for RS may remain localized within the switching region so that resistive switching occurs when a collection of defects are driven between conductive and nonconductive forms [56].…”

Section: Resultsmentioning

confidence: 99%

Review of Recently Progress on Neural Electronics and Memcomputing Applications in Intrinsic SiOx-Based Resistive Switching Memory

Hsieh¹,

Chang²,

Chen³

et al. 2018

Memristor and Memristive Neural Networks

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In this chapter, we focus on the recent process on memcomputing (memristor + computing) in intrinsic SiO x -based resistive switching memory (ReRAM or called memristor). In the first section of the chapter, we investigate neuromorphic computing by mimicking the synaptic behaviors in integrating one-diode and one-resistive switching element (1D-1R) architecture. The power consumption can be minimized further in synaptic functions because sneak-path current has been suppressed and the capability for spike-induced synaptic behaviors has been demonstrated, representing critical milestones and achievements for the application of conventional SiO x -based materials in future advanced neuromorphic computing. In the next section of chapter, we will discuss an implementation technique of implication operations for logic-in-memory computation by using a SiO x -based memristor. The implication function and its truth table have been implemented with the unipolar or nonpolar operation scheme. Furthermore, a circuit with 1D-1R architecture with a 4 × 4 crossbar array has been demonstrated, which realizes the functionality of a one-bit full adder as same as CMOS logic circuits with lower design area requirement. This chapter suggests that a simple, robust approach to realize memcomputing chips is quite compatible with large-scale CMOS manufacturing technology by using an intrinsic SiO x -based memristor.

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Nanoscale cation motion in TaOx, HfOx and TiOx memristive systems

Cited by 548 publications

References 36 publications

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

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

Oxygen migration during resistance switching and failure of hafnium oxide memristors

Review of Recently Progress on Neural Electronics and Memcomputing Applications in Intrinsic SiOx-Based Resistive Switching Memory

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Nanoscale cation motion in TaOx, HfOx and TiOx memristive systems

Cited by 548 publications

References 36 publications

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

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

Oxygen migration during resistance switching and failure of hafnium oxide memristors

Review of Recently Progress on Neural Electronics and Memcomputing Applications in Intrinsic SiOx-Based Resistive Switching Memory

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Product

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

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