Forming and switching mechanisms of a cation-migration-based oxide resistive memory. Nanotechnology 21(42), 425205

International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan.
Nanotechnology (Impact Factor: 3.82). 10/2010; 21(42):425205. DOI: 10.1088/0957-4484/21/42/425205
Source: PubMed


We report detailed current-voltage and current-time measurements to reveal the forming and switching behaviors of Cu/Ta(2)O(5)/Pt nonvolatile resistive memory devices. The devices can be initially SET (from the OFF state to the ON state) when a low positive bias voltage is applied to the Cu electrode. This first SET operation corresponds to the first formation of a metal filament by inhomogeneous nucleation and subsequent growth of Cu on the Pt electrode, based on the migration of Cu ions in the stable Ta(2)O(5) matrix. After the forming, the device exhibits bipolar switching behavior (SET at positive bias and RESET (from the ON state to the OFF state) at negative bias) with increasing the ON resistance from a few hundred Ω to a few kΩ. From the measurements of the temperature stability of the ON states, we concluded that the RESET process consists of the Joule-heating-assisted oxidation of Cu atoms at the thinnest part of the metal filament followed by diffusion and drift of the Cu ions under their own concentration gradient and the applied electric field, disconnecting the metal filament. With ON resistances of the order of a few kΩ, the SET and RESET operations are repeated by the inhomogeneous nucleation and the Joule-heating-assisted dissolution of a small filament on a remaining filament. This switching model is applicable to the operation of cation-migration-based resistive memories using other oxide materials.

Download full-text


Available from: Tohru Tsuruoka, Sep 08, 2014
  • Source
    • "Figures 6(e) and (f) show a cross-section TEM image and an EDX map of an area far from the conducting point, which in turn show the existence of Cu ions along the interface between the bottom Pt electrode and the Ta 2 O 5 layer. The dome-shaped structure supports our understanding of the switching mechanism [12], although the part of the Figure 5. (a) Schematic of the turning-ON of a Cu/Ta 2 O 5 /Pt device with an external resistor, connected in series with the voltage source, acting as a current limiter. (b) Current–voltage sweep to turn-ON the device with the external resistor and a compliance current of 300 nA. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Resistive random access memories (ReRAMs) are promising next-generation memory devices. Observation of the conductive filaments formed in ReRAMs is essential in understanding their operating mechanisms and their expected ultimate performance. Finding the position of the conductive filament is the key process in the preparation of samples for cross-sectional transmission electron microscopy (TEM) imaging. Here, we propose a method for locating the position of conductive filaments hidden under top electrodes. Atomic force microscopy imaging with a conductive tip detects the current flowing through a conductive filament from the bottom electrode, which reaches its maximum at a position that is above the conductive filament. This is achieved by properly biasing a top electrode, a bottom electrode and the conductive tip. This technique was applied to Cu/Ta2O5/Pt atomic switches, revealing the formation of a single Cu filament in a device, although the device had a large area of 5 × 5 μm(2). Change in filament size was clearly observed depending on the compliance current used in the set process. It was also found from the TEM observation that the cross-sectional shape of the formed filament varies considerably, which is attributable to different Cu nuclei growth mechanisms.
    Full-text · Article · Mar 2015 · Nanotechnology
  • Source
    • "It is worth noticing that the voltage behavior of í µí¼ SBD is similar to literature data regarding the same insulator and different electrodes [5], but also different insulator, electrodes, and thickness [31]. Our data were compared with simulations performed with the procedure described above. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a model of the kinetics of reversible breakdown in metal-insulator-metal structures with afnia based on the growth of fractal patterns of defects when the insulator is subject to an external voltage. The probability that a defect is (or is not) generated and the position where it is generated depend on the electric field distribution. The new defect moves accordingly to fractal rules and attach to another defect in a tree branch. When the two electrodes sandwiching the insulating film are connected a conductive filament is formed and the breakdown takes place. The model is calibrated with experiments inducing metastable soft breakdown events in Pt/HfO2/Pt capacitors.
    Full-text · Article · Jan 2015 · Advances in Condensed Matter Physics
  • Source
    • "The LRSAEHRS switching is called the RESET phenomenon. Previous studies showed that the filament cannot be completely dissolved, leaving residual conduction paths [2]. In this case, the cell cannot returns in its pristine resistance state. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This work deals with the study of electrochemical metallization memory cells (ECM) also called CBRAM (Conductive Bridge RAM). Memory stacks were fabricated by sputtering onto SiO2/Si substrates and were characterized by atomic force microscopy and a mercury drop probe. These stacks employ a Ge2Sb2Te5 (GST) layer as a solid electrolyte which has been barely employed in CBRAM devices. Electrical measurements demonstrate resistance switching of the stacks due to the formation/dissolution of metallic filaments within the GST layer. However, the memory elements featuring a silver top electrode do not exhibit such switching behavior but show instead an ohmic behavior. This result is interpreted through physical analysis revealing the presence of silver in each layer of the memory devices. Finally, a physical model is presented. This model was used to interpret adequately the bipolar resistance switching phenomenon observed in the memory stacks.
    Full-text · Conference Paper · Jun 2014
Show more