Forming and switching mechanisms of a cation-migration-based oxide resistive memory.
ABSTRACT 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.
Advances in Condensed Matter Physics 01/2015; 2015:1-8. DOI:10.1155/2015/136938 · 1.01 Impact Factor
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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.Nanotechnology 03/2015; 26(14):145702. DOI:10.1088/0957-4484/26/14/145702 · 3.67 Impact Factor
Conference Paper: Synaptic plasticity and memristive behavior operated by atomic switches[Show abstract] [Hide abstract]
ABSTRACT: We demonstrate that the resistive switching memory, called an atomic switch, emulates the synaptic plasticity underlying short-term and long-term memory formations in the human brain. The change in conductance of the atomic switch is considered analogous to the change in strength of a biological synapse that varies according to stimulating input pulses. The atomic switch also exhibits conventional memristive behavior in which the output depends on the history of input signal. These observations indicate that the atomic switch has potential for use as an essential building block for neural computing systems.2014 14th International Workshop on Cellular Nanoscale Networks and their Applications (CNNA); 07/2014