Rupture Of Conductive Filaments Research Articles

Anisotropic Magnetoresistance of Ferromagnetic Conductive Filament in Resistive Switching Memory

A resistive switching (RS) memory has been expected to be a next-generation memory owing to its high density, low power consumption, and high switching speed. The mechanism of the reversible RS phenomenon has been considered in terms of the formation and rupture of conductive filaments (CF). Recently, it has been reported that a ferromagnetic CF was formed in NiO-based RS memory. This suggested the possibility of the new device that has both RS memory and spintronics device functions. The presence of a ferromagnetic CF in the NiO layer was confirmed by measuring the magnetization of the large number of CFs at room temperature using a SQUID magnetometer. Although, it is not yet confirmed that a single ferromagnetic CF is formed by the SET process. The purpose of this study is to understand the physical properties of a single ferromagnetic CF by focusing on magnetoresistance (MR). We prepared Ni/HfO2/Pt memory device, having ferromagnetic Ni electrode and the oxide of a non-magnetic metal. The fabricated RS memory devices have a cross-bar structure. The crossed electrode size is 1×1 mm2. RS characteristic was measured with the bipolar operation mode. When current limit is 5 mA, the anisotropic magnetoresistance (AMR) was observed in the low resistance state. The direction of the external magnetic field is in-plane to the substrate, and the current is perpendicular to the magnetic field. The AMR showed a convex behavior with magnetic field, and the MR ratio was approximately 0.15%. It is strongly suggested that AMR came from a ferromagnetic CF formed in the oxide layer. Further discussions will be shown in the workshop.

Resistive switching in epitaxial BaTiO3 films grown on Nb-doped SrTiO3 by PLD

Abstract 100-nm-thick epitaxial BaTiO 3 (BTO) films were prepared on the Nb-doped SrTiO 3 (NSTO) single-crystal substrates by pulsed laser deposition. Bipolar resistive switching (RS) behavior was observed in the as-prepared BTO/NSTO samples, which was attributed to the formation and rupture of conductive filaments in the BTO films. The RS effect was suppressed after the samples were annealed in air due to the decrease in oxygen vacancies during annealing, which was confirmed by X-ray photoelectron spectroscopy (XPS) measurements. The current–voltage curves of the as-prepared samples show linear ohmic conduction at the low resistive state and space-charge-limited conduction (SCLC) at the high resistive state, respectively. SCLC dominated in the annealed samples.

Switching mechanism in Au nanodot-embedded Nb2O5 memristors.

Resistive switching behavior of Au nanodot-embedded Nb2O5 memristor devices is reported. Due to controlled formation and/or rupture of conductive filaments; Au nanodot-embedded Nb2O5 devices show better consistency during transition from high to low resistance state and vice-versa. The memristive transition is explained using a physical model which involves oxygen ion, O(2-) trapping or detrapping at the metal-oxide interface, and O(2-) transport and annihilation with the oxygen vacancies in the breakdown percolation path. The experimental results indicate that Au nanodot-embedded Nb2O5 memristors may find applications as non-volatile memory devices.

Origin of the OFF state variability in ReRAM cells

This work exploits the switching dynamics of nanoscale resistive random access memory (ReRAM) cells with particular emphasis on the origin of the observed variability when cells are consecutively cycled/programmed at distinct memory states. It is demonstrated that this variance is a common feature of all ReRAM elements and is ascribed to the formation and rupture of conductive filaments that expand across the active core, independently of the material employed as the active switching core, the causal physical switching mechanism, the switching mode (bipolar/unipolar) or even the unit cells' dimensions. Our hypothesis is supported through both experimental and theoretical studies on TiO2 and In2O3 : SnO2 (ITO) based ReRAM cells programmed at three distinct resistive states. Our prototypes employed TiO2 or ITO active cores over 5 × 5 µm2 and 100 × 100 µm2 cell areas, with all tested devices demonstrating both unipolar and bipolar switching modalities. In the case of TiO2-based cells, the underlying switching mechanism is based on the non-uniform displacement of ionic species that foster the formation of conductive filaments. On the other hand, the resistive switching observed in the ITO-based devices is considered to be due to a phase change mechanism. The selected experimental parameters allowed us to demonstrate that the observed programming variance is a common feature of all ReRAM devices, proving that its origin is dependent upon randomly oriented local disorders within the active core that have a substantial impact on the overall state variance, particularly for high-resistive states.

Physical model of dynamic Joule heating effect for reset process in conductive-bridge random access memory

Dynamic Joule heating effect of reset process in conductive-bridge random access memory (CBRAM) was investigated theoretically. By introducing the geometry effect of conductive filament (CF), the temperature and electric field distributions in the transient state in both one-dimen-sional and three-dimensional cases were discussed in detail. We found that the CF's geometry plays an important role in the transient Joule heating process, and the transient thermal effect turns increasingly significant with increasing applied voltage in reset procedure. The proposed position where CF ruptures is between the location of temperature peak and narrow end of the CF rather than the point of temperature peak in the cone-shaped CF system. It is more interesting that the rupture of CF possibly occurs in transient process, before steady-state is established.

Voltage and power-controlled regimes in the progressive unipolar RESET transition of HfO₂-based RRAM.

Resistive switching (RS) based on the formation and rupture of conductive filament (CF) is promising in novel memory and logic device applications. Understanding the physics of RS and the nature of CF is of utmost importance to control the performance, variability and reliability of resistive switching memory (RRAM). Here, the RESET switching of HfO2-based RRAM was statistically investigated in terms of the CF conductance evolution. The RESET usually combines an abrupt conductance drop with a progressive phase ending with the complete CF rupture. RESET1 and RESET2 events, corresponding to the initial and final phase of RESET, are found to be controlled by the voltage and power in the CF, respectively. A Monte Carlo simulator based on the thermal dissolution model of unipolar RESET reproduces all of the experimental observations. The results contribute to an improved physics-based understanding on the switching mechanisms and provide additional support to the thermal dissolution model.

Investigation of Thomson Effect in Cu/TaOx/Pt Resistive Switching Memory

Conductive bridge random access memory (CBRAM) shows strong potential for replacing flash memory on the sub-20 nm technology nodes. The switching mechanism is primarily attributed to the electrochemical formation and rupture of conductive filaments. In Cu/TaOx/Pt devices, high electric current in the RESET process can cause significant local heating. Thomson heating effect has to be considered due to conical or cylindrical filament geometries giving cause for strong temperature gradients. The thermoelectric effect is evaluated for the Cu and oxygen vacancy nanofilaments in bipolar and unipolar switching modes. The Thomson coefficient for oxygen vacancy filament is extracted from the difference of SET voltages between two switching modes.

Endurance Improvement Technology With Nitrogen Implanted in the Interface of ${\rm WSiO}_{\bf x}$ Resistance Switching Device

Incorporation of nitrogen as an oxygen-confining layer in the resistance switching reaction region is investigated to improve the reliability of resistance random access memory (RRAM). The switching mechanism can be attributed to the formation and rupture of conduction filaments. A compatible WSiON (around 5 nm) layer is introduced at the interface of tungsten silicon oxide (WSiOx) and TiN electrode to prevent the randomly diffusing oxygen ions surpassing the storage region of the WSiON layer. The double-layer WSiOx/WSiON memory structure would enhance the endurance over 100 times so as to better confirm the WSiOx RRAM application of nonvolatile memory.

Resistance switching of thin AlOx and Cu-doped-AlOx films

Thin copper-doped aluminum oxide (Cu-doped-AlOx) and AlOx films of about 5nm thick were generated by oxidizing the surfaces of Al and Al-5wt.% Cu (Al-Cu) films in an oxygen plasma. According to X-ray photoelectron spectroscopy analyses, these two oxide films were found to be deficient in oxygen and had gradient concentrations of Al and O. The oxide films were employed as resistor layers sandwiched between an Al top electrode and an Al or Al-Cu bottom electrode to form resistive memory devices. The devices demonstrated unipolar resistance switching between high resistance state and low resistance state (LRS), and their resistance ratios measured at +0.2V were around 105. Furthermore, their current–voltage characteristics showed ohmic conduction with the resistance increasing with temperature, in LRS. Conductive filaments were thought to form inside the AlOx film and the Cu-doped AlOx film, causing resistive switching. The resistive memory device using the AlOx film had unstable switching behaviors during cyclic testing, whereas the device using the Cu-doped AlOx film demonstrated stable resistance switching during 100cycles of testing. The presence of the Cu ingredient in the AlOx film is likely to facilitate the formation and rupture of conductive filaments and induced stable resistance switching.

On the Resistive Switching and Current Conduction Mechanisms of Amorphous LaGdO3 Films Grown by Pulsed Laser Deposition

The unipolar resistive switching properties of the amorphous LaGdO3 thin films deposited by pulsed laser deposition have been investigated. Reliable and repeatable nonvolatile switching of the resistance of LaGdO3 films was obtained between two well defined states of low and high resistance with nearly constant resistance ratio ~ 106 and non-overlapping switching voltages in the range of 0.6-0.75 V and 2.5-4 V respectively. The current conduction mechanism of the device in low and high resistance states were found to be dominated by the Ohmic behavior and Poole-Frenkel emission respectively. The resistance of low and high resistance states of the film showed no obvious degradation for up to ~ 12 hours indicating good retention. The switching between low and high resistance states was attributed to formation and rupture of conductive filaments. The achieved characteristics of the resistive switching in LaGdO3 thin films seem to be promising for futuristic nonvolatile memory applications.

Physical electro-thermal model of resistive switching in bi-layered resistance-change memory.

Tantalum-oxide-based bi-layered resistance-change memories (RRAMs) have recently improved greatly with regard to their memory performances. The formation and rupture of conductive filaments is generally known to be the mechanism that underlies resistive switching. The nature of the filament has been studied intensively and several phenomenological models have consistently predicted the resistance-change behavior. However, a physics-based model that describes a complete bi-layered RRAM structure has not yet been demonstrated. Here, a complete electro-thermal resistive switching model based on the finite element method is proposed. The migration of oxygen vacancies is simulated by the local temperature and electric field derived from carrier continuity and heat equations fully coupled in a 3-D geometry, which considers a complete bi-layered structure that includes the top and bottom electrodes. The proposed model accurately accounts for the set/reset characteristics, which provides an in-depth understanding of the nature of resistive switching.

Effect of concurrent joule heat and charge trapping on RESET for NbAlO fabricated by atomic layer deposition

The RESET process of NbAlO-based resistive switching memory devices fabricated by atomic layer deposition is investigated at low temperatures from 80 to 200 K. We observed that the conduction mechanism of high resistance state changed from hopping conduction to Frenkel-Poole conduction with elevated temperature. It is found that the conductive filament rupture in RRAM RESET process can be attributed not only to the Joule heat generated by internal current flow through a filament but also to the charge trap/detrapping effect. The RESET current decreases upon heating. Meanwhile, the energy consumption also decreases exponentially. This phenomenon indicates the temperature-related charge trap/detrapping process which contributes to the RESET besides direct Joule heat.

New Resistive Switching Phenomena in Devices with Limited Active Metal Source

ABSTRACTTo better understand the mechanisms of creation and rupture of conductive filaments in resistive switching devices such as Cu/TaOx/Pt, with Cu and Pt being the active and inert electrodes, respectively, a device with limited supply of active metal electrode has been manufactured and electrically characterized. The limited supply of active metal has been realized by depositing a thin (delta) Cu layer (δ-Cu), 6 nm and 12 nm thick, on TaOx, resulting in a Pt/δ-Cu/TaOx/Pt device structure. The limited active metal supply i) has a direct impact on the onresistance (Ron) of the Cu bridge, and leads, after several conventional set-reset cycles, to ii) pulsating behavior, when device turns on and off repeatedly, to iii) symmetric switching behavior with respect to applied voltage polarity, when the device can be set and reset both at positive and negative bias, and to iv) volatile switching behavior.

Nonvolatile Resistive Memory Switching in Amorphous LaGdO3 Thin Films

ABSTRACTNonvolatile unipolar resistive switching properties of the amorphous LaGdO3 thin films deposited by pulsed laser deposition have been studied. Reliable and repeatable switching of the resistance of LaGdO3 film was obtained between low and high resistance states with nearly constant resistance ratio ∼ 106 and non-overlapping switching voltages in the range of ∼0.6-0.75 V and 2.5-4 V respectively. The switching between low and high resistance states was attributed to the formation and rupture of conductive filaments using temperature dependent resistance measurements. The current conduction mechanisms of the LaGdO3 film in low and high resistance states were found to follow the Ohmic behavior and Poole-Frenkel emission respectively. The resistance of low and high resistance states of the film remained nearly constant for up to ∼ 104 seconds indicating good retention. The observed resistive switching characteristics of LaGdO3 thin films are promising for futuristic nonvolatile memories.

Evaluation of the local temperature of conductive filaments in resistive switching materials

The resistive switching effect in metal oxides and other dielectric materials is among the leading future non-volatile memory technologies. Resistive switching is widely ascribed to the formation and rupture of conductive filaments in the oxide, which are generated by temperature-enhanced nano-scale ion migration or other thermal effects. In spite of the central role of the local filament temperature on the switching effect, as well as on the conduction and reliability physics, no measurement methods of the filament temperature are yet available. In this work, we report on a method for evaluating the conducting filament temperature, using a metal–insulator–semiconductor bipolar transistor structure. The filament temperature is obtained by analyzing the thermal excitation rate of electrons from the filament Fermi level into the conduction band of a p-type semiconductor electrode. Measurements were carried out to obtain the conductive filament temperature in hafnia at varying ambient temperatures in the range of 3–300 K. Significant Joule heating of the filament was observed across the entire measured ambient temperature range. The extracted temperatures provide physical insight into the resistive switching effect.

Research of Bilayer Stacked Resistance Switching Memory Structure Based on Pt/NiO/TiO2/Pt

The large power consumption and the wide distribution of switching parameters for unipolar resistance switching are major hurdles to non-volatile memory application. In this letter, the stacked structure Pt/NiO/TiO2/Pt was investigated to overcome the mentioned problems. TiO2 thin film was formed on NiO by oxidation of metallic Ti thin film through rapid thermal process (RTP) in oxygen atmosphere. The sharp TiO2 (202) peak and NiO (200) peak observed by the X-ray diffraction measurement. This stacked bilayer structure is favorable for reducing reset current in comparison with single layer structure. This is attributed to a small amount of heat loss during rupturing process of conductive filaments. It is suggested that the conductive filament rupture and rejuvenation was happened at the interface between TiO2 and NiO by controlling switching sequence. Furthermore, the diffused Ti in NiO also can result in stabilization of switching parameters.

Electrical properties and carrier transport mechanisms of nonvolatile memory devices based on randomly oriented ZnO nanowire networks

AbstractWe report reproducible bipolar resistive memory devices based on Au/ZnO nanowire networks (ZnO NWNs)/ITO, which show a high Ron/Roff ratio (∼104) and narrow dispersion of set and reset threshold voltages. The dominant conduction mechanisms of low resistance state and high resistance state were verified by Ohmic behavior and space charge limited current, respectively. The switching mechanism is confirmed in terms of the formation and rupture of conductive filaments, with oxygen vacancies localized on the ZnO NWNs surface involved in. The Au/ZnO NWNs/ITO devices presented in our work show potential applications in the next generation nonvolatile memory field. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reproducible resistive‐switching behavior in copper‐nitride thin film prepared by plasma‐immersion ion implantation

AbstractCopper nitride film prepared by plasma‐immersion ion implantation (PIII) is demonstrated to exhibit reversible resistance variance character. By forming a gradually distributed nitrogen concentration in the Cu‐nitride film, the nitride‐based memory devices show bipolar nature with a low operation voltage, forming‐free characteristics and a distinguishable resistance ratio. The bipolar switching behavior is attributed to the formation and rupture of conductive filaments within a cycle, which is confirmed by spreading‐resistance images of a conducting atomic force microscope. Based on X‐ray photoelectron spectroscopy (XPS) analysis, semiconducting Cu3N phase and metallic Cu4N phase coexist in the copper nitride film and local conducting filaments might be formed by interconnection of the metallic phases by migration of Cu+ ions under a bias voltage.

Low-Power and Highly Uniform Switching in $ \hbox{ZrO}_{2}$-Based ReRAM With a Cu Nanocrystal Insertion Layer

In this letter, the insertion of a Cu nanocrystal (NC) layer between the Pt electrode and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{ZrO}_{2}$</tex></formula> film is proposed as an effective method to improve resistive switching properties in the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{ZrO}_{2}$</tex></formula> -based resistive switching memory. This Cu/ <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{ZrO}_{2}$</tex></formula> :Cu/Cu NC/Pt memory exhibits asymmetric nonpolar resistive switching behavior, low operating voltage ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 1.2 V), low Reset current <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(&lt; \hbox{50}\ \mu\hbox{A})$</tex></formula> , and high uniformity of resistance switching. The switching mechanism is believed to be related with the formation and rupture of conductive filament. The NC-induced electrical field enhancement has the benefit to accelerate and control the CF formation process, thus leading to low-switching threshold voltage and high uniformity.

Effect of Al doping on resistive switching behavior of NiOx films for nonvolatile memory application

In this work, the authors investigated the effect of Al doping on the resistance switching characteristics of sputtered NiOx films. Pt/NiOx/Pt metal-insulator-metal (MIM) stacks were fabricated by reactive dc magnetron sputtering with various Al contents in NiOx films and the resistance switching behavior of the MIM stack was characterized in conjunction with physical property, such as chemical bonding of NiOx. Al doping into NiOx films improved the endurance of SET/RESET operations, the distribution of VSET, and the memory window compared to the undoped NiOx films. X-ray photoemission spectroscopy showed that the Al doping caused the density of metallic nickel (Ni0) to be increased with the reduction of Ni3+ concentration. It was considered that the increase of metallic nickel (Ni0) in Al-doped NiOx films enhanced the repeated formation and rupture of conductive filaments during resistive switching operation, resulting in the enhanced endurance and the narrowed VSET distribution.