Modeling of conducting bridge evolution in bipolar vanadium oxide-based resistive switching memory

We investigate the resistive switching characteristics of a Cu/VOx/W structure. The VOx film is deposited by radio- frequency magnetron sputtering on the Cu electrode as a dielectric layer. The prepared VOx sample structure shows reproducible bipolar resistive switching characteristics with ultra-low switching voltage and good cycling endurance. A modified physical model is proposed to elucidate the typical switching behavior of the vanadium oxide-based resistive switching memory with a sudden resistance transition, and the self-saturation of reset current as a function of compliance current is observed in the test, which is attributed to the conducting mechanism is discussed in detail. growth pattern of the conducting filaments. Additionally, the related

Coexistence of unipolar and bipolar modes in Ag/ZnO/Pt resistive switching memory with oxygen-vacancy and metal-Ag filaments

In this study, the unipolar resistive switching （URS） and bipolar resistive switching （BRS） are demonstrated to be coexistent in the Ag/ZnO/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies （Vo） and metal-Ag conducting filaments （CFs） respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching （RS） characteristics （e.g., forming and switching voltages, reset current and resistance states） between these two modes based on Vo- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.

First-principles study of the formation and electronic structure of a conductive filament in ZnO-based resistive random access memory

Oxygen vacancy plays a crucial role in resistive switching. To date, a quantitative study about the distribution of the oxygen vacancies and its effect on the resistive switching has not yet been reported. In this study, we report our first-principles calculations in Zn O-based resistive switching memory grown on a Pt substrate. We show that the oxygen vacancies prefer to be located in the Zn O（0001） plane, i.e. in the direction parallel to the film surface in the preparation process. These oxygen vacancies drift easily in the film when a voltage is applied in the SET process and prefer to form a line defect perpendicular to the film surface. An isolated oxygen vacancy makes little contribution to the conductivity of Zn O,whereas the ordering of oxygen vacancies in the direction perpendicular to the film surface leads to a dramatic enhancement of the conductivity and thus forms conductive filaments. The semiconducting characteristics of the conductive filaments are confirmed experimentally.

Effect of Blending Ratio on Properties of Core Yarn and Fabric of Polysulfonamide(PSA)/Flame Retardant Viscose(FRV)/Conductive Filament

In order to develop a fabric with excellent flame resistance function,antistatic function,moisture absorption and breathability,the polysulfonamide(PSA)fiber and the flame retardant viscose(FRV)fiber were blended.Meanwhile,the conductive filaments were used as the core yarn,and then they were made into the core-spun yarn and the fabric at different blending ratios of PSA/FRV.The effects of the blending ratio of PSA/FRV on the mechanical properties and the evenness of the yarn were studied.The effects of the blending ratio of PSA/FRV on mechanical properties,flame retardant properties,antistatic properties,moisture permeability and drape of the fabric were analyzed.With the increase of the blending ratios of PSA/FRV,the strength and the elongation of the core-spun yarn increased firstly and then decreased.Moreover,the evenness of the core-spun yarn was improved,the fabric strength increased firstly and then decreased,the flame resistance decreased,and the antistatic performance improved.These results provide an important basis for the preparation and wide application of fabrics made of PSA/FRV/conductive filament.

Improved resistive switching stability of Pt/ZnO/CoO_x /ZnO/Pt structure for nonvolatile memory devices

For Pt(Ag)/ZnO single-layer/Pt structure,random 10 formation and rupture of conductive filaments composed by oxygen vacancies or metallic ions often cause dispersion problems of resistive switching(RS)parameters,which is disadvantageous to devices application.In this study,ZnO/CoOx/ZnO(ZCZ)tri-layers were utilized as the switching layers to investigate their RS properties as compared with ZnO-based single-layer devices.It is interestingly noted that Pt/ZCZ/Pt devices show quite stable bipolar RS behaviors with little resistance value fluctuations compared to Ag/ZCZ/Pt devices and Pt(Ag)/ZnO/Pt devices,which minimize the dispersion of the resistances of RS.This highly stable RS effect of Pt/ZCZ/Pt structure would be promising for high density memory devices.

Effects of different dopants on switching behavior of HfO_2-based resistive random access memory

In this study the effects of doping atoms （AI, Cu, and N） with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory （RRAM） are systematically investigated. The results show that forming voltages and set voltages of A1/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants： oxygen vacancy （Vo） filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.

Resistive switching characteristics of Ti/ZrO_2/Pt RRAM device

In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory de- vices. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament composed of oxygen vacancies. The conduction mechanisms for low and high resistance states are dominated by the ohmic conduc- tion and the trap-controlled space charge limited current （SCLC） mechanism, respectively. The effect of a set compliance current on the switching parameters is also studied： the low resistance and reset current are linearly dependent on the set compliance current in the log-log scale coordinate; and the set and reset voltage increase slightly with the increase of the set compliance current. A series circuit model is proposed to explain the effect of the set compliance current on the resistive switching behaviors.

Current-dependent positive magnetoresistance in La_(0.8)Ba_(0.2)MnO_(3)ultrathin films

We report an investigation into the magnetoresistance(MR)of La_(0.8)Ba_(0.2)MnO_(3)ultrathin films with various thicknesses.While the 13 nm-thick film shows the commonly reported negative magnetoresistive effect,the 6 nm-and 4 nm-thick films display unconventional positive magnetoresistive(PMR)behavior under certain conditions.As well as the dependence on the film's thickness,it has been found that the electrical resistivity and the PMR effect of the thinner films are very dependent on the test current.For example,the magnetoresistive ratio of the 4 nm-thick film changes from+46%to-37%when the current is increased from 10 nA to 100 nA under 15 kOe at 40 K.In addition,the two thinner films present opposite changes in electrical resistivity with respect to the test current,i.e.,the electroresistive(ER)effect,at low temperatures.We discuss the complex magnetoresistive and ER behaviors by taking account of the weak contacts at grain boundaries between ferromagnetic metallic(FMM)grains.The PMR effect can be attributed to the breaking of the weak contacts due to the giant magnetostriction of the FMM grains under a magnetic field.Considering the competing effects of the conductive filament and local Joule self-heating at grain boundaries on the transport properties,the dissimilar ER effects in the two thinner films are also understandable.These experimental findings provide an additional approach for tuning the magnetoresistive effect in manganite films.

Versatile memristor implemented in van der Waals CuInP_(2)S_(6)

Memristors are playing an increasingly important role in developing in-memory computing.Versatile memristors which offer both volatile and non-volatile performances can be employed as both memories and selectors,displaying unique advantages for developing novel electronic circuits.Herein,the remarkable multifunctional memristor with switchable operating modes between volatile and non-volatile by regulating compliance currents is implemented in Ag/CIPS/Au(CIPS:CuInP_(2)S_(6))device.Diode-like volatile memristor performances with the rectification ratio of 10^(3) and an endurance of 500 switching cycles were obtained.Meanwhile,significant non-volatile memory performances with on/off ratio of 10^(3)and retention up to 10^(4)s were also developed,which enables it to be utilized as selectors and memories simultaneously.Moreover,such versatile memristor can emulate the short-term plasticity(STP)and long-term plasticity(LTP)of artificial synapse,demonstrating its advantages in neuromorphic computing applications.

Vertical‐organic‐nanocrystal‐arrays for crossbar memristors with tuning switching dynamics toward neuromorphic computing

Memristors proposed by Leon Chua provide a new type of memory device for novel neuromorphic computing applications.However,the approaching of distinct multi‐intermediate states for tunable switching dynamics,the con-trolling of conducting filaments(CFs)toward high device repeatability and reproducibility,and the ability for large‐scale preparation devices,remain full of challenges.Here,we show that vertical‐organic‐nanocrystal‐arrays(VONAs)could make a way toward the challenges.The perfect one‐dimensional structure of the VONAs could confine the CFs accurately with fine‐tune resistance states in a broad range of 103 ratios.The availability of large‐area VONAs makes the fabrication of large‐area crossbar memristor arrays facilely,and the analog switching characteristic of the memristors is to effectively imitate different kinds of synaptic plasticity,indicating their great potential in future applications.

Physical Mechanism and Performance Factors of Metal Oxide Based Resistive Switching Memory:A Review

This review summarizes the mechanism and performance of metal oxide based resistive switching memory. The origin of resistive switching （RS） behavior can be roughly classified into the conducting filament type and the interface type. Here, we adopt the filament type to study the metal oxide based resistive switch- ing memory, which considers the migration of metallic cations and oxygen vacancies, as well as discuss two main mechanisms including the electrochemical metallization effect （ECM） and valence change memory effect （VCM）. At the light of the influence of the electrode materials and switching layers on the RS char- acteristics, an overview has also been given on the performance parameters including the uniformity, endurance, the retention, and the multi-layer storage. Especially, we mentioned ITO （indium tin oxide） electrode and discussed the novel RS characteristics related with ITO. Finally, the challenges resistive random access memory （RRAM） device is facing, as well as the future development trend, are expressed.

Recent advances in resistive random access memory based on lead halide perovskite

Lead halide perovskites have attracted increasing attention in photovoltaic devices,light-emitting diodes,photodetectors,and other fields due to their excellent properties.Besides optoelectronic devices,growing numbers of studies have focused on the perovskite-based electrical devices in the past few years,such as transistors and resistive random access memories(RRAMs).Here,this article summarizes the recent progress the researchers have made of RRAM devices.Primarily,the working mechanism and the key parameters of RRAM are introduced.Generally,the working principles,including the conductive filament model(containing the types of the model of the metal cationsinduced filament and the model of the ions migration in bulk),the interface effect,and the electronic effect are the origins of the RRAM behaviors,and hence,various factors that affect the device performance are explored.Then,RRAMs based on organolead halide perovskite and all-inorganic perovskite are discussed in terms of different structures,different compositions,and different fabrication methods.Finally,a brief conclusion and a broad outlook are given on the progress and challenges in the field of perovskite-based RRAMs.

Characteristics of HfO_2/Hf-based bipolar resistive memories

Nano-scale Hf/HfO2-based resistive random-access-memory （RRAM） devices were fabricated. The cross-over between top and bottom electrodes of RRAM forms the metal-insulator-metal sandwich structure. The electrical responses of RRAM are studied in detail, including forming process, SET process and RESET process. The correlations between SET voltage and RESET voltage, high resistance state and low resistance state are dis- cussed. The electrical characteristics of RRAM are in a strong relationship with the compliance current in the SET process. The conduction mechanism ofnano-scale Hf/HfO2-based RRAM can be explained by the quantum point contact model.

Resistive switching characteristics of Ni/HfO_2/Pt ReRAM

This study investigated the resistive switching characteristics of the Ni/HfCVPt structure for nonvolatile memory application.The Ni/HfO_2/Pt device showed bipolar resistive switching（RS） without a forming process, and the formation and rupture of conducting filaments are responsible for the resistive switching phenomenon.In addition,the device showed some excellent memory performances,including a large on/off ratio（〉 3×10~5）,very good data retention（〉 10~3 s @ 200℃） and uniformity of switching parameters.Considering these results,the Ni/HfO_2/Pt device has the potential for nonvolatile memory applications.

Metal dopants in HfO_2-based RRAM: first principle study

Based on density-functional theory （DFT）, the effects of metal dopants in HfO2-based RRAM are studied by the Vienna ab initio simulation package （VASP）, Metal dopants are classified into two types （interstitial and substitutional） according to the formation energy when they exist in HfO2 cell. Several conductive channels are observed through the isosurface plots of the partial charge density for HfO2 doped with interstitial metals, while this phenomenon cannot be found in HfO2 doped with substitutional metals. The electron density of states （DOS） and the projected electron density of states （PDOS） are calculated and analyzed; it is found that the conduction filament in HfO2 is directly formed by the interstitial metals and further, that the substitutional metals cannot directly generate conduction filament. However, all the metal dopants contribute to the formation of the oxygen vacancy （Vo） filament. The formation energy of the Vo and the interaction between metal dopants and Vo are calculated; it is revealed that the P-type substitutional metal dopants have a strong enhanced effect on the Vo filament, the interstitial metal dopants have a minor assistant effect, while Hf-like and N-Woe substitutional metal dopants have the weakest assistant effect.

Resistive switching characteristic of electrolyte-oxide-semiconductor structures

The resistive switching characteristic of SiO2 thin film in electrolyte-oxide-semiconductor （EOS） struc- tures under certain bias voltage is reported. To analyze the mechanism of the resistive switching characteristic, a batch olEOS structures were fabricated under various conditions and their electrical properties were measured with a set of three-electrode systems. A theoretical model based on the formation and rupture of conductive filaments in the oxide layer is proposed to reveal the mechanism of the resistive switching characteristic, followed by an experimental investigation of Auger electron spectroscopy （AES） and secondary ion mass spectroscopy （SIMS） to verify the proposed theoretical model. It is found that different threshold voltage, reverse leakage current and slope value features of the switching I-V characteristic can be observed in different EOS structures with different elec- trolyte solutions as well as different SiO2 layers made by different fabrication processes or in different thicknesses. With a simple fabrication process and significant resistive switching characteristic, the EOS structures show great potential for chemical/biochemical applications.