Conductive Bridge Research Articles

Sulfur-doped graphene promoted Li4Ti5O12@C nanocrystals for lithium-ion batteries

Herein, sulfur-doped graphene modified Li 4 Ti 5 O 12 @C nanocomposite (SG-T@C) has been firstly fabricated via a sol-gel method assisted with solid-state route. In this composite, the Li 4 Ti 5 O 12 @C nanocrystals (T@C) are homogeneously dispersed into the two-dimensional sulfur-doped graphene. The introduced sulfur-doped graphene acted as conductive bridge within the resulted nanocomposite, thereby enhancing the electrical conductivity of T@C nanoparticles. The as-fabricated SG-T@C displays superior high-rate performance for lithium-ion batteries. It can deliver the capacities of 171.9 and 145.2 mAh/g at 0.1 and 10 C respectively. Besides, SG-T@C exhibits 96.2% capacity retention at 20 C over 800 cycles, demonstrating an excellent cycling stability. Therefore, the designed SG-T@C can be used as an advanced electrode for lithium-ion batteries. • Sulfur-doped graphene-improved Li 4 Ti 5 O 12 @C nanocomposite has been fabricated for the first time through a simple sol-gel method. • The constructed conductive networks by sulfur-doped graphene sheets and carbon film can greatly enhance the apparent electrical conductivity of Li 4 Ti 5 O 12 . • The fabricated anode displays superior rate capability for lithium-ion storage.

Versatile GeS-based CBRAM with compliance-current-controlled threshold and bipolar resistive switching for electronic synapses

Chalcogenide materials have promising physical and electrical characteristics for use in advanced memory and electronic synaptic devices. However, limited research has been conducted on chalcogenide materials for highly advanced and scalable memory devices. In this study, we investigate compliance current (CC)-controlled resistive switching (RS) in a monochalcogenide GeS-based conductive bridge random access memory (CBRAM) device for use in advanced memory and electronic synapses. A CBRAM device with a structure stacking sequence of Ag/GeS/Pt/Ti/SiO2 is fabricated by depositing a 13 nm GeS layer using a sputtering process. The GeS-based CBRAM device exhibits the reversible CC-controlled transition between threshold resistive switching (T-RS) and bipolar resistive switching (B-RS). Under a high CC (1 mA and above), the device exhibits B-RS behavior with excellent retention and highly reproducible endurance characteristics, illustrated by a very high ION/IOFF ratio of almost ∼2 × 108. Under a low CC (100 µA and below), the device exhibits T-RS, with the automatic transition from a low resistance state (LRS) to a high resistance state (HRS) when sweeping the voltage in the reverse direction. Under all CC conditions, the device has a very low HRS current of around ∼1 × 10−12 A. A model based on the formation and rupture of conductive filaments (CFs) is proposed to explain the coexistence of T-RS and B-RS in GeS-based CBRAM devices. In particular, the change in the size and geometry of the CFs in accordance with the applied CC is speculated to be the main reason for the coexistence of T-RS and B-RS. The retention characteristics of the device in both T-RS and B-RS mode are investigated for possible application to case-sensitive hardware-based data security and the disposal of trusted and untrusted information. The ability of the CBRAM device in T-RS mode to perform important biological synaptic functions for potential use in brain-inspired neuromorphic systems is also investigated.

Emulating low power nociceptive functionalities with a forming-free SiO2/VOx conductive bridge memory with Pt nanoparticles

The fabrication of low-power and scalable electronic devices that will have the ability to emulate the properties of the biological nociceptors is of great importance for the development of humanoid robots. Along these lines, in this work, an artificial nociceptive element composed of a SiO2/VOx-based bilayer configuration and a dense layer of Pt nanoparticles (NPs) as a bottom electrode is proposed. Interestingly, the device operates only under the threshold switching mode with the switching voltage as low as ∼220 mV and a huge switching ratio of 107. A systematic analysis of the impact of the bilayer configuration and the existence of the Pt NPs on the total memory performance is also provided, while a comprehensive numerical model is introduced to highlight the crucial role of the electrode material on the local temperature distribution and its influence on the memristive effect. On top of that, the proposed structure can imitate the normal, relaxation, and sensitization states of the nociceptors with about 0.3 pJ energy per spike. These enhanced properties are ascribed to the self-rupture of the Ag-based conducting filament, whereas valuable insights into the impact of the local temperature distribution on the switching dynamics are provided.

An electrochemical sensor based on cobalt oxyhydroxide nanoflakes/reduced graphene oxide nanocomposite for detection of illicit drug-clonazepam

Clonazepam (CNZ) is a commonly prescribed drug for the management of mental illness including insomnia, panic anxiety and status epilepsy. Due to the associated sedative effects, CNZ has also become a drug of abuse amongst addicted users, sexual assault cases, and suicide. Therefore, it becomes vital to analyze CNZ in human specimens for criminal investigational purposes. Herein, we report the construction of an electrochemical sensor based on self-assembled hybrid nanocomposite of 2-D transition metal oxide nanoflakes i.e., cobalt oxyhydroxide (CoOOH) nanoflakes and reduced graphene oxide (rGO) for determination of clonazepam (CNZ), especially in different beverages. The physico-chemical characterization of the as-synthesized hybrid nanocomposite was done by scanning electron microscopy (SEM), X-Ray diffraction (XRD), raman spectroscopy, X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and UV–Visible spectroscopy. Further, the surface of the screen printed carbon electrode (SPCE) was modified with CoOOH-rGO hybrid nanocomposite and its electrochemical characteristics were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. A synergistic combination of CoOOH nanoflakes with abundant catalytic sites and highly supportive skeletons of rGO nanosheets that act as conductive bridges for charge transfer makes the nanocomposite sensor unique for electrochemical detection. Under optimized conditions, the specific interaction of CNZ with CoOOH-rGO modified SPCE was determined by differential pulse voltammetry (DPV) to measure the dose dependent increase in reduction current values at a potential of 0.11 V. The developed sensor achieved a detection limit of 38 nM with a sensitivity of 0.054 µA µM−1 cm−2 over a dynamic concentration range of 0.1–350 µM. Moreover, the sensor was applied for determination of CNZ in spiked beverages samples and showed satisfactory recovery in the range of 87–115%. This work provides a new avenue for the development of hybrid nanocomposites based electrochemical sensing platforms for on-site screening of illicit drugs, as necessitated for forensics and clinical settings.

Nickel hexacyanoferrate incorporated with reduced graphene oxide for highly efficient intercalation desalination

In this study, nickel hexacyanoferrate (NiHCF) was incorporated with reduced graphene oxide (rGO) as a pseudocapacitive intercalation cathode in asymmetric capacitive deionization (ACDI) for desalination. The electrochemical characterization results demonstrated that the NiHCF@rGO nanocomposite exhibited an excellent specific capacitance of 158.2 F g−1 at a scan rate of 5 mV s−1 and high electrical conductivity. The desalination experiments were carried out in single-pass mode for the performance analysis under different operational parameters. For desalting 4 g L−1 NaCl solution at 1.2 V, NiHCF@rGO-assembled ACDI exhibited a large salt adsorption capacity of 80.2 mg g−1 and a high charge efficiency of 86.6%, associated with an energy consumption of 0.053 kWh m−3. It is noted that the NiHCF@rGO-assembled ACDI significantly outperformed the activated carbon-based membrane capacitive deionization for desalination. More importantly, the incorporation of rGO can improve the 27.7% salt adsorption capacity of NiHCF. The significant improvement can be ascribed to rGO uniformly distributing NiHCF particles on its surface via conductive bridges, which enable a low charge transfer resistance and facilitate the transport of ions. The X-ray photoelectron spectroscopy analysis further verified the Na+ intercalation/deintercalation of the NiHCF@rGO electrode, accompanied by the Fe3+ to Fe2+ redox reaction in a cyclic charging–discharging process. Overall, this work demonstrates the great potential of NiHCF@rGO as a cathode for efficiently improving desalination performance.

Water-soluble polyethylene-oxide polymer based memristive devices

In this research work, Conductive bridge Random Access memory devices (CBRAMs) featuring a water-solution processed Polyethylene Oxide (PEO) layer used as solid polymer electrolyte were fabricated. The devices showed promising results with forming-free capabilities, switching voltages within the range from −1.5 V to 2.0 V, high OFF/ON resistance ratio ~ 105 and > 300 cycles each at 10 & 100 μA compliance current (CC). Cycling at various CC also confirmed that the conductive filament was more stable at higher compliance current with a higher probability to achieve non-volatile switching. This article also reports the conduction mechanism in the high and low resistance states for PEO based devices. Finally, due to their high OFF/ON current ratio, it is suggested that these devices could also serve as BEOL (Back-End-Of-Line) selector devices while operating in their volatile mode.

Conductive Bridge Random Access Memory (CBRAM): Challenges and Opportunities for Memory and Neuromorphic Computing Applications.

Due to a rapid increase in the amount of data, there is a huge demand for the development of new memory technologies as well as emerging computing systems for high-density memory storage and efficient computing. As the conventional transistor-based storage devices and computing systems are approaching their scaling and technical limits, extensive research on emerging technologies is becoming more and more important. Among other emerging technologies, CBRAM offers excellent opportunities for future memory and neuromorphic computing applications. The principles of the CBRAM are explored in depth in this review, including the materials and issues associated with various materials, as well as the basic switching mechanisms. Furthermore, the opportunities that CBRAMs provide for memory and brain-inspired neuromorphic computing applications, as well as the challenges that CBRAMs confront in those applications, are thoroughly discussed. The emulation of biological synapses and neurons using CBRAM devices fabricated with various switching materials and device engineering and material innovation approaches are examined in depth.

Effect of conductance linearity of Ag-chalcogenide CBRAM synaptic devices on the pattern recognition accuracy of an analog neural training accelerator

Abstract Pattern recognition using deep neural networks (DNN) has been implemented using resistive RAM (RRAM) devices. To achieve high classification accuracy in pattern recognition with DNN systems, a linear, symmetric weight update as well as multi-level conductance (MLC) behavior of the analog synapse is required. Ag-chalcogenide based conductive bridge RAM (CBRAM) devices have demonstrated multiple resistive states making them potential candidates for use as analog synapses in neuromorphic hardware. In this work, we analyze the conductance linearity response of these devices to different pulsing schemes. We have demonstrated an improved linear response of the devices from a non-linearity factor of 6.65 to 1 for potentiation and −2.25 to −0.95 for depression with non-identical pulse application. The effect of improved linearity was quantified by simulating the devices in an artificial neural network. The classification accuracy of two-layer neural network was seen to be improved from 85% to 92% for small digit MNIST dataset.

Investigation of deposition technique and thickness effect of HfO2 film in bilayer InWZnO-based conductive bridge random access memory

In recent research on memristor of brain-mimicking integrated circuit (IC) architecture, the electrical performance of electrochemical metallization memory can be significantly improved by applying a bilayer switching structure. In this work, a novel amorphous semiconductor InWZnO (IWZO) is used as the main switching layer, and a bilayer structure with HfO2 is fabricated by different deposition technique. By surface and chemical composition analysis, the effect of deposition process and thickness of HfO2 have been fully explored. The bilayer memory inserted with 3 nm HfO2 formed by atomic layer deposition process exhibits excellent electrical properties, such as high endurance cycle (more than 2 × 103), better retention time (up to 2 × 104 s, 85 °C), relatively uniform resistance state distribution and low compliance current operation. Consequently, the low power electrochemical metallization memory with optimized HfO2 layer has great potential for next generation memory in pixel and three-dimensional brain-mimicking IC technology.

A sulfur-doped carbon-enhanced Na3V2(PO4)3 nanocomposite for sodium-ion storage

To promote the electrical conductivity of Na3V2(PO4)3 (NVPO) for sodium-ion storage, sulfur-doped carbon-promoted Na3V2(PO4)3 (NVPO@SC) composite has been firstly fabricated using a sol-gel route assisted with a solid-state reaction process. In this designed cathode material, NASICON-type NVPO nanocrystals are homogeneously coated with a thin sulfur-doped carbon film. The introduced sulfur-doped carbon coating acts as a conductive bridge between NVPO particles, thereby improving the electrical conductivity of NVPO electrode. Compared to the carbon-decorated NVPO (NVPO@C) material, the designed NVPO@SC displays superior sodium storage performance because of its good electrical conductivity. It exhibits the high discharge capacities of 110.3 and 105.9 mAh/g at 0.1 and 2 C respectively and presents a 97.8% capacity retention over 300 cycles at 10 C. Therefore, the resulted NVPO@SC nanocomposite might be a prospective advanced electrode in sodium-ion batteries.

Effect of TiW blocking layer and temperature annealing on resistive switching parameters of Hafnium oxide based CBRAM device

An approach for enhancing the characteristics of resistive switching in the crystalline Hafnium oxide-based CBRAM (Conductive Bridging Resistive Switching Memory) device is reported in this article. The crystalline Hafnium oxide resistive switching layer and the TiW blocking layer are beneficial for controlling filament growth. Improved resistive parameters, including stability and resistance distribution, were successfully demonstrated in Cu/TiW/annealed-HfO2/Pt devices compared to Cu/HfO2/Pt-based devices. Moreover, the proposed bipolar device demonstrates improved memory performance, such as good retention characteristics (>104 s) and a high ON/OFF resistance ratio.

The synergistic effect of micron spherical and flaky silver-coated copper for conductive adhesives to achieve high electrical conductivity with low percolation threshold

In the application of electronic products, it is critical for conductive adhesives to ensure high electrical conductivity and good adhesion reliability. In this study, isotropic conductive adhesives (ICAs) with high conductivity and low percolation threshold can be achieved by making full use of the synergistic effect of micron spherical and flaky silver-coated copper ([email protected]) conductive fillers. The flaky [email protected] powder prepared by electroless plating was chosen as the main conductive filler, and the spherical core-shell structure [email protected] powder was used as an auxiliary conductive filler to be dispersed in the flaky [email protected] particles, providing more possibilities for building a large number of conductive bridges. In this study, the [email protected] powder was synthesized to eliminate the disadvantages of Cu oxidation and Ag electrochemical migration, while making the ICAs low cost and favourable conductivity. Furthermore, the curing parameters were optimized for the matrix resin in corresponding experiments. The results showed that a combination of spherical and flaky [email protected] powders in ICAs could not only significantly reduce the percolation threshold and the bulk resistivity but also increase the shear strength compared with the single component. In particular, the bulk resistivity of the optimum sample was 1.95 × 10−3 Ω cm, and the shear strength was 22.69 MPa when the filler content was only 60 wt%. Hence, the ICAs filled with spherical and flaky [email protected] will pave the way for high-performance and low-cost ICAs in the electronics packaging industry.

A 10-nm-thick silicon oxide based high switching speed conductive bridging random access memory with ultra-low operation voltage and ultra-low LRS resistance

In this paper, a silicon oxide based conductive bridging random access memory (CBRAM) with an ultra-low operation voltage, a high switching speed, and an ultra-low resistance at low resistance state (LRS) is reported. The CBRAM has a sandwich structure with platinum and copper as electrode layers and an ultra-thin 10-nm-thick silicon oxide film as an insulating switching layer. The CBRAMs are fabricated with CMOS compatible materials and processes. DC I–V sweep characterizations show an ultra-low SET/RESET voltage of 0.35 V/−0.05 V, and the RESET voltage is the lowest among all ultra-low voltage CBRAMs. The CBRAM is capable of withstanding endurance tests with over 106 pulses of +0.4 V/−0.1 V with 1 μs pulse width, with the resistance at LRS maintaining at an ultra-low value of only 20 Ω, which is the lowest among all CBRAMs to date, and it is reduced by at least 2.95 times compared with prior studies. Meanwhile, the switching ratio between high resistance state and LRS is more than 1.49 × 104. Moreover, the switching time characterization of the CBRAM demonstrates an ultra-short SET/RESET time of 7/9 ns. The CBRAM has potential applications in high-speed, ultra-low voltage, and ultra-low power electronics.

ZIF-67 derived in-situ grown N–Co3S4-GN/CNT interlinked conductive networks for high-performance especially cycling stable supercapacitors

Transition metal sulfides (TMSs) have become promising candidates as electrode materials in energy storage fields thanks to the high theoretical capacity. However, their application is hindered by depressed electrical conductivity and poor cycling performance. Herein, we proposed a ZIF-67 derived, nitrogen-doped, graphene-coated and carbon nanotubes-interlinked 3D Co3S4/C conductive network (N–Co3S4-GN/CNT) for high-performance supercapacitors. Through controlling the mass ratio of ZIF-67, melamine and g-C3N4, various microstructures with determined electrochemical performance could be achieved. The nanocomposites synthesized with the ingredient mass ratio of 2: 1: 1 (NCSC-211) were proven to have the most excellent comprehensive electrochemical properties. In the NCSC-211 nanostructure, multi-layer graphene function as conductive shells for improved cycling performance by alleviating pulverization caused by volume change, thick CNTs act as conductive bridges and agglomeration spacers that increase electron conductivity and provide more active sites for redox reaction and doped-nitrogen offer enhanced wettability to electrolyte and faster electron transfer. The NCSC-211 electrode displayed specific capacitance of 1158 F g−1 at 1 A g−1, rate capability of 86% at 10 A g−1 and extraordinary cycling stability with 97.2% capacitive retention after 4000 cycles. Furthermore, the assembled asymmetric supercapacitor NCSC-211//activated carbon exhibited energy density of 43.73/37.69 Wh kg−1 at power density of 800/8000 W kg−1 and capacity retention of 95.3% after 5000 cycles at 5 A g−1. The designing strategy of in-situ grown instead of additional added conductive phase that fully-covered and strongly-interlinked network nanostructure may pave the road towards TMSs in synthesizing energy storage materials by compensating their intrinsic drawbacks.

TiO2 nanoparticles coated Co3O4/C microspherical as a high rate lithium storage material

ABSTRACT Regulating the components of anodic materials is an effective strategy for improving their Li-storage performances. Such component control can permit defined electrochemical performances. TiO2 shows good discharge capability at high current density, and it has been applied to modify the electrochemical property of Co3O4/C. In the composite Co3O4/C/TiO2, TiO2 nanoparticles are mainly coated on the surface of Co3O4 micro-particles, and C acts as a conductive bridge. With the assistance of TiO2, the formed heterointerface or pseudocapacitance gives rise to an improved discharge capacity of Co3O4/C/TiO2 at a current density of 2000 mA g−1 without a discharge plateau. the cyclic voltammograms curves and discharge curves show apparent changes after the application of TiO2. The morphologies of the electrode and the active materials change with an increasing number cycles. Nevertheless, the discharge capacity remains stable. This finding indicates that controlling the amount of the active component is effective in improving the Li-storage performance .

CBRAM technology: transition from a memory cell to a programmable and non-volatile impedance for new radiofrequency applications

Electrical resistance control programming of conductive bridging random access memory (CBRAM) radio frequency (RF) switches could benefit the development of electronically controlled non-volatile RF attenuators and other reconfigurable devices. The object of this study is to adapt a conventional CBRAM based memory cell to be used as an RF switch, and to demonstrate the feasibility of programming non-volatile RF CBRAM switches to achieve specific target resistances within a range of continuous values. The memory-RF technologic transition implies a drastic increase of the geometry in order to handle a much higher power, a decrease of the transition capacitance in order to operate at much higher frequencies, and a decrease of the LRS to a few ohms, which is critical for RF applications. These studies are initially performed on an in-house made RF CBRAM cell array at DC frequency, and then extended successfully to a co-planar waveguide (CPW) based shunt mode RF switch with an integrated CBRAM cell. Reliability of the proposed technique is validated through detailed analysis of factors like repeatability of the process, time stability of programmed states, and statistics of time taken to converge to a desired resistance value for an arbitrary RF CBRAM switch.

N-doped graphene quantum dots as charge-transfer-bridge at LaSrCoO/MoSe2 heterointerfaces for enhanced water splitting

A bifunctional electrocatalyst interface requires superior charge transfer and good electrical conductivity to produce a water splitting reaction that is overall efficient and stable. In the context of engineering the interfacial band alignment, we demonstrate a novel and straightforward approach to control the electrochemical activity of the bifunctional catalysts with precision by bridging conductive N-doped graphene quantum dots (N-GQDs, 2–3 nm) between La0.5Sr0.5CoO3–δ (LSC) and MoSe2 interfaces. The N-GQDs govern the charge transfer process at the interface, exhibiting higher Co3+ cations and metallic 1 T-MoSe2 phase-transition compared to those of LSC and LSC-MoSe2 composites. As a result, the optimized LSC-N-GQDs-MoSe2 electrocatalyst possessed a lower overpotential, Tafel slope, and charge transfer resistance in HER and OER than pure and LSC-MoSe2 electrocatalysts in an alkaline solution. The Tafel slopes (64 mV·dec−1 and 51 mV·dec−1 for HER and OER respectively) are smaller than those of current solutions that are commercially available, showing a higher performance at a high current density of 500 mA·cm−2 with a long-term 24 h stability test. The key design of the current study is based on conductive bridging in the bifunctional catalyst to improve the interfacial charge transfer and electrochemical reaction.

Density functional simulations of a conductive bridging random access memory cell: Ag filament formation in amorphousGeS2

Density functional/molecular dynamics simulations have been performed to shed light on the drift of Ag atoms in an amorphous $\mathrm{Ge}{\mathrm{S}}_{2}$ solid-state electrolyte between Ag and Pt electrodes in the presence of a finite electric field. The system models a conductive bridging random access memory device, where the electric field induces the formation of conductive filaments across the chalcogenide. Simulations of a 1019-atom structure under an external electrostatic potential of 0.20 eV/\AA{} at 480 and 680 K show significant atomic diffusion within 500 ps. Ag migration and the formation of percolating filaments occur in both cases. Three simulations for a smaller model (472 atoms) confirm the formation of percolating Ag strings. Significantly reduced mobility of Ag cations at 380 K means that Ag migration to the Pt electrode did not occur within 1 ns. The electronic structure analysis of selected snapshots shows that dissolved Ag atoms become markedly cationic, which changes when Ag clusters form at the Pt electrode. The electrolyte does not conduct, despite percolating single-atom Ag wire segments. Sulfur becomes anionic during the migration as a result of Ag-S bonding, and the effect is most pronounced near the active electrode. The formation of conductive filaments requires a percolating network of Ag clusters to grow from the Pt interface, and the weakest link of this network is at the Ag electrode.

A flexible and sensitive strain sensor with three-dimensional reticular structure using biomass Juncus effusus for monitoring human motions

Flexible strain sensors have received extensive attention owing to their booming development. However, achieving high sensitivity and stretchability simultaneously for strain sensors is still a challenge. Herein, we report a fiber-based stretchable strain sensor with a unique three-dimensional (3D) reticular structure for human motion monitoring. The biomass Juncus effusus (JE) fiber was functionalized with carbon nanotubes (CNTs) and Ecoflex (EF) using a facile dip-coating-drying approach, and a syringe extraction method, respectively. The resulted JE/CNTs/EF fiber strain sensors exhibited advanced performance of strong flexibility, high sensitivity, and multifunctionality, which displayed a superior sensitivity (gauge factor of 24.95–76.79) and high stretchability (600%). Moreover, good repellency to chemicals and stable responses to various stimuli frequencies over 270 cycles were obtained for the as-prepared sensors. The microfibrils of the JE fiber formed a complicated 3D reticular structure acting as the conductive bridges when stretching. Consequently, the fiber-based JE/CNTs/EF strain sensor can not only accurately detect a full range of body motions and subtle signals, but also can be a promising candidate as a Morse code generator for cryptographic communication.

Formation of a ternary oxide barrier layer and its role in switching characteristic of ZnO-based conductive bridge random access memory devices

The insertion of a metal layer between an active electrode and a switching layer leads to the formation of a ternary oxide at the interface. The properties of this self-formed oxide are found to be dependent on the Gibbs free energy of oxide formation of the metal (ΔGf°). We investigated the role of various ternary oxides in the switching behavior of conductive bridge random access memory (CBRAM) devices. The ternary oxide acts as a barrier layer that can limit the mobility of metal cations in the cell, promoting stable switching. However, too low (higher negative value) ΔGf° leads to severe trade-offs; the devices require high operation current and voltages to exhibit switching behavior and low memory window (on/off) ratio. We propose that choosing a metal layer having appropriate ΔGf° is crucial in achieving reliable CBRAM devices.