Conductive Filament Research Articles

Novel 3D printed single electrode-based portable and miniaturized electrochemiluminescence platform to detect lactate from human serum

In low- and middle-income countries, three-dimensional printing (3DP) microfluidic devices have demonstrated their potential to be employed in a variety of point-of-care testing applications. This is due to the fact that they offer many advantages over traditional fabrication techniques, like rapid response, easy integration with miniaturized systems, requiring less sample volume, fast prototyping and cost-effectiveness. To the best of our knowledge for the first time, a novel 3D printed single electrode based electrochemiluminescence (3DP-SE-ECL) sensing device was fabricated and utilized to detect various analytes. To fabricate the 3DP-SE-ECL device, the commercially available conductive filaments, like graphene and carbon, were used and an in-depth analysis was performed by sensing H2O2. Furthermore, in order to validate the analytical performance, the best conductive material (graphene filament) was chosen to realize the optimized 3DP-SE-ECL platform, which was validated for lactate sensing. To detect the electrochemiluminescence signal, two approaches were used, first using photomultiplier tube (PMT) and the second by using a smartphone. The lactate concentration was changed from 100 to 7000 µM and a linear range was obtained from 100 to 1000 µM using both PMT and smartphone. Further, the limit of detection was measured to be 6.47 µM and 5.33 µM by smartphone and PMT respectively. To validate the practical usability of 3DP-SE-ECL, real sample analysis of lactate with standard spiking method was performed with excellent recovery rate. Overall, the fabricated 3D-SE-ECL device has the possibilities to be used for a variety of applications, including biomedical and environmental monitoring.

A Numerical Analysis of the Thermal Energy Storage Based on Porous Gyroid Structure Filled with Sodium Acetate Trihydrate

The present paper deals with the evaluation of the unique design of the thermal energy storage unit and its impact on the overall heat exchange efficiency. The proposed thermal energy storage unit consists of a gyroid thermally conductive structure, the voids of which are filled with sodium acetate trihydrate. The presented concept is focused on the use in the field of heavy machinery, where it is possible to accumulate and re-use waste heat from internal combustion engines from the cooling liquid or lubricating products. The evaluation of designs took place through numerical simulations on three models characterized by different levels of the introduction of the gyroid structure into the design. From the design point of view, the gyroid structure was considered as an object produced by additive manufacturing methods from a thermally conductive filament based on a thermoplastic polymer, which enables considerable simplification of production compared to the use of suitable anti-corrosion metals. A comparison of the essential thermophysical parameters in the process of charging and discharging of the proposed thermal energy storage unit quantified a significant increase in the rate of the charging, respectively, of the discharging process, manifested by a rapid increase in the temperature of the sodium acetate trihydrate volume, respectively, of the output temperature of the heat transfer medium that removes the accumulated heat for further use.

Enhancement of Resistive Switching Performance in Hafnium Oxide (HfO2) Devices via Sol-Gel Method Stacking Tri-Layer HfO2/Al-ZnO/HfO2 Structures.

Resistive random-access memory (RRAM) is a promising candidate for next-generation non-volatile memory. However, due to the random formation and rupture of conductive filaments, RRMS still has disadvantages, such as small storage windows and poor stability. Therefore, the performance of RRAM can be improved by optimizing the formation and rupture of conductive filaments. In this study, a hafnium oxide-/aluminum-doped zinc oxide/hafnium oxide (HfO2/Al-ZnO/HfO2) tri-layer structure device was prepared using the sol-gel method. The oxygen-rich vacancy Al-ZnO layer was inserted into the HfO2 layers. The device had excellent RS properties, such as an excellent switch ratio of 104, retention of 104 s, and multi-level storage capability of six resistance states (one low-resistance state and five high-resistance states) and four resistance states (three low-resistance states and one high-resistance state) which were obtained by controlling stop voltage and compliance current, respectively. Mechanism analysis revealed that the device is dominated by ohmic conduction and space-charge-limited current (SCLC). We believe that the oxygen-rich vacancy concentration of the Al-ZnO insertion layer can improve the formation and rupture behaviors of conductive filaments, thereby enhancing the resistive switching (RS) performance of the device.

Evolution between CRS and NRS behaviors in MnO2@TiO2 nanocomposite based memristor for multi-factors-regulated memory applications

Capacitive-coupled memristive effect provides a favorable way for developing novel multifunctional device since it simultaneously exhibits capacitive behavior and resistive switching (RS) effect. Herein, the memristive device with an Ag/MnO2@TiO2/FTO sandwich structure was fabricated, in which the MnO2@TiO2 nanocomposite with different thicknesses was deposited on F-doped SnO2 (FTO) substrates by hydrothermal method. It was observed that the device exhibits the evolution between capacitive-coupled RS (CRS) effect and negative differential resistance (NDR)-coupled RS (NRS) effect by tuning the MnO2 thickness and applied voltage. Through in-depth mechanistic analysis, it was inferred that the evolution behaviors are attributed to the interaction of ions and electrons in the MnO2@TiO2 nanocomposite. With the dielectric capacity of the functional layer increases, the migration of ions and electrons is hindered, which impairs the formation of conductive filaments (CFs), causing a large number of electrons/ions to collect on the interfaces of the functional layer/electrodes, resulting in an internal electric field, thereby observing a macroscopic capacitive effect. Therefore, this work provides a deep understanding of the evolution between CRS and NRS effects, opening a new way for building ultra-low-power multifunctional device for artificial intelligence applications.

Reliable BiI3-Based Resistive Random-Access Memory Devices with a High On/Off Ratio

In this paper, we report resistive random-access memory (RRAM) with bismuth iodide (BiI3) as the resistance switching layer, which exhibits an on/off ratio of the order of 108. The behaviors of the resistive switching performance of the BiI3 devices were systematically investigated. The chemical states and electronic structures of the resistance switching layer (BiI3) were studied via X-ray photoemission spectroscopy with depth profile. The spectroscopies demonstrate that the filament formation belongs to the metal bridge type, which is dominated by the presence of bismuth atoms resulting from the formation of silver iodide (AgI). X-ray diffraction, the cross section of transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were employed to study the formation process of the metal filament in the BiI3-based RRAM. The results reveal that the upward diffusion of Ag cations will react with iodide anions, and bismuth cations will turn into the metallic state, which results in forming a conductive filament inside the resistance switching layer. Furthermore, the devices with the structure of Ag/polymethylmethacrylate (PMMA)/BiI3/PMMA/Au demonstrate low first reset voltage (approximately −0.66 V), a high retention larger than 5 × 104 s, and 6 × 103 switching cycles. This study not only demonstrates the excellent performance of BiI3-based RRAM devices but also provides fundamental insights into the mechanisms of the metallic filament first reset process in the BiI3 layers.

Electrical characteristics and conductive mechanisms of AlN-based memristive devices

Aluminum nitride (AlN) memristive devices have attracted a great deal of attention because of their compatibility with the CMOS fabrication technology, and more likely to be extended to power electronic devices. However, the conductive mechanism and the variability of resistance switching (RS) parameters are major issues for commercial applications. In this paper, we have obtained electrical characteristics of the Al/AlN/Pt memristors under the current compliance limits of 1 𝜇𝜇𝜇𝜇 and 10 𝜇𝜇𝜇𝜇, respectively. Furthermore, the statistics of switching parameters has been done in the Set and Reset processes. Finally, a quantum point contact model has been developed to account for conducting mechanisms and shows the evolution of the conductive filament during RS transitions.

A Highly Crystalline Single Layer 2D Polymer for Low Variability and Excellent Scalability Molecular Memristors.

Large-scale growth of highly crystalline single layer 2D polymers (SL-2DPs) and their subsequent integration into memristors is key to advancing the development of high-density data storage devices. However, leakage problems resulting from the porous structure of 2DPs continue to make such advances extremely challenging. Herein,weovercome this issue by incorporating long alkoxy chains into key molecular building blocks to obtain a highly crystalline 2DP, as visualized by scanning tunneling microscopy, and prevent metal permeation in the subsequent device fabrication process. SL-2DP memristors constructed via direct evaporation of the top electrodes exhibit low variability (σVset = 0.14) due to the single-monomer-thick feature together with the high regular structure and coordination ability which minimizes the stochastic spatial distribution of conductive filaments (CFs) in both vertical and lateral dimensions. The variability is further decreased to 0.04 by confining the formation and fracture of CFs to the interface through the utilization of bilayer junctions. Using peak force tunneling atomic force microscopy, the nanometer scalability (< 50 nm2 ) and low power consumption of these molecular memristor devices are demonstrated.

Nanoscale and ultra-high extinction ratio optical memristive switch based on plasmonic waveguide with square cavity.

A resistive switch effect-based optical memristive switch with an ultra-high extinction ratio and ultra-compact size working at 1550nm is proposed. The device is composed of a metal-insulator-metal waveguide and a square resonator with active electrodes. The formation and rupture of conductive filaments in the resonant cavity can alter the resonant wavelength, which triggers the state of the optical switch ON or OFF. The numerical results demonstrate that the structure has an ultra-compact size (less than 1µm) and ultra-high extinction ratio (37dB). The proposed device is expected to address the problems of high-power consumption and large-scale optical switches and can be adopted in optical switches, optical modulation, optical storage and computing, and large-scale photonic integrated devices.

Influence of the Position of Local Ta Doping in SiNx Resistive Random Access Memory

This article presents an analysis of the effect of the Ta‐doping position on the performance of SiNx‐based resistive random access memories by comparing the electrical properties and conduction mechanisms of the devices. The electrical test results show that when the doping position moves down in the resistive switching (RS) layer, the resistance window of the device increases during the resistive switch process. However, the consistency of the parameter distribution decreases. The conduction mechanism of all Ta‐doped devices behaves as space charge limited current. According to the analysis of the RS model of the device, Ta in the RS layer connects and disconnects with the localized conductive filaments. The adjustment ability of the doping layer on the conductive channel and the reduction of the device stability when the doping position moves up are proposed. Proper Ta doping in the middle of the RS layer of the device allows the device to obtain a large resistance window with relatively stable characteristics.

Forming-Free Tunable Analog Switching in WOx/TaOx Heterojunction for Emulating Electronic Synapses.

In this work, the sputtered deposited WOx/TaOx switching layer has been studied for resistive random-access memory (RRAM) devices. Gradual SET and RESET behaviors with reliable device-to-device variability were obtained with DC voltage sweep cycling without an electroforming process. The memristor shows uniform switching characteristics, low switching voltages, and a high RON/ROFF ratio (~102). The transition from short-term plasticity (STP) to long-term potentiation (LTP) can be observed by increasing the pulse amplitude and number. Spike-rate-dependent plasticity (SRDP) and paired-pulse facilitation (PPF) learning processes were successfully emulated by sequential pulse trains. By reducing the pulse interval, the synaptic weight change increases due to the residual oxygen vacancy near the conductive filaments (CFs). This work explores mimicking the biological synaptic behavior and further development for next-generation neuromorphic applications.

Controlling Threshold and Resistive Switch Functionalities in Ag‐Incorporated Organometallic Halide Perovskites for Memristive Crossbar Array

AbstractHalide perovskites (HPs) can be the effective functional materials for the sneak‐path current issue in the memristive crossbar array. Herein, an efficient strategy is proposed to integrate the HPs‐based bidirectional threshold and bipolar resistive switches (TS and RS). The resistance change characteristics from volatile threshold to nonvolatile resistive switching are modulated by controlling Ag doping concentration in the MAPbI3. HPs provide the diffusive condition and the quantity of Ag regulates the radius of its network. A low amount of Ag contributes to weak network with a short lifetime. However, when the amount of Ag increases, the conductive filament becomes more robust, showing a long lifetime. A MAPbI3:Ag TS with a low Ag content is developed, showing a steep switching slope (1 mV per decade), fast switching speed (&lt; 80 ns), and low off‐current (10 nA). And, a MAPbI3:Ag RS with a high Ag content is developed, showing multilevel storage capability and long retention time (1400 s). Finally, these TS and RS coupled into the 1S‐1R integrated component, resulting the development of the maximum crossbar array size to 1.4 × 1012. This study offers an efficient methodology for tailoring the resistance change characteristics and a promising strategy for practical HPs‐based memristive crossbar application.

MoTe2-based low energy consumption artificial synapse for neuromorphic behavior and decimal arithmetic

Two-dimensional material-based memristors have shown attractive research prospects as brain-like devices for neuromorphic computing. Among them, transition metal dichalcogenides–based memristors have proved to be one of the most promising competitors. In this work, a two-dimensional memristor based on MoTe2 nanosheets was fabricated and demonstrated. The experimental results illustrate that the two-terminal synaptic based on the Ag/MoTe2/ITO structure exhibits stable bipolar and non-volatile resistive switching characteristics attributed to the controllable formation and rupturing of silver conductive filaments. The device can be successively modulated by a pulse train with a minimum pulse width of 40 ns. More interestingly, the energy consumption of the device to complete one write event is only 74.2 pJ. In addition, biological synaptic behaviors, such as excitatory postsynaptic current gain properties, long-term potentiation (LTP)/long-term depression, spike-timing-dependent- plasticity, short-term plasticity, long-term potentiation (LTP), paired-pulse facilitation, post-tetanic potentiation, and learning-experimental behaviors were mimicked faithfully. Finally, the decimal arithmetic application was introduced to the device, and it is confirmed that addition and multiplication functions can be performed. Therefore, the artificial synapse based on MoTe2 nanosheets not only exhibits the stable non-volatile resistive switching behavior but also facilitates the development of low-energy consumption neuromorphic computing chips based on transition metal dichalcogenides.

Optoelectronic Resistive Memory Based on Lead‐Free Cs2AgBiBr6 Double Perovskite for Artificial Self‐Storage Visual Sensors

AbstractMimicking the human visual memory system has attractive prospects in the field of artificial vision. However, the prominent challenge of realizing human visual memory is how to detect and store image information at the same time, which demands a multifunctional electronic device that can sense and memorize image information like the brain. In this work, simple two‐terminal optoelectronic resistive random access memory (ORRAM) devices are demonstrated based on lead‐free Cs2AgBiBr6 perovskite, exhibiting a unique optoelectronic resistive characteristic that can be reset by UV light illumination. A proof‐of‐concept artificial self‐storage visual system based on the ORRAM is constructed, which shows similar reinforcement learning and memory forgetting functions to the human visual memory system, and realizes the integrated functions of image sensing and memory for a long‐term retention time (&gt;6000 s). Theoretical calculations indicate that UV light illumination will induce the annihilation of Br defects and cause the fracture of conductive filaments, resulting in the optical RESET phenomenon. Furthermore, by integrating with perovskite solar cells, an all‐optically controlled universal implication logic gate is constructed. This work provides an important step toward the mimicry of human visual memory and the multifunctional artificial visual integration of perception and storage.

A memristor based on two-dimensional MoSe2/MoS2 heterojunction for synaptic device application

Two-dimensional materials are promising for exploring memristors with excellent performance. However, the memristor still faces challenges in insufficient reliability due to resistance-switching mechanisms of conductive filaments. In this work, a typical metal/heterojunction/metal structure (Ag/MoSe2/MoS2/Au/Ti) was proposed as the device architecture of the memristor. The device exhibits stable bipolar resistive switching behavior with a high on–off ratio, long retention time, and good endurance. The resistance-switching is achieved by adjusting the interface barrier of the MoSe2/MoS2 due to the band modulation. Moreover, we explore the essential synaptic functions of this memristor device, with outstanding voltage pulse potentiation and depression. Our work highlights the significant prospects of MoSe2/MoS2 heterojunction in artificial synapses and neural networks.

Ultralow-Power RRAM with a High Switching Ratio Based on the Large van der Waals Interstice Radius of TMDs.

Low power and high switching ratio are the development direction of the next generation of resistive random access memory (RRAM). Previous techniques could not increase the switching ratio while reducing the SET power. Here, we report a method to fabricate low-power and high-switching-ratio RRAM by adjusting the interstice radius (rg) between the van der Waals (vdW) layers of transitional-metal dichalcogenides (TMDs), which simultaneously increases the switching ratio and reduces the SET power. The SET voltage, SET power, switching ratio and endurance of the device are strongly correlated with rg. When the ratio of rg to the radius of the metal ions that form the conductive filaments (rg/rAg+) is near 1, the SET voltage and SET power vertically decrease while the switching ratio vertically rises with increasing rg/rAg+. For the fabricated Ag/[SnS2/poly(methyl methacrylate)]/Cu RRAM with an rg/rAg+ of 1.04, the SET voltage, SET power and switching ratio are 0.14 V, 10-10 W and 106, respectively. After 104 switching cycles and a 104 s retention time, the switching ratio of the device can still be stable above 106. Bending has no influence on the performance of the device when the bending radius is not <2 mm.

Recycled Additive Manufacturing Feedstocks for Fabricating High Voltage, Low‐Cost Aqueous Supercapacitors

AbstractThe first recycled conductive poly(lactic acid) (PLA) filament derived from post‐industrial waste sources for additive manufacturing (AM) is reported herein, presenting a paradigm shift in plastic waste recycling, AM filament production, and AM energy storage architectures. Filaments utilizing a base of recycled PLA, carbon black (CB) as a conductive filler, and polyethylene glycol (PEG) as a plasticizer are used to produce aqueous AM symmetric supercapacitor platforms that can reach capacitance values 75 times higher than commercially available conductive PLA filaments. Furthermore, through the rapid prototyping capabilities of AM and GCode modification, it is seen that changing the electrode architecture from solid to a mesh with additional inter‐layer spacing is able to further enhance electrode performance by 3.5 times due to improvements in the surface area, ion accommodating capabilities, and faster ion diffusion. The symmetric full cell device is capable of delivering 7.82 mF cm−2, 4.82 µWh cm−2, and 433.32 µW cm−2 of capacitance, energy, and power density, respectively. Moreover, the material cost is £0.15 per electrode. This study represents a new direction for plastic waste recycling, in which low‐value recycled base products can be manufactured into high‐value end products in their second cycles.

Suppressing the filament formation by aluminum doping in anatase titanium oxide

For a resistance random access memory whose insulating matrix is based on transition metal oxides, the underlying microscopic mechanism of its conductive filaments is crucial yet challenging to understand. In this paper, our first-principles calculations predict that titanium oxide prefers its anatase phase over rutile either with or without aluminum doping. We report that an oxygen vacancy in the anatase titanium oxide is stable in its neutral charge state when free of an external field, while it is unstable in the singly and doubly charged states. By calculating the dissociation energy of a single vacancy from a conductive filament, we also study the filament rupture that is modeled by an array of oxygen vacancies, with or without a nearby aluminum dopant. We find that for the dopants at a specific site, the conductive filaments tend to disconnect, which, in turn, enhances the endurance of a non-filamentary resistance random access memory.

Multifunctional flexible conductive filament for human motion detection and electrothermal

Highly sensitive wearable e-textiles play an important role in flexible sensors and next-generation personalized electronics with application potential in human physiological monitoring, environmental monitoring, and electronic skin. Here, a scalable and simple strategy for preparing liquid metal (LM)/carbon nanotubes (CNTs)@Ecoflex (LCEF) coaxial conductive filaments were fabricated by wet spinning. The electro-mechanical response behaviors of LCEF sensors were explored to evaluate their sensitivity and stability. The results demonstrated that the filament strain sensors could be used for monitoring both large and subtle human motions. Besides, the LCEF fabrics as a large-area flexible heater exhibited efficient electrothermal response, evidenced by achieving a temperature of over 112.1 °C upon applying a voltage of 12 V with 52.6 °C obtained on the fabrics within 42 s. This work may shed lights on scalable fabrication of flexible strain sensors and electrothermal devices which pave the way for the development of multifunctional wearable electronic devices.

Fermi-Level Pinning Engineering for Achieving High-Performance Ge-Based Resistive Memory With Ultrahigh Self-Rectifying Ratio (&gt; 105)

In this work, we investigate the self-rectifying behaviors of the resistive random access memory (RRAM) fabricated on n-Ge substrates, featuring an ultrahigh rectifying ratio (> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{5}}$ </tex-math></inline-formula> ), a high ON/ OFF ratio (>500), and low operation voltages. The excellent performances of the Ge-based RRAM in this study are attributed to the Fermi-level pinning (FLP) near the valence band edge of n-Ge through the localized conductive filaments in HfO2. In addition, the underlying mechanism of the FLP behaviors in RRAM on n-Ge substrates is discussed. The electrical properties of the self-rectifying RRAM, including superior data retention, excellent uniformity, decent switching speed, endurance, and robust read/write disturbance immunity, are characterized comprehensively. The FLP-induced superior rectifying behaviors and excellent electrical properties of the RRAM enable the potential application of the high-density nonvolatile memory.

Study on ion dynamics of hafnium oxide RRAM by electrode thermal effect

Resistive random access memory (RRAM) has become one of the representatives of the next generation of nonvolatile memory because of its excellent performance, and the data reading function is caused by the growth and fracture of the conductive filament (CF) in the switch layer. Therefore, the study of the thermal properties of materials on the conductive mechanism is a step that cannot be ignored. In this paper, a numerical model of filament dissolution caused by the coupling effect of Joule heat and electric field in resistance elements is established. The influence of the thermal field on the electric field and ion mobility during device setup and reset is explained by solving partial differential equations. On this basis, the importance of electrode parameters for resistive switching behavior is emphasized. The results show that the best performance can be obtained at 298 K when TiN is selected as the top electrode material of the equipment. This work has deepened the understanding of RRAM resistance switch characteristics and has guiding significance for selecting memristor materials and promoting its industrialization process.