Threshold Resistive Switching Research Articles

Conversion from memory to threshold resistance switching behavior by modulating compliance current

The volatile and nonvolatile resistance switching (RS) characteristics can be, respectively, used for the selector and memristor, which have received much attention. Thus, it is essential to find a simple and effective method to control the specific RS behavior of NbOx materials due to the co-occurrence of memory RS and threshold RS behaviors. Here, the NbOx film with a thickness of 100 nm was prepared by magnetron sputtering at 80 °C. The tungsten steel tip/NbOx/Pt device exhibited the co-existence of memory RS and threshold RS behaviors. By properly regulating compliance current (Icc), the specified memory and threshold RS behaviors were observed: the memory RS behavior occurred with an Icc of 5 mA, the threshold RS behavior occurred with an Icc of 10 mA, and integrated one selector-one-RRAM (resistive random access memory) (1S1R) RS behavior occurred with an Icc of 50 mA. Moreover, individual RS behavior showed good performance, e.g., good stability of memory RS, good repeatability and concentrated voltage distribution of threshold RS. The memory RS behavior occurred mainly due to the formation and fracture of oxygen vacancy conductive filaments (CFs). Meanwhile, mediated by local Joule heating, thermally induced conductivity change was responsible for the threshold RS behavior. Under an Icc of 50 mA, the oxygen vacancy CFs and a thermally induced conductivity change triggered the 1S1R RS behavior, which significantly suppressed the leakage current in RRAM 3D integrated structures. This work provides an efficient and convenient method for modulating and obtaining the desired RS behavior and better understanding the conversion mechanism between them.

Extraction, chemical, and dual-functional memory and threshold resistive switching characteristics of Elaeodendron buchananii extract

This work presents a study on the electrical properties of plant materials, which is a fascinating area of research. These materials show promising potential in mitigating the exponential increase in electronic waste by enabling the development of eco-friendly electronic devices that can biodegrade. This research article showcases findings on the extraction, chemical analysis, and dual-functional memory and threshold resistive switching of extracts from the Elaeodendron buchananii plant. We report threshold switching with impressive ON/OFF ratio of >103, a retention time of ≥103, and endurance of 20 cycles, for the sandwich type device consisting of Elaeodendron buchananii plant extract-based film positioned between silver and indium-doped tin oxide electrodes. After modifying the experimental parameters, specifically by reducing the voltage scan increments to 1mV and increasing the compliance current to 150μA, transition from threshold switching to bipolar memory mode was detected. This particular memory mode exhibited an ON/OFF ratio of 10 and demonstrated very low switching voltages of −0.37V and +0.22V, although for only a limited number of write/erase cycles. The switching mechanism for both the threshold and memory mode can be attributed to the formation of conductive filaments caused by the migration of oxygen vacancies.

Phase transition induced threshold resistive switching in two-dimensional VTe2 nanosheets for Boolean logic operations

Vanadium chalcogenides have been extensively studied owing to the diverse crystallographic structures with various stoichiometric ratios. The metal-to-insulator transition (MIT) widely reported in vanadium chalcogenides is a rapid reversible phase transition that requires small energy, demonstrating potential applications in memory devices. In this work, two-dimensional (2D) vanadium telluride (VTe2) nanosheets are prepared by the chemical vapor deposition method. The synthesized VTe2 nanosheets exhibit volatile threshold switching (TS) behaviors due to the MIT phase transition, which can be further confirmed by the temperature dependent TS behaviors. The TS memristor demonstrates good stability and high reliability with up to 1000 continuous and repeatable writing/erasing operations. Furthermore, based on the TS behaviors, the fabricated memristor can be utilized to implement basic Boolean logic operations of “OR,” “AND,” and “NOT.” This study not only demonstrates the TS behaviors in the 2D VTe2 nanosheets owing to the MIT phase transition but also shows the potential applications of the TS devices in Boolean logic operations.

Self‐Assembly of Janus Graphene Oxide via Chemical Breakdown for Scalable High‐Performance Memristors

AbstractJanus 2D materials have drawn substantial attention recently owing to its extraordinary interface properties and promising applications in optoelectronic devices. However, the scalable fabrication of high‐quality Janus 2D materials is still one of the main obstacles to hinder its implementation in the industry. Herein, a new method (called “chemical breakdown”) is developed to obtain large‐area uniform Janus graphene oxide (J‐GO) films with high‐quality. Moreover, the first application of J‐GO in the field of memristive devices is presented for neuromorphic computing. In particular, crossbar arrays of Ag/J‐GO/Au memristive devices that exhibit threshold resistive switching (RS) with enhanced performance are fabricated, e.g., low leakage current (≈10−12 A), low operation voltage (≈0.3 V), high endurance (>12,000 cycles), and electro‐synaptic plasticity. This work provides a novel strategy to obtain large‐area, continuous and uniform Janus 2D films, and proposes a new application for Janus 2D materials in a hot topic (i.e., neuromorphic computing) within the field of solid‐state microelectronics.

Fully Optical in Operando Investigation of Ambient Condition Electrical Switching in MoS2 Nanodevices.

MoS2 nanoswitches have shown superb ultralow switching energies without excessive leakage currents. However, the debate about the origin and volatility of electrical switching is unresolved due to the lack of adequate nanoimaging of devices in operando. Here, three optical techniques are combined to perform the first noninvasive in situ characterization of nanosized MoS2 devices. This study reveals volatile threshold resistive switching due to the intercalation of metallic atoms from electrodes directly between Mo and S atoms, without the assistance of sulfur vacancies. A "semi-memristive" effect driven by an organic adlayer adjacent to MoS2 is observed, which suggests that nonvolatility can be achieved by careful interface engineering. These findings provide a crucial understanding of nanoprocess in vertically biased MoS2 nanosheets, which opens new routes to conscious engineering and optimization of 2D electronics.

Coexistence of memory and threshold resistive switching identified by combinatorial screening in niobium-tantalum system

Memristive devices exhibiting improved performance and memory characteristics are revealed by using a combinatorial screening approach. An Nb-Ta thin film library, with a total compositional spread ranging between 13 and 80 at.% Ta, is co-sputtered as the bottom electrode, while their anodic oxides served as active layers. Such metal–insulator-metal (MIM) specimens under investigation are finalized with patterned Pt top electrodes. Memristors based on mixed Nb2O5-Ta2O5 have been grouped according to their common switching characteristics in four different compositional zones. Reversible switching between threshold and non-volatile mode was observed for devices grown on Nb-39 at.% Ta alloy. The switching mode was dictated by applying different current compliances. Moreover, devices based on Nb-36 at.% Ta switch at minimum seven distinct resistive levels. Apart from the electrical measurements, the structure of samples and components distribution in cross-section geometry is studied via TEM techniques before and after electrical treatment. Electrolyte incorporation and the exact composition of the identified high-performance memristors (resulting from the combinatorial screening) are analyzed by HAXPES. The memristive devices based on the two singled-out Nb-Ta alloys show enhanced memory and electrical characteristics, thus being excellent candidates for neuromorphic applications.

Temperature of Conductive Nanofilaments in Hexagonal Boron Nitride Based Memristors Showing Threshold Resistive Switching (Adv. Electron. Mater. 8/2022)

Conductive Nanofilaments Ag/h-BN/Ag memristors exhibit stable threshold resistive switching because the temperature of the device during operation (at currents ≈1 μA) is very low (i.e. ≈310 K), due to the high in-plane thermal conductivity of h-BN and its low thickness. Only when the device is operated at higher currents (≈200 μA) the temperatures at the h-BN increase remarkably (>500 K), which produces a stable non-volatile conductive nanofilament. More details can be found in article number 2100580 by Mario Lanza, Felix Palumbo, and co-workers.

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.

Tunable Volatile to Non‐Volatile Resistive Switching in PbZrO3 Antiferroelectric Thin Film for Neuromorphic Computing

AbstractA direct coupling of antiferroelectric (AFE) and resistive switching (RS) is realized for the first time in an oxide heterostructures (non‐tunneling mechanisms). This allows the resistance of the heterostructure to switch between volatile and non‐volatile RS behavior, which indicates a threshold RS and broadly increases its practical applicability. The stacks of Pt/PbZrO3 (PZO)/LaNiO3/SrTiO3 (STO) is fabricated by laser pulse deposition. It exhibits a tunable RS behavior from volatile to nonvolatile through adjusting voltage amplitude. Moreover, a high ON/OFF ratio, good retention, and endurance characteristics are achieved. Furthermore, synaptic behaviors related to neural learning functions in PZO film is explored, that is, long‐term potential/depression, spike timing dependent plasticity, and paired pulse facilitation. This work provides a way to engineer AFE and RS pertinent functionality for the low‐energy‐consumption, non‐volatile neural computing.

Highly transparent flexible artificial nociceptor based on forming-free ITO memristor

Designing a flexible transparent electronic device with biological functions is of great interest for the future wearable integrated artificial intelligence equipment. Nociceptor is a vitally important receptor of sensory neuron, which is responsible for providing a warning signal by recognizing noxious stimuli to reduce potential physical injury. Here, a flexible transparent artificial nociceptor device is demonstrated to simulate the biological nociceptor functions based on the indium tin oxide (ITO) memristor, which exhibits forming-free and reproducible threshold resistive switching behaviors. This structurally simple memristor can imitate the key features of biological nociceptor, including “threshold,” “relaxation,” and “no adaptation” behaviors and sensitization phenomena of hyperalgesia and allodynia upon external stimuli. Finally, an alarm system is built to demonstrate the simplicity and feasibility of this artificial nociceptor for future neuromorphic systems. These results indicate a potential application of the ITO memristor in the future flexible invisible neuromorphic cognitive platform.

Self-rectifying threshold resistive switching based non-volatile memory of CBD/CBD grown vertical n-ZnO nanowire/p-Si heterojunction diodes

Vertically oriented ZnO nanowires are grown on p-Si substrate by employing two-step sequential chemical bath deposition technique. The ZnO nanowire exhibits n-type doping due to the presence of oxygen vacancies. The electrical characterizations of n-ZnO NWs/p-Si heterojunction diodes exhibit a self-rectifying, threshold resistive switching behavior. Such switching behavior is explained by oxygen vacancy assisted conducting filament formation mechanism. The relevant charge transport is governed by TC-SCLC and multistep recombination-tunneling processes through the interface traps. Threshold-voltage for resistive switching is observed to be increasing with increasing bias sweep rate. The device shows superior memory endurance for forward and reverse voltage sweep of 50 cycles in fast sweep mode. The ratio of HRS to LRS resistances shows one order of difference. The retention time of such resistive switching memory is recorded to be 4000 seconds, suggesting its non-volatile functionality. Thus, the n-ZnO NWs/p-Si heterojunction can be employed for fabricating promising non-volatile memory devices with excellent endurance and retentions. Copyright © 2018 VBRI Press.

Compliance Current-dependent Dual-functional Unipolar and Threshold Resistive Switching in Silver Nanowires-egg Albumen Composites-based Device

The continued exploration of novel synthetic memristive materials with multifunctional properties is critical for future synapse-emulating circuits and electronic devices in the field of next-generation neuromorphic computing applications. In this work, the silver nanowires (AgNWs)-Egg albumen composites have been integrated as a resistive switching layer in the Ag/AgNWs-Egg albumen/Ag planar structure and exhibits both unipolar (memory) switching and threshold switching functions. The device in unipolar switching regime demonstrates an ON/OFF ratio above 105, a low resistance state of about 1.2 KΩ and a high resistance state of about 120 MΩ. Finally, a mechanism in combination with the conductive filament theory and a tunnelling conduction mechanism is proposed to explain the resistive switching behavior. The devices are prepared by simple and low-cost techniques, which make such devices appealing for future electronic applications.

Temperature of Conductive Nanofilaments in Hexagonal Boron Nitride Based Memristors Showing Threshold Resistive Switching

AbstractTwo‐terminal metal/insulator/metal (MIM) memristors exhibiting threshold resistive switching (RS) can develop advanced key tasks in solid‐state nano/micro‐electronic circuits, such as selectors and integrate‐and‐fire electronic neurons. MIM‐like memristors using multilayer hexagonal boron nitride (h‐BN) as dielectric are especially interesting because they have shown threshold RS with ultra‐low energy consumption per state transition down to the zeptojoule regime. However, the factors enabling stable threshold RS at such low operation energies are still not fully understood. Here it is shown that the threshold RS in 150 nm × 150 nm Au/Ag/h‐BN/Au memristors is especially stable because the temperature in the h‐BN stack during operation (i.e., at low currents ≈1 μA) is very low (i.e., ≈310 K), due to the high in‐plane thermal conductivity of h‐BN and its low thickness. Only when the device is operated at higher currents (i.e., ≈200 μA) the temperatures at the h‐BN increase remarkably (i.e., >500 K), which produce a stable non‐volatile conductive nanofilament (CNF). This work can bring new insights to understand the performance of 2D materials based RS devices, and help to develop the integration of 2D materials in high‐density nanoelectronics.

Coexistence of nonvolatile unipolar and volatile threshold resistive switching in the Pt/LaMnO3/Pt heterostructures

Coexistence of nonvolatile unipolar and volatile threshold resistive switching is observed in the Pt/LaMnO3 (LMO)/Pt heterostructures. The nonvolatile unipolar memory is achieved by applying a negative bias, while the volatile threshold resistive switching is obtained under a positive bias. Additionally, the pristine low resistance state (LRS) could be switched to high resistance state (HRS) by the positive voltage sweeping, which is attributed to the conduction mechanism of Schottky emission. Subsequently, the insulator-to-metal transition in the LMO film due to formation of ferromagnetic metallic phase domain contributes to the volatile threshold resistive switching. However, the nonvolatile unipolar switching under the negative bias is ascribed to the formation/rupture of oxygen-vacancy conducting filaments. The simultaneously controllable transition between nonvolatile and volatile resistance switching by the polarity of the applied voltage exhibits great significance in the applications of in-memory computing technology.

Coexistence of memory and threshold switching behaviors in natural milk-based organic memristor

Natural biomaterials have attracted great interest for the fabrication of biocompatible memristors. Here, dense and smooth milk films were deposited on the Pt/SiO2/Si substrate by spin-coating method and resistive switching (RS) devices based milk films with the configuration of Ag/milk/Pt/SiO2/Si are fabricated for the first time. Furthermore, memory RS (MRS) and threshold RS (TRS) effects coexist in the devices, which can be controlled by appropriately setting the compliance current (I cc). The current conduction mechanisms of the devices with MRS and TRS effects are controlled by typical trap-controlled space charge limited current (SCLC) conduction and filamentary conduction mechanism. The good RS performances of the milk-based devices make them promising for sustainable bioelectronics and novel logic device applications.

Memristive Behavior of Mixed Oxide Nanocrystal Assemblies

Recent advances in memristive nanocrystal assemblies leverage controllable colloidal chemistry to induce a broad range of defect-mediated electrochemical reactions, switching phenomena, and modulate active parameters. The sample geometry of virtually all resistive switching studies involves thin film layers comprising monomodal diameter nanocrystals. Here we explore the evolution of bipolar and threshold resistive switching across highly ordered, solution-processed nanoribbon assemblies and mixtures comprising BaZrO3 (BZO) and SrZrO3 (SZO) nanocrystals. The effects of nanocrystal size, packing density, and A-site substitution on operating voltage (VSET and VTH) and switching mechanism were studied through a systematic comparison of nanoribbon heterogeneity (i.e., BZO-BZO vs BZO-SZO) and monomodal vs bimodal size distributions (i.e., small-small and small-large). Analysis of the current-voltage response confirms that tip-induced, trap-mediated space-charge-limited current and trap-assisted tunneling processes drive the low- and high-resistance states, respectively. Our results demonstrate that both smaller nanocrystals and heavier alkaline earth substitution decrease the onset voltage and improve stability and state retention of monomodal assemblies and bimodal nanocrystal mixtures, thus providing a base correlation that informs fabrication of solution-processed, memristive nanocrystal assemblies.

Planar and Transparent Memristive Devices Based on Titanium Oxide Coated Silver Nanowire Networks with Tunable Switching Voltage.

Threshold switching devices are fundamental active elements in more than Moore approaches, integrating the new generation of non-volatile memory devices. Here, the authors report an in-plane threshold resistive switching device with an on/off ratio above 106 , a low resistance state of 10 to 100 kΩ and a high resistance state of 10 to 100 GΩ. Ourdevices are based on nanocomposites of silver nanowire networks and titanium oxide, where volatile unipolar threshold switching takes place across the gap left by partially spheroidized nanowires. Device reversibility depends on the titanium oxide thickness, while nanowire network density determines the threshold voltage, which can reach as low as 0.16V. The switching mechanism is explained through percolation between metal-semiconductor islands, in a combined tunneling conduction mechanism, followed by a Schottky emission generated via Joule heating. The devices are prepared by low-cost, atmospheric pressure, and scalable techniques, enabling their application in printable, flexible, and transparent electronics.

Partially Oxidized MXene Ti3C2Tx Sheets for Memristor having Synapse and Threshold Resistive Switching Characteristics

AbstractTransition metal carbides, called MXenes, can be used for MXene‐based unique electronic devices such as new types of batteries, energy storage devices, and supercapacitors, where MXene is used as an electrode. The unique surface properties of MXene and 2D structure can be further applied to the new electronic devices. In this paper, the unique insulating properties of partially oxidized MXene (Ti3C2Tx) sheets are utilized for memory storage and electronic synapse applications. The device exhibits threshold resistive switching characteristics based on Ag+ migration dynamics. It is found that this Ag+ cation migration is similar to Ca2+ ion dynamics of a biological synapse, and thus, biological synapse functions such as intrusion/extrusion of Ag+ cation, paired‐pulse facilitation (PPF), post‐tetanic potentiation (PTP), short‐term potentiation (STP), and transition of STP to long‐term potentiation (LTP) are well‐emulated. It is believed that this device development can be potentially used in the next‐generation hardware‐based artificial intelligence systems.

Optically excited threshold switching synapse characteristics on nitrogen-doped graphene oxide quantum dots (N-GOQDs)

Carbon-based organic material such as nitrogen-doped graphene oxide quantum dots (N-GOQDs) is a new-class material with unique biocompatible, high chemical inertness, and elevated photoluminescence properties. Two-terminal diffusive memristors can faithfully replicate biological synapse function via mutual similarities of in-/out-diffusion of Ag+ ions with biological Ca2+ migration dynamics for neural network applications. Inspired by hetero-plasticity phenomenon, in which Ca2+ dynamics can also be tuned by the 3rd counterpart – neuromodulatory axon, in this study, using an ultra-violet light source, we develop N-GOQDs based diffusive memristor that performs light-modulated synaptic behaviors. Specifically, photo-sensitive N-GOQDs ionic conductor shows n-π∗ electron transitions under UV excitation; yet, nitrogen-doping further facilitates the electron transitions, giving out additional conductance induced by light. Further, we demonstrate endurable threshold resistive switching (TS) behavior based on Ag+ ions migration and its variety of facilitations via assisted UV illumination. The enhancement of post-synaptic current under assisted UV light, as well as the light stimulated transition from short-to long-term memory potentiation have been achieved. These findings are believed to be a step forward for the realization of higher bandwidth synapse modulation as future hardware-based neural network applications.

Non-Polar Selector Operation Brought about By Coo/ITO Double Layer Structures

As memory devices get more and more highly integrated, the development of selectors that enables 3D crossbar structures is required, to suppress the current leakage called ’sneak path current’ that flows through unselected cells and half-selected cells. In this paper, we investigated a p-type semiconductor of CoO deposited on tin-doped indium oxide (ITO). We confirmed that non-polar, volatile, and very fast threshold resistance switching with a small dispersion of threshold voltage.