Nonvolatile Resistive Switching Behavior Research Articles

Resistive switching of self-assembly stacked h-BN polycrystal film

Two-dimensional materials resistive random-access memories (RRAMs) are known to exhibit excellent nonvolatile resistive switching (NVRS) performance. However, most two-dimensional materials are produced as monocrystal films with little attention paid to their stacked, discontinuous, and loose polycrystal states, which may allow for more facile atomic diffusion. Here, we propose a liquid-phase self-assembly (LPSA) method to fabricate stacked hexagonal boron nitride (h-BN) polycrystal film (SHPF) and demonstrate its NVRS behavior. Three device architectures with different electrodes are studied, all of which exhibit resistive switching behaviors. The Al/h-BN/Pt device shows 120 current-voltage (I-V) sweeps without degradation, and the Al/h-BN/ITO device exhibits an on/off ratio of ∼10 4 . The proposed LPSA method can serve as a facile and low-cost way to fabricate memory materials on arbitrary substrates. Moreover, stacked, discontinuous, and loose polycrystal film can facilitate the study of NVRS, which opens up an additional avenue for many potential functional applications. • Stacked h-BN polycrystal film (SHPF)-based RRAM is studied • Record nonvolatile resistance switching (NVRS) is observed in SHPF • Reliable NVRS with 120 cycles of endurance and on/off ratio as high as ∼10 4 • SHPF is realized by facile and low-cost self-assembly with no limit from substrate Sun et al. develop a method for fabricating large-area 2D-material film on arbitrary substrate and study the resistive switching of stacked polycrystal h-BN film. The devices show excellent nonvolatile-resistive-switching performance, and the study provides an alternative approach for 2D-material fabrication and applications.

A low-power memristor based on 2H–MoTe2 nanosheets with synaptic plasticity and arithmetic functions

Bionic artificial synapses based on 2D transition metal dichalcogenides are comparable to biological synapses due to the unique properties, which are important for building brain-like computing to break the energy and data throughput limit of the von Neumann architecture. In this work, a two-terminal memristor with vertical structure was fabricated by using 2H–MoTe2 nanosheet dispersion. The fabricated memristor based on the Cu/MoTe2/Si structure not only exhibits the stable bipolar nonvolatile resistive switching behavior but also implements the centralized distribution of threshold voltage, and the SET/RESET power can be as low as 0.86 μW/93 nW. Impressively, classical synaptic functions including long-term potentiation/long-term depression, excitatory postsynaptic currents, spike-timing-dependent plasticity, and paired-pulse facilitation were mimicked, which attribute to the formation and rupturing of Cu conductive filaments. Interestingly, the simple arithmetic functions can be operated. Therefore, this work provides a new solution for the development of synaptic devices and neural computing research in the future.

Electron irradiation-induced defects for reliability improvement in monolayer MoS2-based conductive-point memory devices

Monolayer molybdenum disulfide has been previously discovered to exhibit non-volatile resistive switching behavior in a vertical metal-insulator-metal structure, featuring ultra-thin sub-nanometer active layer thickness. However, the reliability of these nascent 2D-based memory devices was not previously investigated for practical applications. Here, we employ an electron irradiation treatment on monolayer MoS2 film to modify the defect properties. Raman, photoluminescence, and X-ray photoelectron spectroscopy measurements have been performed to confirm the increasing amount of sulfur vacancies introduced by the e-beam irradiation process. The statistical electrical studies reveal the reliability can be improved by up to 1.5× for yield and 11× for average DC cycling endurance in the devices with a moderate radiation dose compared to unirradiated devices. Based on our previously proposed virtual conductive-point model with the metal ion substitution into sulfur vacancy, Monte Carlo simulations have been performed to illustrate the irradiation effect on device reliability, elucidating a clustering failure mechanism. This work provides an approach by electron irradiation to enhance the reliability of 2D memory devices and inspires further research in defect engineering to precisely control the switching properties for a wide range of applications from memory computing to radio-frequency switches.

Volatile and Nonvolatile Memristive Devices for Neuromorphic Computing

AbstractIon migration as well as electron transfer and coupling in resistive switching materials endow memristors with a physically tunable conductance to resemble synapses, neurons, and their networks. Four different types of volatile memristors and another four types of nonvolatile memristors are systemically surveyed in terms of the switching mechanisms and electrical properties that are the basis of different computing applications. The volatile memristor features spontaneous conductance decay after the cease of electrical/optical stimulations, which are closely related to the surface atom diffusion, metal–insulator–transition (including charge–density–wave), thermal spontaneous emission, and charge polarization. Such unique dynamic state evolution at the edge of chaos has enabled them to emulate certain synaptic and neural dynamics, leading to various applications ranging from spiking neural networks to combinatorial optimizations. Nonvolatile resistive switching behavior originated from the electron spins, ferroelectric polarization, crystalline‐amorphous transitions or interplay between ions and electrons enables the memristor array to implement the vector–matrix multiplication, which is the key convolutional operation in artificial neural networks. The progress, challenges, and opportunities for both volatile and nonvolatile memristor in the level of materials, integration technology, algorithm, and system are highlighted in this review.

Transition from synaptic simulation to nonvolatile resistive switching behavior based on an Ag/Ag:ZnO/Pt memristor.

The advent of memristors and the continuing research and development in the field of brain-inspired computing could allow realization of a veritable "thinking machine". In this study, ZnO-based memristors were fabricated using a radio frequency magnetron sputtering method. The ZnO oxide layer was prepared by incorporating silver nanocrystals (NCs). Several synaptic functions, i.e. nonlinear transmission characteristics, short-term potentiation, long-term potentiation/depression, and pair-pulse facilitation, were imitated in the memristor successfully. Furthermore, the transition from synaptic behaviors to bipolar resistive switching behaviors of the device was also observed under repeated stimulus. It is speculated that the switching mechanism is due to the formation and rupture of the conductive Ag filaments and the corresponding electrochemical metallization. The experimental results demonstrate that the Ag/Ag:ZnO/Pt memristor with resistive switching and several synaptic behaviors has a potential application in neuromorphic computing and data storage systems.

3D-structured mesoporous silica memristors for neuromorphic switching and reservoir computing.

Memristors are emerging as promising candidates for practical application in reservoir computing systems that are capable of temporal information processing. Here, we experimentally implement a physical reservoir computing system using resistive memristors based on three-dimensional (3D)-structured mesoporous silica (mSiO2) thin films fabricated by a low cost, fast and vacuum-free sol-gel technique. The in situ learning capability and a classification accuracy of 100% on a standard machine learning dataset are experimentally demonstrated. The volatile (temporal) resistive switching in diffusive memristors arises from the formation and subsequent spontaneous rupture of conductive filaments via diffusion of Ag species within the 3D-structured nanopores of the mSiO2 thin film. Besides volatile switching, the devices also exhibit a bipolar non-volatile resistive switching behavior when the devices are operated at a higher compliance current level. The implementation of mSiO2 thin films opens the route to fabricate a simple and low cost dynamic memristor with a temporal information process functionality, which is essential for neuromorphic computing applications.

ReSe2-Based RRAM and Circuit-Level Model for Neuromorphic Computing

Resistive random-access memory (RRAM) devices have drawn increasing interest for the simplicity of its structure, low power consumption and applicability to neuromorphic computing. By combining analog computing and data storage at the device level, neuromorphic computing system has the potential to meet the demand of computing power in applications such as artificial intelligence (AI), machine learning (ML) and Internet of Things (IoT). Monolayer rhenium diselenide (ReSe2), as a two-dimensional (2D) material, has been reported to exhibit non-volatile resistive switching (NVRS) behavior in RRAM devices with sub-nanometer active layer thickness. In this paper, we demonstrate stable multiple-step RESET in ReSe2 RRAM devices by applying different levels of DC electrical bias. Pulse measurement has been conducted to study the neuromorphic characteristics. Under different height of stimuli, the ReSe2 RRAM devices have been found to switch to different resistance states, which shows the potentiation of synaptic applications. Long-term potentiation (LTP) and depression (LTD) have been demonstrated with the gradual resistance switching behaviors observed in long-term plasticity programming. A Verilog-A model is proposed based on the multiple-step resistive switching behavior. By implementing the LTP/LTD parameters, an artificial neural network (ANN) is constructed for the demonstration of handwriting classification using Modified National Institute of Standards and Technology (MNIST) dataset.

Enhanced Memristive Performance of Double Perovskite Cs2 AgBiBr6-x Clx Devices by Chloride Doping.

Mixed halide perovskites are promising memristive materials because of their excellent electronic-ionic properties. In this work, lead-free Cs2 AgBiBr6-x Clx (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite films were fabricated using a one-step solution spin-coating method in air. Moreover, the ITO/Cs2 AgBiBr6-x Clx /Al sandwich-like devices are fabricated to investigate the memristive behaviors. The present memristors exhibit nonvolatile and bipolar resistive switching behaviors without electroforming process. Interestingly, as the chloride content increases, the ON/OFF ratio of the device increases from 103 to 104 , the average SET voltage and the RESET voltage decrease from -0.40 V to -0.21 V and from 1.55 V to 1.34 V, respectively. In addition, resistance states of devices can be maintained after 100 switching cycles and 104 s of reading. This study provides new possibility for the development of low-power and environmentally friendly memristors.

Nonvolatile resistive switching memory based on monosaccharide fructose film

In this paper, we report resistive random access memory (RRAM) based on a monosaccharide—fructose for nonvolatile memory in biocompatible and “green” electronics. Fructose thin film acts as the resistive switching layer with Al and Ag top electrodes for comparison. Both devices demonstrated highly reproducible nonvolatile bipolar resistive switching behaviors with a large on/off ratio of ∼106 for the Al electrode and ∼105 for the Ag electrode. The forming voltage, set voltage, and memory window are also larger for the Al electrode than the Ag electrode, but the reset voltages are comparable. Dominant conduction mechanisms of fructose films were proposed. At a high resistance state, both electrodes reveal space charge limited conduction, while at a low resistance state, the governing mechanism is Ohm's law, and in addition, the Ag electrode also shows trap-fill limited conduction when approaching the reset voltage. This observation has yet to be reported in RRAM based on natural bio-organic materials.

Observation of nonvolatile resistive switching behaviors in 2D layered InSe nanosheets through controllable oxidation

Scientists have been seeking for suitable materials with nonvolatile resistive switching (RS) performance for memristive applications. Recently, nonvolatile RS behaviors have been achieved in an increasing number of two-dimensional (2D) materials. However, 2D InSe layers have not been reported to demonstrate such nonvolatile RS behaviors. Herein, we experimentally observe nonvolatile bipolar RS behaviors in 2D InSe nanosheets through controllable oxidation. In our experiments, the exfoliated InSe nanosheets annealed at the temperature of 350 °C for 2 h show typical nonvolatile bipolar RS performance with a low SET voltage of ∼0.3 V and a high ON/OFF ratio of 4.5 × 103 at the read voltage of 0.1 V. Raman and x-ray photoelectron spectroscopy characterizations confirm the partial oxidation in InSe nanosheets after annealing. The observed nonvolatile RS behaviors are owing to the formation of In2O3 and the increased insulating characteristic in the annealed InSe nanosheets. Furthermore, the fabricated memristor exhibits good retention property and endurance performance. Such annealed InSe nanosheets not only demonstrate decent RS performance but also enrich the family of 2D materials to fabricate memristors for applications in next-generation nonvolatile memory.

Memristor Based on Inorganic and Organic Two-Dimensional Materials: Mechanisms, Performance, and Synaptic Applications.

A memristor is a two-terminal device with nonvolatile resistive switching (RS) behaviors. Recently, memristors have been highly desirable for both fundamental research and technological applications because of their great potential in the development of high-density memory technology and neuromorphic computing. Benefiting from the unique two-dimensional (2D) layered structure and outstanding properties, 2D materials have proven to be good candidates for use in gate-tunable, highly reliable, heterojunction-compatible, and low-power memristive devices. More intriguing, stable and reliable nonvolatile RS behaviors can be achieved in multi- and even monolayer 2D materials, which seems unlikely to be achieved in traditional oxides with thicknesses less than a few nanometers because of the leakage currents. Moreover, such two-terminal devices show a series of synaptic functionalities, suggesting applications in simulating a biological synapse in the neural network. In this review article, we summarize the recent progress in memristors based on inorganic and organic 2D materials, from the material synthesis, device structure and fabrication, and physical mechanism to some versatile memristors based on diverse 2D materials with good RS properties and memristor-based synaptic applications. The development prospects and challenges at the current stage are then highlighted, which is expected to inspire further advancements and new insights into the fields of information storage and neuromorphic computing.

Influence of adsorption small molecules atrazine on nonvolatile resistive switching behavior in Co–Al layered double hydroxide films

Co–Al-layered double hydroxides (LDHs) thin films were prepared by drop-casting process on ITO-coated glass substrates. And then the small molecule atrazine was adsorbed on the Co–Al LDHs film by impregnation method. Current–voltage characteristics revealed nonvolatile resistive switching in Co–Al LDHs adsorbed atrazine films. The Influence of adsorption small molecules atrazine on nonvolatile resistive switching behavior in Co–Al LDHs film has been investigated. By varying the atrazine adsorbed content in Co–Al LDHs thin films, the nonvolatile resistive switching behavior of device could be adjusted in a controlled way. Entirely different nonvolatile resistive switching characteristic, such as write-once read-many-times memory effect and rewritable memory effect are discriminable by the current–voltage curves.

A synaptic memristor based on two-dimensional layered WSe2 nanosheets with short- and long-term plasticity

Neural synapses with diverse synaptic functions of short- and long-term plasticity are highly desired for developing complex neuromorphic systems. A memristor with its two terminals serving as pre- and post-neurons, respectively, can emulate two neuronal-based synaptic functions. In this work, multilayer two-dimensional (2D) layered WSe2 nanosheets are synthesized by a salt-assisted chemical vapor deposition (CVD) method. Two-terminal memristors with a planar structure are fabricated based on the CVD-grown triangular WSe2 nanosheets. The fabricated devices exhibit typical bipolar nonvolatile resistive switching behaviors with a high current ON/OFF ratio of up to 6 × 103 and good retention and endurance properties, suggesting good stability and reliability of the WSe2-based memristors. Furthermore, the developed memristors demonstrate synaptic functions of short- and long-term plasticity (STP and LTP), as well as a transition from STP to LTP by applying consecutive pulse voltages. Moreover, the WSe2-based memristors exhibits biological synaptic functions of long-term potentiation and depression, and paired-pulse facilitation. Thus, our 2D WSe2 nanosheet based memristors not only exhibit stable and reliable nonvolatile resistive switching behaviors, but also show potential applications in mimicking biological synapses.

Nonvolatile Resistive Switching of Mn3O4 Thin Films for Flexible Electronics Applications

Introduction: We report here our success in developing a flexible RRAM stack structure by employing a low-cost method. Bare conductive commercial electric paint is used as anode against Stainless Steel (SS) foil deposited with Mn3O4 thin films forming a BCEP/Mn3O4/SS thin film stack to understand the intrinsic non-volatile resistive switching behavior of Mn3O4. Experimental: Thin film Mn3O4 is deposited on a SS (304) foil by means of potential sweep voltammetry by maintaining typical conditions. Interestingly, the pristine device is subjected to an electroforming process which exhibited a digital type bipolar resistive switching characteristics. The study of the conduction mechanism revealed that the resistive switching arises due to local effect occurring in the bulk of Mn3O4, which corresponds to the growth and annihilation of oxygen vacancy nanofilaments, and this is responsible for the change in resistance state of the RRAM between Low Resistance State (LRS) and High Resistance State (HRS) respectively. Results: In order to affirm the reliability and reproducibility of RRAM structure, the memory retention is monitored over 103 s and subsequently, the endurance test is also carried out ensuring the reproducibility over 100 cycles. Conclusion: Owing to the flexible nature of BCEP/Mn3O4/SS Foil RRAM stack structure, it is perceived to be a prime candidate for future non-volatile memory and flexible electronics applications.

Programmable electronic synapse and nonvolatile resistive switches using MoS2 quantum dots

Brain-inspired computation that mimics the coordinated functioning of neural networks through multitudes of synaptic connections is deemed to be the future of computation to overcome the classical von Neumann bottleneck. The future artificial intelligence circuits require scalable electronic synapse (e-synapses) with very high bit densities and operational speeds. In this respect, nanostructures of two-dimensional materials serve the purpose and offer the scalability of the devices in lateral and vertical dimensions. In this work, we report the nonvolatile bipolar resistive switching and neuromorphic behavior of molybdenum disulfide (MoS2) quantum dots (QD) synthesized using liquid-phase exfoliation method. The ReRAM devices exhibit good resistive switching with an On–Off ratio of 104, with excellent endurance and data retention at a smaller read voltage as compared to the existing MoS2 based memory devices. Besides, we have demonstrated the e-synapse based on MoS2 QD. Similar to our biological synapse, Paired Pulse Facilitation / Depression of short-term memory has been observed in these MoS2 QD based e-synapse devices. This work suggests that MoS2 QD has potential applications in ultra-high-density storage as well as artificial intelligence circuitry in a cost-effective way.

NiO-based memristor with three resistive switching modes

In this research, solution-processed NiO-based memristors have been demonstrated with three resistive switching modes, including analog resistive switching, volatile threshold resistive switching and nonvolatile digital resistive switching, where the specific behavior is determined by the applied bias voltage and compliance current. The analog resistive switching is achieved via local oxygen ion migration at the NiO/Ag interface under low voltage stress. Based on this resistive switching mode, several synaptic functions are mimicked. When the device is stressed using a high voltage and a low compliance current, the device behavior changes to volatile threshold resistive switching. This behavior allows spiking neuron functions to be simulated. Furthermore, under application of a high compliance current, the device behavior converts to nonvolatile digital resistive switching. Ag filament formation and rupture processes are considered to be the mechanism behind the volatile threshold and nonvolatile resistive switching behavior. This multifunctional NiO-based memristor will provide a basis for fabrication of memory devices, analog circuits and artificial neural networks.

Interfacial layer assisted, forming free, and reliable bipolar resistive switching in solution processed BiFeO3 thin films

BiFeO3 based resistive random access memory (RRAM) devices are fabricated using a low-cost solution process to study the effect of an Al top electrode on switching behavior and reliability. Fabricated devices demonstrated bipolar switching characteristics with a moderate Ion/Ioff ratio, set and reset voltages of ∼−1.3 V and ∼0.8 V, DC and AC endurance of more than 250 cycles and 7100 cycles, respectively, and a retention time of over 104 s, confirming the non-volatile resistive switching behavior. The ohmic and trap filled space charge limited conduction dominates the conduction mechanism in the devices at lower and higher voltages, respectively. Moreover, impedance spectroscopy measurements substantiate the presence of an AlOx layer at the Al/BiFeO3 interface resulting from the Al–O interaction at the junction, which is the possible rationale of reliable complementary switching in these RRAM devices. The switching mechanism is elucidated using the formation and rupture of the oxygen vacancy mediated filament, assisted by the participation of a thin AlOx layer at the Al/BFO interface. The role of the thin AlOx layer is explained by modeling of impedances.

Logic Gate Functions Built with Nonvolatile Resistive Switching and Thermoresponsive Memory Based on Biologic Proteins.

Logic gate functions built with nonvolatile resistive switching and thermoresponsive memory based on biologic proteins were investigated. The "NAND" and "NOR" functions of logic gates in soya protein devices have been built at room temperature by their nonvolatile ternary WORM resistive switching behaviors. Furthermore, heating the devices from room temperature to 358 K results in a switch from tristable state to bistable state WORM resistive switching behavior, indicating that the thermoresponsiveness can be efficiently memorized. The biologic transient nonvolatile memory device consisting of soya protein is illustrated. This device exhibits a long data retention time (104 s) and significant HRS/LRS ratio (∼105); the transient response of the current to voltage of an as-fabricated device is also explored. The soya protein based memory device on a gelatin film substrate is also assessed to validate the feasibility of degradation and biological compatibility for the implantable biological electronic device, that is, innoxious and avirulent to the human body. This can offer alternative avenues for exploring prospective bioelectronic devices.

Multipurpose conjugated block copolymers based on novel triphenylylamine derivatives and squaric acid for electrochromic and resistive memory devices

Here, we synthesized two kinds of novel conjugated block copolymers P1 and P2 by reacting squaric acid and three kinds of homemade diamine monomers. The polymers P1 and P2 can be dissolved in many normal organic solvents and form films by solution-cast method with high mechanical properties. In addition, when the 10% weight loss is selected as a reference point, the polymers P1 and P2 showed the thermal decomposition temperatures at around 309 and 312 °C, respectively. The polymer films exhibit high coloration efficiencies (CE) (262–282 cm2 C−1) and good cyclic stabilities. In addition, the ITO/polymer/Al sandwich memory devices exhibited non-volatile resistive switching behaviors with low write, erase voltages (more than −0.6 V and less than 3.1 V, respectively), good ON/OFF ratio (843 and 1435) and reliable cycling endurance (more than 30,000 cycles). These properties illustrate that the polymers could be considered as potential electrode materials for both electrochromic and resistive memory devices.

Organic resistive switching device based on cellulose-gelatine microcomposite fibers

The present work demonstrates the non-volatile resistive switching behavior of cellulose-gelatine microcomposite fibers (CGMFs). The CGMFs were synthesized using the electrospinning technique and used as a switching layer for a resistive memory device. The morphological study reveals that the switching layer was composed of good quality of microcomposite fibers and possesses cross-link like morphology. The functional groups present in the switching layer were confirmed by Fourier-transform infrared spectroscopy technique. The CGMFs based device shows the bipolar resistive switching effect and requires low SET (+ 1.33 V) and RESET (− 1.42 V) voltages for the operation. The charge-magnetic flux relation of the device was calculated and memristive device like properties were observed from the results. The charge driving capability of the device was found to be ~ 1.3 × 10−2 C, which is sufficient to get the good resistive switching property. The non-volatile resistive switching behavior of the CGMFs based device suggested that the device has good performance in terms of endurance (500 cycles) and retention (2000 s). The uniformity and reliability of the device were confirmed by statistical calculations (standard deviation and coefficient of variation). The conduction model fitting results suggested that the space charge limited current (SCLC) and Ohmic conduction mechanisms were responsible for device operation during the high resistance state (HRS) and low resistance state (LRS), respectively. A possible resistive switching mechanism is presented by considering the formation and rupture of Ag conductive filament under the influence of external voltage.