Tunable Resistive Switching Research Articles

Security enhancement of artificial neural network using physically transient form of heterogeneous memristors with tunable resistive switching behaviors

Security enhancement of artificial neural network using physically transient form of heterogeneous memristors with tunable resistive switching behaviors

Tunable Resistive Switching Behaviors and Mechanism of the W/ZnO/ITO Memory Cell.

A facile sol-gel spin coating method has been proposed for the synthesis of spin-coated ZnO nanofilms on ITO substrates. The as-prepared ZnO-nanofilm-based W/ZnO/ITO memory cell showed forming-free and tunable nonvolatile multilevel resistive switching behaviors with a high resistance ratio of about two orders of magnitude, which can be maintained for over 103 s and without evident deterioration. The tunable nonvolatile multilevel resistive switching phenomena were achieved by modulating the different set voltages of the W/ZnO/ITO memory cell. In addition, the tunable nonvolatile resistive switching behaviors of the ZnO-nanofilm-based W/ZnO/ITO memory cell can be interpreted by the partial formation and rupture of conductive nanofilaments modified by the oxygen vacancies. This work demonstrates that the ZnO-nanofilm-based W/ZnO/ITO memory cell may be a potential candidate for future high-density, nonvolatile, memory applications.

Tunable resistive switching in shales

Electrically induced resistive switching is a subject of increasing scientific interest because it is a candidate for universal non-volatile memory. We demonstrate resistive switching in a natural reservoir shale. The resistance of the rocks is repeatedly switched between the high-resistance state and low-resistance state, being controlled by the setting and measuring voltages as well as the duration of excitation. The shale can be continuously switched over 40 times under appropriate voltage pulses with a maximum on/off ratio higher than 20, as well as small energy consumption and a power density of less than 1 mW/mm2 at 40 V. This phenomenon has also been observed in tight sandstones and some other sedimentary rocks. In contrast to conventional resistive memory devices, rocks with tunable properties are promising for data storage applications because of their low cost and simplicity, as well as being easily and safely disposable. Rocks and minerals with tunable properties are promising for storage applications, which may provide the functional use of those materials.

Highly Reproducible Heterosynaptic Plasticity Enabled by MoS2/ZrO2-x Heterostructure Memtransistor.

Electrically tunable resistive switching of a polycrystalline MoS2-based memtransistor has attracted a great deal of attention as an essential synaptic component of neuromorphic circuitry because its switching characteristics from the field-induced migration of sulfur defects in the MoS2 grain boundaries can realize multilevel conductance tunability and heterosynaptic functionality. However, reproducible switching properties in the memtransistor are usually disturbed by the considerable difficulty in controlling the concentration and distribution of the intrinsically existing sulfur defects. Herein, we demonstrate reliable heterosynaptic characteristics using a memtransistor device with a MoS2/ZrO2-x heterostructure. Compared to the control device with the MoS2 semiconducting channel, the Schottky barrier height was more effectively modulated by the insertion of the insulating ZrO2-x layer below the MoS2, confirmed by an ultraviolet photoelectron spectroscopy analysis and the corresponding energy-band structures. The MoS2/ZrO2-x memtransistor accomplishes dual-terminal (drain and gate electrode) stimulated multilevel conductance owing to the tunable resistive switching behavior under varying gate voltages. Furthermore, the memtransistor exhibits long-term potentiation/depression endurance cycling over 7000 pulses and stable pulse cycling behavior by the pulse stimulus from different terminal regions. The promising candidate as an essential synaptic component of the MoS2/ZrO2-x memtransistors for neuromorphic systems results from the high recognition accuracy (∼92%) of the deep neural network simulation test, based on the training and inference of handwritten numbers (0-9). The simple memtransistor structure facilitates the implementation of complex neural circuitry.

Tunable Resistive Switching in 2D MXene Ti3C2 Nanosheets for Non-Volatile Memory and Neuromorphic Computing.

An artificial synapse is essential for neuromorphic computing which has been expected to overcome the bottleneck of the traditional von-Neumann system. Memristors can work as an artificial synapse owing to their tunable non-volatile resistance states which offer the capabilities of information storage, processing, and computing. In this work, memristors based on two-dimensional (2D) MXene Ti3C2 nanosheets sandwiched by Pt electrodes are investigated in terms of resistive switching (RS) characteristics, synaptic functions, and neuromorphic computing. Digital and analog RS behaviors are found to coexist depending on the magnitude of operation voltage. Digital RS behaviors with two resistance states possessing a large switching ratio exceeding 103 can be achieved under a high operation voltage. Analog RS behaviors with a series of resistance states exhibiting a gradual change can be observed at a relatively low operation voltage. Furthermore, artificial synapses can be implemented based on the memristors with the basic synaptic functions, such as long-term plasticity of long-term potentiation and depression and short-term plasticity of the paired-pulse facilitation and depression. Moreover, the "learning-forgetting" experience is successfully emulated based on the artificial synapses. Also, more importantly, the artificial synapses can construct an artificial neural network to implement image recognition. The coexistence of digital and analog RS behaviors in the 2D Ti3C2 nanosheets suggests the potential applications in non-volatile memory and neuromorphic computing, which is expected to facilitate simplifying the manufacturing complexity for complex neutral systems where analog and digital switching is essential for information storage and processing.

Tunable Switching Behavior of GO-Based Memristors Using Thermal Reduction.

This work reports on the fabrication of a novel planar reduced graphene oxide (rGO) memristor (MR) device. For the first time in the literature, the MR tunable resistive switching behavior is controlled by the GO reduction time at a constant temperature. The device is fabricated using standard microfabrication techniques on a flexible cyclic olefin copolymer substrate (COC). Thermal reduction of the GO layer at low temperatures (100 °C) avoids the drawbacks of chemical reduction methods such as toxicity and electrode metal damage during fabrication, while allowing for fine-tuning of the MR’s switching behavior. The device has analog switching characteristics, with a range of different resistance states. By taking advantage of the slow nature of GO thermal annealing, the switching properties of the rGO memristors can be precisely controlled by adjusting the reduction period. At short annealing times (i.e., T < 20 h), the devices switch from high to low resistance states, while at longer annealing times the switching behavior is reversed, with the device switching from low to high resistance states (LRS to HRS). Resistive switching occurs as a result of the diffusion and removal of the oxygen functional groups in the GO film caused by Joule heating induced by the electric current. Complete electrical characterization tests are presented along with wettability and X-ray diffraction (XRD) tests. This work opens a new vision for realizing rGO-based MR devices with tunable switching properties, broadening the application horizon of the device.

Artificial Neurons and Synapses Based on Al/a-SiNxOy:H/P+-Si Device with Tunable Resistive Switching from Threshold to Memory.

As the building block of brain-inspired computing, resistive switching memory devices have recently attracted great interest due to their biological function to mimic synapses and neurons, which displays the memory switching or threshold switching characteristic. To make it possible for the Si-based artificial neurons and synapse to be integrated with the neuromorphic chip, the tunable threshold and memory switching characteristic is highly in demand for their perfect compatibility with the mature CMOS technology. We first report artificial neurons and synapses based on the Al/a-SiNxOy:H/P+-Si device with the tunable switching from threshold to memory can be realized by controlling the compliance current. It is found that volatile TS from Al/a-SiNxOy:H/P+-Si device under the lower compliance current is induced by the weak Si dangling bond conductive pathway, which originates from the broken Si-H bonds. While stable nonvolatile MS under the higher compliance current is attributed to the strong Si dangling bond conductive pathway, which is formed by the broken Si-H and Si-O bonds. Theoretical calculation reveals that the conduction mechanism of TS and MS agree with P-F model, space charge limited current model and Ohm’s law, respectively. The tunable TS and MS characteristic of Al/a-SiNxOy:H/P+-Si device can be successfully employed to mimic the biological behavior of neurons and synapse including the integrate-and-fire function, paired-pulse facilitation, long-term potentiation and long-term depression as well as spike-timing-dependent plasticity. Our discovery supplies an effective way to construct the neuromorphic devices for brain-inspired computing in the AI period.

Tunable Resistive Switching in Shales

Tunable Resistive Switching in Shales

A two-dimensional polymer memristor based on conformational changes with tunable resistive switching behaviours

A resistive switching memory device based on a 2DPTPAK+TAPB film with the conformational change mechanism was prepared and the memory behaviors can be adjusted by the degree of conformational changes.

Stable photovoltaic output and optically tunable resistive switching in all-inorganic flexible ferroelectric thin film with self-polarization characteristic

The immense potential of photo-electrical materials applied in intelligent and wearable electronic devices has motivated many researches on flexible ferroelectric thin film. However, how to enhance stability of output and achieve multifunction is still a challenge. Here, an all-inorganic flexible ferroelectric thin film with Au/Bi2FeMo0.7Ni0.3O6/LaNiO3/Nickel foil structure is prepared by sol-gel method. The thin film exhibits excellent photovoltaic stability. The change rates of the short circuit currents and open circuit voltages are less than 5% in different bending states and after bending-releasing cycles, which is attributed to its stable self-polarization characteristic. Furthermore, an optically tunable resistive switching behavior is found in the thin film. The switching voltages and ON/OFF ratio of resistance can be tuned in real time by on-off control of light, demonstrating a correlation between resistive switching and photovoltaic effect. It is proposed that the photovoltaic effect modulates the energy band structure of the thin film, leading to an increased ON/OFF ratio of resistance. This work opens up a promising route to the development of multifunctional flexible photo-electrical materials.

Flexible Artificial Memristive Synapse Constructed from Solution‐Processed MgO–Graphene Oxide Quantum Dot Hybrid Films

AbstractInspired by the low energy consumption and highly parallel processing power of the biological neuromorphic system, the development of a brain‐inspired computing paradigm with electronic devices based artificial synapse may play an essential role in eliminating the Von Neumann bottleneck. Among candidate electronic devices, memristive devices have shown great potential for artificial synapse because of its tunable resistive switching (RS) behaviors. Herein, a biological synapse with solution‐processed MgO‐graphene oxide quantum dots (MgO‐GOQDs) based memristor is developed. The device exhibits highly controllable RS behavior owing to the enhancement of the local electric field by GOQDs and redox of GOQDs under electric fields. Moreover, essential biosynaptic functions including paired‐pulse facilitation, short‐term plasticity (STP)/long‐term plasticity (LTP), STP to LTP transition, and spike‐time‐dependent plasticity are successfully emulated. It is noteworthy that the device fabricated on a polyethylene terephthalate substrate also presents stable RS behavior after a large number of bending cycles. This study demonstrates the great potential of solution‐processed MgO–GOQD hybrid film on its application for the realization of flexible artificial neural networks.

Optically triggered multilevel resistive switching characteristics of Cu/MoS2/AlN/ITO bilayer memory structure

In this work, the tunable resistive switching (RS) functionality of a Cu/MoS2/AlN/ITO nanostructured device is systematically investigated in dark and white light illumination. The device exhibits bi-state RS behavior in the dark ambient, whereas light illumination induces an extra intermediate resistance state and provides controllable tri-state RS characteristics. A conceptual model is proposed and discussed to elucidate the origin of the switching behavior of two resistance states and multiple resistance states of the device. Under the dark ambient condition, the high resistance state and the low resistance state in the device could be ascribed to the formation/rupture of a Cu metallic filamentary path between the electrodes. However, the formation of an additional ionic filament via trapping/detrapping of electrons in nitride-sulfide-related vacancies along with the Cu metallic filament is responsible for the tri-state switching under the light illumination. Interestingly, the variation of SET voltage with applied light intensity has also been demonstrated. The calculated value of the temperature coefficient and temperature dependency of resistance in various resistance states confirms the existence of the proposed model. The device performed a good undispersed endurance up to 1.5 × 103 cycles and stable retention over 103 s at room temperature. This optical activity dependent functionality of the device provides a possibility to extend resistive switching-based nonvolatile random access memory applications to the optical domain such as imaging sensors, photodetectors, and optoelectronic switches.

Tunable resistive switching of vertical ReSe2/graphene hetero-structure enabled by Schottky barrier height and DUV light

The development of the novel three-terminal hybrid lateral memristor and transistor device called memtransistor, has successfully provided additional functionalities in memory devices. However, their high operating voltage is critical. In this report, we have utilized the vertical heterojunction of Copper/Rhenium diselenide/Graphene to obtain low power gate tunable memristor. In such devices, resistive switching is governed by barrier height at the Rhenium diselenide/Graphene) interface, which controls the flow of electrons to neutralize Cu ions for the formation of the Cu filament. Therefore, barrier height is manipulated from ∼60 meV at Vg = 90 V to ∼828 meV at Vg = - 90 V by tuning the work function of the mono layer graphene with back-gate voltages. Subsequently, the tuning of barrier height ultimately modulates the operating voltage from 0.53 V to 3.67 V and Ron/Roff ratio from 102 to 105 by changing the Vg from 90 V to −90 V respectively. Moreover, the deep ultraviolet light assisted resistance switching effect is also investigated in gate-controlled Copper/Rhenium diselenide/Graphene devices. Thus, gate modulation and deep ultraviolet light irradiation make it compatible for future application in integrated optoelectronic systems.

Water-Mediated Ionic Migration in Memristive Nanowires with a Tunable Resistive Switching Mechanism.

Memristive devices based on electrochemical resistive switching effects have been proposed as promising candidates for in-memory computing and for the realization of artificial neural networks. Despite great efforts toward understanding the nanoionic processes underlying resistive switching phenomena, comprehension of the effect of competing redox processes on device functionalities from the materials perspective still represents a challenge. In this work, we experimentally and theoretically investigate the concurring reactions of silver and moisture and their impact on the electronic properties of a single-crystalline ZnO nanowire (NW). A decrease in electronic conductivity due to surface adsorption of moisture is observed, whereas, at the same time, water molecules reduce the energy barrier for Ag+ ion migration on the NW surface, facilitating the conductive filament formation. By controlling the relative humidity, the ratio of intrinsic electronic conductivity and surface ionic conductivity can be tuned to modulate the device performance. The results achieved on a single-crystalline memristive model system shed new light on the dual nature of the mechanism of how moisture affects resistive switching behavior in memristive devices.

Ferroelectric Memristors Based Hardware of Brain Functions for Future Artificial Intelligence

Brain-inspired neuromorphic computing systems have long attracted significant interests to replace the conventional Von-Neumann systems because the development of big data analysis and artificial intelligence has put forward higher requirements for computing speed and energy consumptions. Memristive devices are known as one of the most significant candidates to implement brain-inspired neuromorphic computing systems due to their special properties to emulate biological synapses of human brains. Ferroelectric material is a breakthrough for the resistive-switching layer of memristors due to their continuously tunable resistive switching behaviors. However, the application of ferroelectric memristors is limited by unstable performance and the low switching ratio. In this work, ferroelectric memristors have been fabricated and two-dimensional (2D) material MXene (Ti3C2) has been firstly introduced to the Cu/PZT/Pt devices. The insertion of MXene can enhance the performance of the devices by boosting the formation of conductive filaments of oxygen vacancies. The Cu/MXene/PZT/Pt devices exhibit stable resistive switching phenomena and have a high switching ratio about 106. The resistance of Cu/MXene/PZT/Pt memristors can be regulated under continuous voltage pulses. More interestingly, some synaptic functions have been successfully mimicked using Cu/MXene/PZT/Pt memristors. This work will pave the way for the development of the implementation of brain-inspired computing systems.

Multifunctional Polymer Memory via Bi-Interfacial Topography for Pressure Perception Recognition.

Emerging memory devices, that can provide programmable information recording with tunable resistive switching under external stimuli, hold great potential for applications in data storage, logic circuits, and artificial synapses. Realization of multifunctional manipulation within individual memory devices is particularly important in the More‐than‐Moore era, yet remains a challenge. Here, both rewritable and nonerasable memory are demonstrated in a single stimuli‐responsive polymer diode, based on a nanohole‐nanowrinkle bi‐interfacial structure. Such synergic nanostructure is constructed from interfacing a nanowrinkled bottom graphene electrode and top polymer matrix with nanoholes; and it can be easily prepared by spin coating, which is a low‐cost and high‐yield production method. Furthermore, the resulting device, with ternary and low‐power operation under varied external stimuli, can enable both reversible and irreversible biomimetic pressure recognition memories using a device‐to‐system framework. This work offers both a general guideline to fabricate multifunctional memory devices via interfacial nanostructure engineering and a smart information storage basis for future artificial intelligence.

Wavelength dependent light tunable resistive switching graphene oxide nonvolatile memory devices

This paper reports on the first optically tunable graphene oxide memristor device. Modulation of resistive switching memory by light opens the route to new optoelectronic devices that can be switched optically and read electronically. Applications include integrated circuits with memory elements switchable by light and optically reconfigurable and tunable synaptic circuits for neuromorphic computing and brain-inspired, artificial intelligence systems. In this report, planar and vertical structured optical resistive switching memristors based on graphene oxide are reported. The device is switchable by either optical or electronic means, or by a combination of both. In addition the devices exhibit a unique wavelength dependence that produces reversible and irreversible properties depending on whether the irradiation is long or short wavelength light, respectively. For long wavelength light, the reversible photoconductance effect permits short-term dynamic modulation of the resistive switching properties of the light, which has application as short-term memory in neuromorphic computing. In contrast, short wavelength light induces both the reversible photoconductance effect and an irreversible change in the memristance due to reduction of the graphene oxide. This has important application in the fabrication of cloned neural networks with factory defined weights, enabling the fast replication of artificial intelligent chips with pre-trained information.

Tunable Resistive Switching Enabled by Malleable Redox Reaction in the Nano-Vacuum Gap.

Neuromorphic computing has emerged as a highly promising alternative to conventional computing. The key to constructing a large-scale neural network in hardware for neuromorphic computing is to develop artificial neurons with leaky integrate-and-fire behavior and artificial synapses with synaptic plasticity using nanodevices. So far, these two basic computing elements have been built in separate devices using different materials and technologies, which poses a significant challenge to system design and manufacturing. In this work, we designed a resistive device embedded with an innovative nano-vacuum gap between a bottom electrode and a mixed-ionic-electronic-conductor (MIEC) layer. Through redox reaction on the MIEC surface, metallic filaments dynamically grew within the nano-vacuum gap. The nano-vacuum gap provided an additional control factor for controlling the evolution dynamics of metallic filaments by tuning the electron tunneling efficiency, in analogy to a pseudo-three-terminal device, resulting in tunable switching behavior in various forms from volatile to nonvolatile switching in a single device. Our device demonstrated cross-functions, in particular, tunable neuronal firing and synaptic plasticity on demand, providing seamless integration for building large-scale artificial neural networks for neuromorphic computing.

Photoresponse of nonvolatile resistive memory device based on all-inorganic perovskite CsPbBr3 nanocrystals

In this work, the resistive memory devices were fabricated based on all-inorganic CsPbBr3 nanocrystals (NCs) embedded into the insulating polymethylmethacrylate (PMMA) with a configuration of Au/PMMA/PMMA: CsPbBr3 NCs/PMMA/indium tin oxide (ITO). The as-fabricated devices exhibit forming-free bipolar resistive switching with resistance ratio of HRS to LRS (RH/L) evolving from metastable 106 to stable 10. In HRS with high RH/L, the devices witness the prompt photoresponse under light illumination of 365 nm, 405 nm, 420 nm, and 500 nm. Also, set voltages of resistive switching with low RH/L can be reduced by the illumination. Furthermore, the resistive switching and photoresponse of Au/PMMA/PMMA: CsPbBr3 NCs/PMMA/ITO devices were elucidated by considering the photosensitive property and role of trapping/de-trapping centers of CsPbBr3 NCs. This work suggests the tunable resistive switching of Au/PMMA/PMMA: CsPbBr3 NCs/PMMA/ITO devices through light illumination, and controllable photoresponse by resistive states.

Electric Field Control of Phase Transition and Tunable Resistive Switching in SrFeO2.5.

SrFeO x (SFO x) compounds exhibit ionic conduction and oxygen-related phase transformation, having potential applications in solid oxide fuel cells, smart windows, and memristive devices. The phase transformation in SFO x typically requires a thermal annealing process under various pressure conditions, hindering their practical applications. Here, we have achieved a reversible phase transition from brownmillerite (BM) to perovskite (PV) in SrFeO2.5 (SFO2.5) films through ionic liquid (IL) gating. The real-time phase transformation is imaged using in situ high-resolution transmission electron microscopy. The magnetic transition in SFO2.5 is identified by fabricating an assisted La0.7Sr0.3MnO3 (LSMO) bottom layer. The IL-gating-converted PV phase of a SrFeO3-δ (SFO3-δ) layer shows a ferromagnetic-like behavior but applies a huge pinning effect on LSMO magnetic moments, which consequently leads to a prominent exchange bias phenomenon, suggesting an uncompensated helical magnetic structure of SFO3-δ. On the other hand, the suppression of both magnetic and exchange coupling signals for a BM-phased SFO2.5 layer elucidates its fully compensated G-type antiferromagnetic nature. We also demonstrated that the phase transition by IL gating is an effective pathway to tune the resistive switching parameters, such as set, reset, and high/low-resistance ratio in SFO2.5-based resistive random-access memory devices.