Typical Bipolar Resistive Switching Research Articles

Implementation of Artificial Synapse Using IGZO-Based Resistive Switching Device.

In this study, we present the resistive switching characteristics and the emulation of a biological synapse using the ITO/IGZO/TaN device. The device demonstrates efficient energy consumption, featuring low current resistive switching with minimal set and reset voltages. Furthermore, we establish that the device exhibits typical bipolar resistive switching with the coexistence of non-volatile and volatile memory properties by controlling the compliance during resistive switching phenomena. Utilizing the IGZO-based RRAM device with an appropriate pulse scheme, we emulate a biological synapse based on its electrical properties. Our assessments include potentiation and depression, a pattern recognition system based on neural networks, paired-pulse facilitation, excitatory post-synaptic current, and spike-amplitude dependent plasticity. These assessments confirm the device's effective emulation of a biological synapse, incorporating both volatile and non-volatile functions. Furthermore, through spike-rate dependent plasticity and spike-timing dependent plasticity of the Hebbian learning rules, high-order synapse imitation was done.

Occurrence of robust memristive behavior for low-power transient resistive switching and photo-responsive neuromorphic computing in low-dimensional perovskite

Recent progress on the memristive devices owing to the multi-functional approach have surged the exploration of new functional materials. Here, we have incorporated two-dimensional (2D) halide perovskite in memristive device. The Pb-free Cs3Bi2I9 perovskite active layer was fabricated to obtain the ITO/Cs3Bi2I9/Pt structure. The device shows typical bipolar resistance switching behavior with Off state resistance in TΩ scale. Due to the higher work function of the top Pt electrode, the barrier height at the Pt/Cs3Bi2I9 junction is higher and the observed device conductance is low in the Off state. Enhanced memory parameters such as endurance (>103 cycles) and retention (104 s) for multiple conductance states is observed. In the pulse modulated synaptic characterization, the device emulated essential post-synaptic plasticity, short-term and long-term potentiation with power consumption in femto Joule. The classical conditioning learning was mimicked by the device by electric and optical stimulation procuring basic associative training. The non-toxicity of the perovskite material has been successfully utilized for the transient memristor application. The robust in-memory photonic memristive property of the device along with water stimulated transient behavior demonstrates the significance of the proposed device in multi-dimensional field of electronic device.

Co-existence of digital and analog resistive switching in 2D layered BiOI nanosheets for synaptic applications

The emulation of the biological synapses is essential for brain-inspired computing which is expected to overcome the traditional von Neumann bottleneck. Thus, synaptic memristor with analog resistive switching (RS) is highly desirable in non-volatile memristors for future neuromorphic computing. Herein, the co-existence of digital and analog RS can be observed in two-dimensional (2D) layered BiOI nanosheets sandwiched by the top and bottom Pt electrodes. The vertical Pt/BiOI/Pt memristors demonstrate typical bipolar RS behaviors with a large ON/OFF ratio of 1.0 × 103 and long retention time up to 1.6 × 104 s under a relatively large operation voltage. When the operation voltages are reduced to 1 V, analog RS behaviors with a series of tunable resistance states can be observed. The adjustable resistance states can be utilized to emulate “learning-forgetting” experience of human brain. Repeatable long-term potentiation (LTP) and long-term depression (LTD) cycles can be implemented based on the synaptic memristors, which can be used for simulation of artificial neural network for image recognition with accuracy up to 91.15 %. Moreover, Pavlov’s dog experiment is successfully emulated based on the synaptic memristors. This study suggests good prospects of the synaptic memristors based on BiOI nanosheets for future neuromorphic computing.

Lead-free CsCu2Br3 perovskite for multilevel resistive switching memory

Organic–inorganic metal halide perovskites have recently attracted enormous interest in the field of resistive switching memories owing to their unique electrical properties. Unfortunately, two challenges, the inadequate long-term stability and the toxicity of lead, largely hinder their further practical application. Herein, a 1D all-inorganic lead-free CsCu2Br3 perovskite is proposed for resistive switching devices to resolve these issues. The CsCu2Br3-based resistive switching devices exhibit typical bipolar resistive switching behavior with low set voltage, high on/off ratio (103), stable retention properties (>2 × 104 s), and endurance (200 cycles) in air. The unencapsulated CsCu2Br3-based device still maintains resistive switching characteristics while stored in ambient environment for over 2 months. Moreover, four on-state multilevel information storage behavior has been observed by regulating the value of compliance current during set process. The resistive switching behavior is dominated by the formation and fracture of conductive filaments, which are induced by the movement of Br− ions under electrical bias. This work offers the opportunity and strategy for the design of air-stable and environment-friendly metal halide perovskite-based memory devices.

Electrochemical Resistive Switching in Nanoporous Hybrid Films by One-Step Molecular Layer Deposition.

An organic-inorganic hybrid resistive random-access memory based on a nanoporous zinc-based hydroquinone (Zn-HQ) thin film has been constructed with a Pt/Zn-HQ/Ag sandwich structure. The porous Zn-HQ functional layer was directly fabricated by a one-step molecular layer deposition. These Pt/Zn-HQ/Ag devices show a typical electroforming-free bipolar resistive switching characteristic with lower operation voltages and higher on/off ratio above 102. Our nanoporous hybrid devices can also realize multilevel storage capability and exhibit excellent endurance/retention properties. The connection and disconnection of Ag conductive filaments in nanoporous Zn-HQ thin film follow the electrochemical metallization mechanism. Our computational simulations confirm that the existence of nanopores in Zn-HQ thin films facilitates the Ag filament formation, contributing to the high performance of our hybrid devices.

High-performance and humidity robust multilevel lead-free all-inorganic Cs3Cu2Br5 perovskite-based memristors

Halide perovskites have attracted surge of interest in the memristor field due to their superior electrical property and corresponding remarkable device performances. However, the issues of toxicity and unstable properties still severely restrict their potential applications. Here, the lead-free all-inorganic perovskite Cs3Cu2Br5 films are adopted as the switching layer to fabricate memristors with Al/Cs3Cu2Br5/ITO structure. The prepared Al/Cs3Cu2Br5/ITO memristors exhibit typical reproducible bipolar resistive switching (RS) behavior with striking characteristics, including ultralow operating voltages (0.45, −0.39 V), moderate high resistance state/low resistance state ratio (≈102), and remarkable retention time (>104 s). In addition, the multilevel storage capability can be achieved by controlling compliance current. The RS effect, stemming from the formation/rupture of both localized conductive Br vacancy/Al atom filaments, is proposed to illustrate the memristors. More importantly, the RS behavior of Al/Cs3Cu2Br5/ITO memristors maintains robustness in harsh environments with humidity up to 80%, enabling secure hardware applicable in extreme environments. This work demonstrates the opportunity for exploring the next-generation nonvolatile memories based on lead-free all-inorganic halide perovskites in future environmental-friendly and humidity robust electronics.

Dimer-type Cs3Sb2I9: An efficient perovskite material for low operating voltage and high stability flexible resistive switching memory

All-inorganic perovskites have been taken as the promising functional materials in non-volatile resistive switching (RS) memory. Herein, the lead-free all-inorganic Cs3Sb2I9 perovskites with high stability are fabricated via hydrochloric acid (HCl) assisted solution method at low-temperature. The devices with a structure of Ag/polymethyl methacrylate (PMMA)/HCl-modified dimer-Cs3Sb2I9/ITO take on typical bipolar RS behavior and remarkable characteristics such as high ON/OFF ratio (≈66), low operating voltage (≈ −0.34 V/+0.25 V), excellent endurance property (≥120 cycles) and long data retention (≥104 s). Moreover, outstanding mechanical stability of the Cs3Sb2I9-based flexible memory devices are demonstrated under different bending angles and over consecutive 103 bending cycles. In addition, the Cs3Sb2I9-based memory devices show no obvious change in the RS behavior after over 10 days storage under an ambient atmosphere. This work will contribute to understanding the characteristics of low operating voltage and high stability RS behavior of the all-inorganic perovskites, and illuminate the great application potential of the lead-free antimony-based perovskite materials in next generation low power consumption non-volatile flexible memory devices.

Visible-light irradiation improved resistive switching characteristics of a 2D Cs2Pb(SCN)2I2-Based memristor device

Two-dimensional (2D) perovskite materials show enormous potential in optoelectronic applications owing to their exceptional thermal stability and unique lattice structures. However, research into anion-substituted 2D perovskites is relatively rare, particularly in the photoelectric information storage field. Here, an anion-based 2D perovskite Cs2Pb(SCN)2I2 film with high orientation and high thermal-stability is achieved by simple low-temperature solution processing and the memristor of Al/Cs2Pb(SCN)2I2/FTO is established. The experimental evidence shows that: 1) In the absence of light irradiation, memristors present typical bipolar resistance switching behaviour with On/Off resistance ratio (>103) and reliable retention (>104 s); 2) By introducing light irradiation, it can achieve a more dependable memristor with decreased RS fluctuation and improved cycling endurance. In addition, by modifying the compliance current (Icc), it can realize multi-level storage function of memories with good high temperature endurance. Finally, the logic gate function is also demonstrated with these cells. The operational principles of memristor devices are comprised of the charge trapping and conductive filament mechanisms. The light irradiation reduces the ion migration barrier and enhances the conductivity of perovskite films, thus limiting the excessive growth of conductive filaments. This work offers the groundwork for creating anionic two-dimensional perovskite photoelectric memristor devices.

Anodic Sb2S3 electrodeposition from a single source precursor for resistive random-access memory devices

In this paper we report the use of Na3[SbS4].9H2O as a single source precursor for the electrodeposition of Sb2S3 from aqueous electrolyte at pH 9.1. We present the electrochemistry of the [SbS4]3− anion and the redox processes observed for the deposited Sb2S3 film. We show that an amorphous Sb2S3 film can be deposited by anodic electrodeposition onto glassy carbon and that the by-product that accompanies this deposition can be avoided by using a suitable pulse plating approach. Raman spectroscopy and grazing incidence X-ray diffraction were used to characterise the deposits and to show that good quality crystalline films of Sb2S3 are produced on annealing.The crystalline Sb2S3 films were screened for application in Resistive Random-Access Memory, and it was demonstrated that crystalline Sb2S3 films display typical bipolar resistive switching behaviour, and that the resistance ratio between the high resistance state and the low resistance state is approximately one order of magnitude at 1.5 V, which is sufficient for memory applications. A mechanism for the resistive switching is also proposed.

Enhancement of resistive switching behavior of organic resistive random access memory devices through UV-Ozone treatment

We fabricated organic resistive random-access memory (RRAM) devices using a low-cost solution-process method. All the processes were performed at temperatures below 135 °C under ambient atmospheric conditions. The RRAM resistive switching layer was formed from a polymer-fullerene bulk heterojunction using poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The fabricated organic RRAM device exhibited typical nonvolatile bipolar resistive switching behavior with an ON/OFF ratio of ∼40, but it provided a low endurance of 27 cycles. Therefore, for enhanced stability, simple UV–Ozone (UVO) treatment was applied to the P3HT:PCBM organic bulk heterojunction layer. The organic RRAM device with UVO treatment exhibited an enhanced performance with an ON/OFF ratio of ∼400 and an endurance of 47 cycles. In addition, complementary resistive switching behavior was observed. The conduction mechanisms of the organic RRAM device were investigated by fitting the measured I–V data to numerical equations, and Schottky emission and Ohmic conduction were the main conduction mechanisms for the high-resistance and low-resistance states for the RRAM device with or without UVO treatment.

Transparent, Flexible, and Low-Operating-Voltage Resistive Switching Memory Based on Al2O3/IZO Multilayer.

In this study, a different number of indium zinc oxide (IZO) interlayers are fabricated into Al2O3‐based transparent resistive switching memory on a transparent indium tin oxide (ITO)/glass substrate at room temperature. Al2O3/IZO multilayer transparent memory has a transmittance of at least 65% in the wavelength range of 400–900 nm. In addition, the Al2O3/IZO multilayer transparent memory can achieve an electroforming voltage that is 35.7% lower than that of ITO/pure‐Al2O3/IZO transparent memory. The fabricated Al2O3/IZO multilayer transparent memory exhibits typical bipolar resistive switching behavior, regardless of the number of IZO interlayers. Also, the fabricated Al2O3/IZO multilayer transparent memory has a low operating voltage within ±1.5 V. In addition, a flexible Al2O3/IZO multilayer transparent memory is fabricated using the same process on ITO‐coated polyethylene terephthalate. The fabricated flexible transparent memory also maintains the resistive switching characteristics during the bending state.

High performance and low power consumption resistive random access memory with Ag/Fe2O3/Pt structure

Due to magnetic field tunability and the abundance of iron in the Earth’s crust, iron oxide-based resistive random access memory (RRAM) is considered to be low cost and potential for multi-level storage. However, the relatively high operation voltage (>1 V) and small storage window (<100) limit its application. In this work, the devices with simple Ag/Fe2O3/Pt structure exhibit typical bipolar resistive switching with ultralow set voltage (V set) of 0.16 V, ultralow reset voltage (V reset) of −0.04 V, high OFF/ON resistance ratio of 103, excellent cycling endurance more than 104 and good retention time longer than 104 s. Each major parameter has about an order of magnitude improvement compared to the previous data. The devices demonstrate outstanding stable low power consumption quality. Based on the analysis of the experimental results, a percolation model of silver ion migration was established and confirmed that low operation voltage is attributed to the amorphous oxide layer with large porosity. During electrical testing, the compliance current (I c) and maximum reset voltage (V max) can also affect the device performance. This discovery suggests Fe2O3 memristor has significant potential for application and provides a new idea for the realization of high-performance low-power RRAM.

Performance variation of solution-processed memristor induced by different top electrode

Al/TE (top electrode)/AlOx/Pt RRAM (resistive random access memory) devices with solution-processed spin-coated AlOx layers annealed at various temperatures (225/250/275 °C) exhibited typical bipolar resistive switching performance with low SET/RESET voltage (<4 V), larger ON/OFF ratio (>103) and excellent stability (retention time over 104 s and endurance cycles more than 100). Ni and TiN were chosen as the TE, respectively. Better RS characteristics were obtained on Ni/AlOx/Pt RRAM devices with lower operating voltage and better stability. In addition, the voltage variation between Ni/AlOx/Pt and TiN/AlOx/Pt RRAM devices was investigated. Compared with Ni/AlOx/Pt RRAM devices, TiN/AlOx/Pt devices operated with higher operation voltage at various annealing temperatures, which indicated the influence of work function difference (△ΦM) between TE and BE (bottom electrode). The greater the △ΦM, the more energy consumption and the higher operation voltage were demanded.

Negative Photoconductance Effect: An Extension Function of the TiOx‐Based Memristor

AbstractThe negative photoconductance (NPC) effect, defined as an increase in resistance upon exposure to illumination, holds great potential for application in photoelectric devices. A prepared memristor with the structure of Ag|graphene quantum dots (GQDs)|TiOx|F‐doped SnO2 exhibits typical bipolar resistive switching (RS) memory behavior. The NPC effect is impressively observed in the high resistance state branch of the RS memory, enabling the memristor function to be extended to both memory logic display and multistate data storage. The observed NPC effect is attributed to the excitation, migration, and compensation of oxygen vacancy at the GQDs/TiOx interface, at which the electron transportation is efficiently restricted because of the variation in the charge distribution and electrostatic potential under illumination. Experiments, theoretical calculations, and physical models are used to provide engineer the interface with the aim of building the NPC effect in the memristive device. These results unveil a new horizon on extending the functionality of the memristor.

Room-Temperature, Solution-Processed SiOx via Photochemistry Approach for Highly Flexible Resistive Switching Memory.

Due to its high versatility and cost-effectiveness, solution process has a remarkable advantage over physical or chemical vapor deposition (PVD/CVD) methods in developing flexible resistive random-access memory (RRAM) devices. However, the reported solution-processed binary oxides, the most promising active layer materials for their compatibility with silicon-based semiconductor technology, commonly require high-temperature annealing (>145 °C) and the RRAMs based on them encounter insufficient flexibility. In this work, an amorphous and uniform SiOx active layer was prepared by irradiating an inorganic polymer, perhydropolysilazane, with a vacuum ultraviolet of 172 nm at room temperature. The corresponding RRAM showed typical bipolar resistance switching with a forming-free behavior. The device on polyimide film exhibited outstanding flexibility with a minimum bending radius of 0.5 mm, and no performance degradation was observed after bending 2000 times with a radius of 2.3 mm, which is the best among the reported solution-processed binary oxide-based RRAMs and can even rival the performance of PVD/CVD-based devices. This room-temperature solution process and the afforded highly flexible RRAMs have vast prospects for application in smart wearable electronics.

Study on Multilevel Resistive Switching Behavior With Tunable ON/OFF Ratio Capability in Forming-Free ZnO QDs-Based RRAM

Resistive random access memories (RRAMs) have attracted tremendous attention due to their miniaturized size, low power consumption, high response speed, and simple fabrication requirements, which are regarded as a promising candidate for future nonvolatile memories. However, the traditional binary storage RRAMs fail to meet the high-density requirement in the area of big data. One of the ways to overcome this obstacle is to realize multilevel state transitions in a unit RRAM. Herein, we propose a facile spin-coating method to develop a multilevel RRAM based on Al/poly(methyl methacrylate) (PMMA)/ZnO quantum dots (QDs)/PMMA/ZnO QDs/PMMA/fluorine-doped tin oxide (FTO) structure, with the significant merits of typical forming-free bipolar resistive switching behavior, low-power operating voltage, stable endurance, and excellent retention. In specific, the ON/OFF ratio of the proposed ZnO QDs-based device can be adjusted by tuning the concentration of the ZnO QDs. Moreover, a multilevel RRAM performance with distinct four-level resistance states is obtained by varying the compliance current, which demonstrates that the proposed device has a specific application in multilevel data storage. The conductive filament model, combining the enhanced internal field and robust formation of the conductive filament, is introduced to explain the mechanism of the resistive switching behavior and multilevel performance. This work paves a new way for its prospect in constructing high-density data storage RRAMs.

Effect of film thickness and temperature on the resistive switching characteristics of the Pt/HfO2/Al2O3/TiN structure

Thin films with HfO2/Al2O3 laminated structure were prepared by the ALD method in this paper. Typical bipolar resistance switching characteristics were observed in the Pt/HfO2/Al2O3/TiN structure device. The samples were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The effects of dielectric thickness and different test temperatures on the electrical performance were investigated. Experiments show that when the thickness of HfO2/Al2O3 is 7 nm/3 nm, the electrical properties are the best. As the test temperature increases, the resistance values (RLRS and RHRS) of the Pt/HfO2/Al2O3/TiN structure fluctuate more and more. When the test temperature approaches the failure temperature, the device's transition voltages (VSet and VReset) will also become more volatile.

Resistive Switching Characteristics of Nonvolatile Memory with HSQ Film Using Microwave Irradiation.

In this study, we fabricated a resistive random access memory (ReRAM) of metal-insulator-metal structures using a hydrogen silsesquioxane (HSQ) film that was deposited by a low-cost solution process as a resistance switching (RS) layer. For post-deposition annealing (PDA) to improve the switching performance of HSQ-based ReRAMs, we applied high energy-efficient microwave irradiation (MWI). For comparison, ReRAMs with an as-deposited HSQ layer or a conventional thermally annealed (CTA) HSQ layer were also prepared. The RS characteristics, molecular structure modification of the HSQ layer, and reliability of the MWI-treated ReRAM were evaluated and compared with the as-deposited or CTA-treated devices. Typical bipolar RS (BRS) behavior was observed in all the fabricated HSQ-based ReRAM devices. In the low-voltage region of the high-resistance state (HRS) as well as the low-resistance state, current flows through the HSQ layer by an ohmic conduction mechanism. However, as the applied voltage increases in HRS, the current slope increases nonlinearly and follows the Poole-Frenkel conduction mechanism. The RS characteristics of the HSQ layer depend on the molecular structure, and when the PDA changes from a cage-like structure to a cross-linked network, memory characteristics are improved. In particular, the MWI-treated HSQ ReRAM has the largest memory window at the smallest operating power and demonstrated a stable endurance during the DC cycling test over 500 times and reliable retention at room (25 °C) and high (85 °C) temperatures for 10⁴ seconds.

Investigation of Conductive Mechanism of Amorphous IGO Resistive Random-Access Memory with Different Top Electrode Metal

In this paper, resistive random-access memory (RRAM) with InGaO (IGO) as an active layer was fabricated by radio-frequency (RF) sputtering system and the resistive switching mechanism with the different top electrode (TE) of Pt, Ti, and Al were investigated. The Pt/IGO/Pt/Ti RRAM exhibits typical bipolar resistive switching features with an average set voltage of 1.73 V, average reset voltage of −0.60 V, average high resistance state (HRS) of 54,954.09 Ω, and the average low resistance state (LRS) of 64.97 Ω, respectively. Ti and Al were substituted for Pt as TE, and the conductive mechanism was different from TE of Pt. When Ti and Al were deposited onto the switching layer, both TE of Ti and Al will form oxidation of TiOx and AlOx because of their high activity to oxygen. The oxidation will have different effects on the forming of filaments, which may further affect the RRAM performance. The details of different mechanisms caused by different TE will be discussed. In brief, IGO is an excellent candidate for the RRAM device and with the aids of TiOx, the set voltage, and reset voltage, HRS and LRS become much more stable.

Dependence of InGaZnO and SnO2 thin film stacking sequence for the resistive switching characteristics of conductive bridge memory devices

We have investigated the switching mechanism of conductive bridge random access memory (CBRAM) with Ag/SnO2/Pt, Ag/InGaZnO(IGZO)/Pt and their hybrid oxide devices with different stacking sequence (Ag/SnO2/IGZO/Pt and Ag/IGZO/SnO2/Pt). Typical bipolar resistive switching is observed in single layered devices and an Ag/SnO2/IGZO/Pt hybrid device. Interestingly, a stable and reproducible unipolar resistive switching is observed for a hybrid device with a stacking sequence of Ag/IGZO/SnO2/Pt. This result suggests that the staking sequence of dielectrics in the IGZO and SnO2 electrolyte determines unipolar or bipolar switching. The different switching types in the hybrid electrolyte are based on different migration or diffusion rates of Ag ions in the solid electrolyte and redox reaction rates at the electrodes. And as compared to single layered devices, the hybrid structured devices exhibit low operation voltages, higher ION/IOFF ratio, uniform switching cycles and better endurance and retention characteristics. The results and switching mechanisms demonstrated here in hybrid devices can be extended to other hybrid devices based on CBRAM device.