Resistive Switching Characteristics Research Articles

Implication Logic Circuit Based on a Graphene Oxide Complementary Resistive Switching Device

AbstractThe logic circuit is the main component of an integrated circuit chip that dictates the operation and performance of the chip. The logic circuit based on a memristor can improve the integration and operation speed of the existing integrated circuit and reduce the chip size and the number of devices used by a single logic circuit. However, most of the research on logic circuits based on memristors has focused only on simulations, and research on the realization of logic circuits by hardware using actual memristors is limited. In this paper, a memristor based on graphene oxide with stable complementary resistive switching characteristics is fabricated, a logic circuit is built by using this device, and the logic functions of “IMP,” “AND,” and “NOR” are successfully realized. The complementary resistive switching device can alleviate the severe power loss caused by the memory separation of the von Neumann architecture. Moreover, its unique structure enables it to realize material logic independently without the use of multiple memristors and resistors, providing a new scheme for the physical realization of logic circuits. It also opens up a new path for integrated chips to break through von Neumann architecture.

Multilevel resistive switching in hydrothermally synthesized FeWO4 thin film-based memristive device for non-volatile memory application

The memristors offer significant advantages as a key element in non-volatile and brain-inspired neuromorphic systems because of their salient features such as remarkable endurance, ability to store multiple bits, fast operation speed, and extremely low energy usage. This work reports the resistive switching (RS) characteristics of the hydrothermally synthesized iron tungstate (FeWO4) based thin film memristive device. The detailed physicochemical analysis was investigated using Rietveld’s refinement, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) techniques. The fabricated Ag/FWO/FTO memristive device exhibits bipolar resistive switching (BRS) behavior. In addition, the devices exhibit negative differential resistance (NDR) at both positive and negative bias. The charge-flux relation portrayed the non-ideal or memristive nature of the devices. The reliability in the RS process was analyzed in detail using Weibull distribution and time series analysis techniques. The device exhibits stable and multilevel endurance and retention characteristics which demonstrates the suitability of the device for the high-density non-volatile memory application. The current conduction of the device was dominated by Ohmic and trap controlled-space charge limited current (TC-SCLC) mechanisms and filamentary RS process responsible for the BRS in the device. In a nutshell, the present investigations reveal the potential use of the iron tungstate for the fabrication of memristive devices for the non-volatile memory application.

Stable and repeatable ZrO2 RRAM achieved by NiO barrier layer for negative set phenomenon elimination

Resistive random-access memory (RRAM) is a promising non-volatile memory technology due to its fast operation, low power consumption, and high reliability. However, the negative set phenomenon remains a challenge for RRAM, which can lead to the deterioration of device switching parameters. In this study, we successfully addressed this issue by inserting a NiO blocking layer between the ZrO2 and Ag top electrodes in ZrO2-based RRAM. In addition, the resistive switching characteristics of the device are significantly enhanced by the incorporation of a p-type oxide NiO layer. Compared to single-layer ZrO2 devices, the double-layer Ag/NiO/ZrO2/ITO RRAM exhibits improved cycling durability (>500 cycles) and good retention time (3 × 104s). Our analysis of the device conduction mechanism and proposed resistive switching model suggest that oxygen vacancies play a connecting role in the reset process, leading to failed reset behavior. Through the incorporation of a p-type semiconductor NiO layer into ZrO2-based RRAMs, the interference of oxygen vacancies on the reset process can be effectively impeded. This approach not only provides an effective resolution to the unforeseen negative set phenomenon in RRAM devices, but it also holds paramount significance for the advancement of high-performance RRAMs.

Nature of point defects in monolayer MoS2 and the MoS2/Au(111) heterojunction

Deposition of MoS2 on Au(111) alters the electronic properties of MoS2. In this study, we investigate the free-standing MoS2 monolayer and the MoS2/Au(111) heterostructure, with and without strain, as well as defects of interest in memristive and neuromorphic applications. We focus on the so-called atomristor devices based on monolayer materials that achieve resistive switching characteristics with the adsorption and desorption of metal adatoms. Our study confirms that the formation of midgap states is the primary mechanism behind the resistive switching. Our results show that strain lowers the adsorption/desorption energies of Au+defect structures of interest, leading to more favorable switching energies, but simultaneously reduces the switching ratio between states of differing conductivities. The presence of the Au(111) substrate additionally introduces non-uniform amounts of strain and charge transfer to the MoS2 monolayer. We propose that the induced strain contributes to the experimentally observed n- to p-type transition and Ohmic to Schottky transition in the MoS2 monolayer. The charge transfer leads to a permanent polarization at the interface, which can be tuned by strain. Our study has important implications on the role of the electrode as being a source of the observed variability in memristive devices and as an additional degree of freedom for tuning the switching characteristics of the memristor device.

Study on multifunctional resistive switching and UV light detection characteristics in p-PEDOT:PSS/i-BFO/n-ZnO hybrid structures

The present research work based on the newly prepared organic-inorganic hybrid heterostructure will be exploited to develop a multifunctional device including non-volatile resistance switching memory devices, and ultraviolet (UV) light detection behavior for the first time based on p-PEDOT:PSS/i-BFO/n-ZnO junctions. Using a spray pyrolysis technique, n-type zinc oxide (ZnO) and i-type bismuth ferrite (BiFeO3) thin film layers were prepared on the clean glass substrates at temperature 673 K. Using a spin coater method, the p-PEDOT:PSS were grown upon a bismuth ferrite (BiFeO3) thin film with a constant spin velocity of 2000 rpm and heated at 363 K. The current (I)–voltage (V), photoresponse characteristics and resistive switching (RS) behavior of the fabricated p-PEDOT:PSS/i-BFO/n-ZnO hybrid devices were carried out. The device shows high photoresponsivity (R) of 0.001 285 A W−1 and fast photoresponse switching speed with the measured rise and fall time of 493 and 970 ms respectively. Based on the electrical properties, a conductive filament formation/rupture mechanism is proposed to explain the observed RS characteristics.

Nonvolatile resistive switching in interface-dominated memristors utilizing two-dimensional Cs2Pb(SCN)2Br2 perovskite films

In this study, all-inorganic two-dimensional (2D) perovskite Cs2Pb(SCN)2Br2 was employed in a thin-film vertical structure prototype memristor. The device consisted of a Cs2Pb(SCN)2Br2 film prepared through solution approach, sandwiched between an Ag electrode and a TiO2/FTO substrate bottom electrode. Two types of resistive switching (RS) behaviors were observed within a single device at different temperatures. At room temperature, the dominant control mechanism was the interface Schottky barrier, whereas at higher temperatures, the primary driving force shifted to the conductive channel. The device has an on/off ratio exceeding 103 under the interface control mechanism. The migration of mobile bromine vacancies within the Cs2Pb(SCN)2Br2 film, whose concentration was enhanced by the infiltration and reaction of the Ag active electrode within the Cs2Pb(SCN)2Br2 film, is proposed to be the root cause for both types of RS characteristics. These findings offer insights into the potential application of 2D Cs2Pb(SCN)2Br2 perovskite in RS memory devices.

High-performance memristor for energy-efficient artificial optoelectronic synapse based on BiVO4 nanosheets

Artificial optoelectronic synapses have drawn extensive attention owing to their ability to combine the optical and electrical responses. Those photosensitive materials that has been reported in memristors have the potential to be adopted in such optoelectronic synapses. Herein, optoelectronic synapses can be achieved based on two-terminal memristors by using two-dimensional (2D) BiVO4 with monoclinic scheelite (m-BiVO4) structure as the memristive layer. The fabricated memristors exhibit bipolar resistive switching (RS) characteristics with stable retention and reliable endurance performance. Furthermore, both electrical and optical synaptic functions can be achieved based on the memristors, such as long-term potentiation (LTP) and depression (LTD) stimulated by the voltages pulses as well as short-term and long-term memory under the light stimulation. More importantly, owing to the LTP and LTD functions with high symmetry, linearity and good repeatability of the LTP/LTD cycles, the artificial neural network can be simulated to achieve image recognition with a high accuracy for handwritten digits. Moreover, both the electrical and optical synapses can be used to emulate the “learning-forgetting” behaviors of human brain. Remarkably, the energy consumption per synaptic event in the optical and electrical modes can be calculated, indicating potential applications in energy-efficient synaptic devices. The m-BiVO4 nanosheets not only demonstrate good non-volatile RS behaviors but also implement energy-efficient optoelectronic synaptic functions, providing a promising strategy for applications in future neuromorphic computing.

Artificial Synapse Based on a δ-FAPbI3/Atomic-Layer-Deposited SnO2 Bilayer Memristor.

Halide perovskite-based resistive switching memory (memristor) has potential in an artificial synapse. However, an abrupt switch behavior observed for a formamidinium lead triiodide (FAPbI3)-based memristor is undesirable for an artificial synapse. Here, we report on the δ-FAPbI3/atomic-layer-deposited (ALD)-SnO2 bilayer memristor for gradual analogue resistive switching. In comparison to a single-layer δ-FAPbI3 memristor, the heterojunction δ-FAPbI3/ALD-SnO2 bilayer effectively reduces the current level in the high-resistance state. The analog resistive switching characteristics of δ-FAPbI3/ALD-SnO2 demonstrate exceptional linearity and potentiation/depression performance, resembling an artificial synapse for neuromorphic computing. The nonlinearity of long-term potentiation and long-term depression is notably decreased from 12.26 to 0.60 and from -8.79 to -3.47, respectively. Moreover, the δ-FAPbI3/ALD-SnO2 bilayer achieves a recognition rate of ≤94.04% based on the modified National Institute of Standards and Technology database (MNIST), establishing its potential in an efficient artificial synapse.

Formation-free resistive switching in nanocrystalline tellurium oxide

In this work, we report on the observation of resistive switching (RS) in the nanocrystalline tellurium oxide (TeO x ) in ITO/TeO x /Ag device configuration. The TeO x films grown in an O2/Ar environment have dominant β-TeO2 along with other polymorphs and amorphous TeO2. From the RS characteristics, it is suggestive that the β-TeO2 phase promotes the conductive filament formation across the highly insulating amorphous matrix. The memory device demonstrates bipolar RS with excellent endurance, retention and on–off ratio. The device also features formation-free switching with low set and reset voltage (0.6 V and −0.8 V respectively) and displays multilevel switching upon varying compliance current. Current-Voltage characterization clarifies the conduction path is indeed filamentary type. The result highlights that TeO x can be a prominent RS material for memory and brain-inspired computing devices.

Vacancy-Engineered Nickel Ferrite Forming-Free Low-Voltage Resistive Switches for Neuromorphic Circuits.

Innovations in resistive switching devices constitute a core objective for the development of ultralow-power computing devices. Forming-free resistive switching is a type of resistive switching that eliminates the need for an initial high voltage for the formation of conductive filaments and offers promising opportunities to overcome the limitations of traditional resistive switching devices. Here, we demonstrate mixed charge state oxygen vacancy-engineered electroforming-free resistive switching in NiFe2O4 (NFO) thin films, fabricated as asymmetric Ti/NFO/Pt heterostructures, for the first time. Using pulsed laser deposition in a controlled oxygen atmosphere, we tune the oxygen vacancies together with the cationic valence state in the nickel ferrite phase, with the latter directly affecting the charge state of the oxygen vacancies. The structural integrity and chemical composition of the films are confirmed by X-ray diffraction and hard X-ray photoelectron spectroscopy, respectively. Electrical transport studies reveal that resistive switching characteristics in the films can be significantly altered by tuning the amount and charge state of the oxygen vacancy concentration during the deposition of the films. The resistive switching mechanism is seen to depend upon the migration of both singly and doubly charged oxygen vacancies formed as a result of changes in the nickel valence state and the consequent formation/rupture of conducting filaments in the switching layer. This is supported by the existence of an optimum oxygen vacancy concentration for efficient low-voltage resistive switching, below or above which the switching process is inhibited. Along with the filamentary switching mechanism, the Ti top electrode also enhances the resistive switching performance due to interfacial effects. Time-resolved measurements on the devices display both long- and short-term potentiation in the optimized vacancy-engineered NFO resistive switches, ideal for solid-state synapses achieved in a single system. Our work on correlated oxide forming-free resistive switches holds significant potential for CMOS-compatible low-power, nonvolatile resistive memory and neuromorphic circuits.

Exploring bipolar resistive switching behavior of sprayed BaTiO3 thin films for nonvolatile memory application

The memristive properties of barium titanate (BT) thin films deposited by cost-effective spray pyrolysis technique are explored. The device was configured as Ag/BT/FTO. The electrical measurements unveiled robust bipolar resistive switching (BRS) characteristics in the devices with memory window ∼35. This behavior, attributed to intrinsic defects within BaTiO3, demonstrated the potential of these films for applications in advanced electronic devices like Resistive-Random Access Memory (RRAM). The observed phenomenon arises from the generation of polarized areas within the material, responsive to an applied electric field. Specifically focusing on the memristive aspects, this study indicated promising non-volatile memory performance. All devices undergo the SET process between 0.9 and 1.7 V, and the RESET process takes place between −1.3 to −1.9 V. According to the statistical distribution of SET and RESET voltages, the coefficient of variation (CV) for all devices is less than 18 %. The Ag/BT/FTO memristive device exhibited endurance through 103 cycles of switching, attesting to its reliability. Moreover, the device displayed the capability to maintain stored data for 104 seconds. This establishes the suitability of spray-deposited BaTiO3 thin films for memory-based applications.

Low voltage resistance switching characteristics of Cu/MoS2/Cu/ITO devices

The resistive switching behavior is observed in the Cu/MoS2/Cu/ITO structures, which has been deposited by magnetron sputtering. With the increase in MoS2 thickness, the resistive switching behavior is gradually weakened. The optimal device with a MoS2 thickness of 120[Formula: see text]nm has a lower Set voltage and Reset voltage, where Set voltage is 0.14–0.3[Formula: see text]V and Reset voltage is −0.24[Formula: see text]V to −0.08[Formula: see text]V. The device also has a resistive switching ratio of up to 105 high resistance state/low resistance state, a data retention time over 104[Formula: see text]s, and can endure more than 103 cycles. As the limiting current increases, the resistance switching (RS) characteristics of devices with MoS2 thickness of 200[Formula: see text]nm at both positive and negative biases are improved. There is no RS behavior in ITO/MoS2/ITO devices fabricated by the same method, which indicates that sulfur vacancies have little effect on the RS characteristics of Cu/MoS2/Cu/ITO devices. Moreover, since the migration barrier and diffusion activation energy of Cu in MoS2 are lower than those of sulfur vacancy, combined with the data fitting structure, it is shown that the RS behavior is formed because Cu ions control the connectivity and fracture of conductive filaments through the diffusion and migration of MoS2 layer.

Resistive switching memory using buckybowl sumanene-inserted bilayer graphene

The bowl-shaped molecules of the nanocarbon material called sumanene have structural flexibility (bowl inversion). In the case of the sumanene molecule used as an intercalant between graphene layers, it has been predicted that holes and electrons are unevenly distributed according to the bowl inversion. Using the property of sumanene molecules, we expected that resistive switching for the nonvolatile memory applications could be achieved by the sumanene-inserted bilayer graphene. In this study, metal–insulator–metal devices with sumanene-inserted bilayer graphene are fabricated. As a result, it is observed that the resistance of the sumanene-inserted bilayer graphene changes by applying voltage, demonstrating resistive switching characteristics. This result implies the possibility of realizing a novel ultra-thin resistive memory device using nanocarbon technologies.

Long‐ and Short‐Term Memory Characteristics Controlled by Electrical and Optical Stimulations in InZnO‐Based Synaptic Device for Reservoir Computing

AbstractIn this study, the resistive switching phenomenon and synaptic mimicry characteristics of an indium tin oxide (ITO)/indium zinc oxide (IZO)/Al2O3/TaN device are characterized. The insertion of a thin Al2O3 layer via atomic layer deposition improves the resistive switching characteristics such as cycle‐to‐cycle and device‐to‐device uniformity and reduces the power consumption of the proposed device with respect to a single‐layer ITO/IZO/TaN device. The proposed device exhibits the coexistence of volatile and nonvolatile characteristics under optical and electrical measurement conditions. Nonvolatile memory characteristics with stable retention results are used for synaptic applications by emulating potentiation, depression, and spike‐timing‐dependent plasticity. Furthermore, the device shows volatile characteristics under ultraviolet‐light illumination, emulating paired‐pulse facilitation and excitatory post‐synaptic current responses. Finally, optical‐enhanced reservoir computing is implemented based on the nonlinear and volatile nature of the IZO‐based resistive random‐access memory device.

CogniFiber: Harnessing Biocompatible and Biodegradable 1D Collagen Nanofibers for Sustainable Nonvolatile Memory and Synaptic Learning Applications.

Here, resistive switching (RS) devices are fabricated using naturally abundant, nontoxic, biocompatible, and biodegradable biomaterials. For this purpose, 1D chitosan nanofibers (NFs), collagen NFs, and chitosan-collagen NFs are synthesized by using an electrospinning technique. Among different NFs, the collagen-NFs-based device shows promising RS characteristics. In particular, the optimized Ag/collagen NFs/fluorine-doped tin oxide RS device shows a voltage-tunable analog memory behavior and good nonvolatile memory properties. Moreover, it can also mimic various biological synaptic learning properties and can be used for pattern classification applications with the help of the spiking neural network. The time series analysis technique is employed to model and predict the switching variations of the RS device. Moreover, the collagen NFs have shown good cytotoxicity and anticancer properties, suggesting excellent biocompatibility as a switching layer. The biocompatibility of collagen NFs is explored with the help of NRK-52E (Normal Rat Kidney cell line) and MCF-7 (Michigan Cancer Foundation-7 cancer cell line). Additionally, the biodegradability of the device is evaluated through a physical transient test. This work provides a vital step toward developing a biocompatible and biodegradable switching material for sustainable nonvolatile memory and neuromorphic computing applications.

Study on the Sodium-Doped Titania Interface-Type Memristor.

Memristors integrated into a crossbar-array architecture (CAA) are promising candidates for analog in-memory computing accelerators. However, the relatively low reliability of the memristor device and sneak current issues in CAA remain the main obstacles. Alkali ion-based interface-type memristors are promising solutions for implementing highly reliable memristor devices and neuromorphic hardware. This interface-type device benefits from self-rectifying and forming-free resistive switching (RS), and exhibits relatively low variation from device to device and cycle to cycle. In a previous report, we introduced an in situ grown Na/TiO2 memristor using atomic layer deposition (ALD) and proposed a RS mechanism from experimentally measured Schottky barrier modulation. Self-rectifying RS characteristics were observed by the asymmetric distribution of Na dopants and oxygen vacancies as the Ti metal used as the adhesion layer for the bottom electrode diffuses over the Pt electrode at 250 °C during the ALD process and is doped into the TiO2 layer. Here, we theoretically verify the modulation of the Schottky barrier at the TiO2/Pt electrode interface by Na ions. This study fabricated a Pt/Na/TiO2/Pt memristor device and confirmed its self-rectifying RS characteristics and stable retention characteristics for 24 h at 85 °C. Additionally, this device exhibited relative standard deviations of 27 and 7% in the high and low resistance states, respectively, in terms of cycle-to-cycle variation. To verify the RS mechanism, we conducted density functional theory simulations to analyze the impact of Na cations at interstitial sites on the Schottky barrier. Our findings can contribute to both fundamental understanding and the design of high-performance memristor devices for neuromorphic computing.

Stacked structure dependence on resistive switching characteristics in sumanene molecular memory

Nonvolatile memories using molecule (molecule memories) are attracting attention. This is because these materials are suitable for miniaturization and higher capacity of memories in terms of their properties and dimensions. We have already demonstrated that the metal–insulator–metal (MIM) devices with sumanene-inserted bilayer graphene show huge resistive switching characteristics. However, the reason why resistive switching occurs in the graphene/sumanene/graphene structure has yet to be clarified. In this work, to investigate the mechanisms of the resistive switching phenomenon in sumanene-inserted bilayer graphene, plural kinds of stacked MIM structures are fabricated and evaluated. As a result, the measurement results clearly show that the graphene/sumanene/graphene structure is indispensable in the resistive switching phenomenon. Furthermore, based on the temperature dependence of the resistive switching, it is confirmed that a significant I ON/I OFF ratio can be obtained at higher operation temperatures.

Effect of Electrochemically Active Top Electrode Materials on Nanoionic Conductive Bridge Y2O3 Random-Access Memory.

Herein, sol-gel-processed Y2O3 resistive random-access memory (RRAM) devices were fabricated. The top electrodes (TEs), such as Ag or Cu, affect the electrical characteristics of the Y2O3 RRAM devices. The oxidation process, mobile ion migration speed, and reduction process all impact the conductive filament formation of the indium-tin-oxide (ITO)/Y2O3/Ag and ITO/Y2O3/Cu RRAM devices. Between Ag and Cu, Cu can easily be oxidized due to its standard redox potential values. However, the conductive filament is easily formed using Ag TEs. After triggering the oxidation process, the formed Ag mobile metal ions can migrate faster inside Y2O3 active channel materials when compared to the formed Cu mobile metal ions. The fast migration inside the Y2O3 active channel materials successfully reduces the SET voltage and improves the number of programming-erasing cycles, i.e., endurance, which is one of the nonvolatile memory parameters. These results elucidate the importance of the electrochemical properties of TEs, providing a deeper understanding of how these factors influence the resistive switching characteristics of metal oxide-based atomic switches and conductive-metal-bridge-filament-based cells.

Artificial Tactile Sensing Neuron with Tactile Sensing Ability Based on a Chitosan Memristor.

Owing to the highly parallel network structure of the biological neural network and its triggered processing mode, tactile sensory neurons can realize the perception of external signals and the functions of perception, memory, and data processing by adjusting the synaptic weight. In this paper, a piezoresistive pressure sensor is combined with a memristor to design an artificial tactile sensory neuron. The polyurethane sponge sensor has excellent sensitivity and can convert physical stimuli into electrical signals, and the chitosan-based memristor has stable bipolar resistive switching characteristics, allowing further information to be memorized and processed. The neuron can respond to tactile stimuli of different degrees, durations, and frequencies; realize potentiation/depression modulation, paired-pulse facilitation, and spike-timing-dependent plasticity; exhibit spike-rate-dependent plasticity; and store and erase tactile information through memistor state switching, which has great application potential in biological sensing systems.

Improved resistive switching characteristics of solution processed ZrO2/SnO2 bilayer RRAM via oxygen vacancy differential

In this study, a solution-processed bilayer structure ZrO2/SnO2 resistive switching (RS) random access memory (RRAM) is presented for the first time. The precursors of SnO2 and ZrO2 are Tin(Ⅱ) acetylacetonate (Sn(AcAc)2) and zirconium acetylacetonate (Zr(C5H7O2)4), respectively. The top electrode was deposited with Ti using an E-beam evaporator, and the bottom electrode used an indium–tin–oxide glass wafer. We created three devices: SnO2 single-layer, ZrO2 single-layer, and ZrO2/SnO2 bilayer devices, to compare RS characteristics such as the I–V curve and endurance properties. The SnO2 and ZrO2 single-layer devices showed on/off ratios of approximately 2 and 51, respectively, along with endurance switching cycles exceeding 50 and 100 DC cycles. The bilayer device attained stable RS characteristics over 120 DC endurance switching cycles and increased on/off ratio ∼2.97 × 102. Additionally, the ZrO2/SnO2 bilayer bipolar switching mechanism was explained by considering the Gibbs free energy (ΔG o) difference in the ZrO2 and SnO2 layers, where the formation and rupture of conductive filaments were caused by oxygen vacancies. The disparity in the concentration of oxygen vacancies, as indicated by the Gibbs free energy difference between ZrO2 (ΔG o = −1100 kJ mol−1) and SnO2 (ΔG o = −842.91 kJ mol−1) implied that ZrO2 exhibited a higher abundance of oxygen vacancies compared to SnO2, resulting in improved endurance and on/off ratio. X-ray photoelectron spectroscopy analyzed oxygen vacancies in ZrO2 and SnO2 thin films. The resistance switching characteristics were improved due to the bilayer structure, which combines a higher oxygen vacancy concentration in one layer with a lower oxygen vacancy concentration in the switching layer. This configuration reduces the escape of oxygen vacancies to the electrode during RS.