Bipolar Resistive Switching Properties Research Articles

Forming-less flexible memristor crossbar array for neuromorphic computing applications produced using low-temperature atomic layer deposition

The rapid development of wearable artificial intelligence devices based on memristor crossbar arrays has increased the demand for flexible electronics. However, fabricating crossbar arrays on flexible substrates faces inherent challenges, notably due to the complex fabrication process at low temperatures. Moreover, ensuring the stability and reliability of memristor device remains a crucial issue. To address these issues, this study introduced N-doped TaOx (N:TaOx) as a flexible memristor crossbar array fabricated via atomic layer deposition directly on a flexible substrate at an exceptionally low temperature (150 °C). The flexible PET/ITO/N:TaOx/TiN memristor device exhibited forming-less bipolar resistive switching properties with analog memory characteristics. This was accomplished by increasing the nitrogen doping concentration and effectively reducing oxygen-related defects in TaOx. The amorphous-phase flexible N:TaOx memristor demonstrated remarkable stability, enduring 500 switching cycles and retaining its state for 24 h during bending tests involving 104 bending cycles at 2.5 mm bending radius. Furthermore, a 6 × 6 flexible memristor crossbar array was fabricated successfully, with all 36 devices exhibiting well-defined memristor behavior and minimal variation attributed to the film's uniformity achieved through ALD process. Additionally, by programming the tunable conductance of each device in the array, characters of desired shapes can be formed and read. Regarding their synaptic behavior via long-term potentiation and depression, the proposed flexible memristor device showed an outstanding accuracy of 96.44 % in image recognition tasks under extreme bending conditions, employing the MNIST and Fashion-MNIST datasets. The N:TaOx memristor deposited at low temperatures thus exhibits significant potential for use in wearable neuromorphic hardware applications due to its high density, high performance, reliability, and precise image recognition.

Resistive switching behaviour of nickel nanoparticle-embedded naphthalene sulphonic acid-doped polyaniline nanocomposites

Hybrid nanocomposite (NC) materials comprising organic polymers and inorganic metal nanoparticles (NPs) with unique properties are popular for their advanced technological applications including resistive switching memory devices. Herein, NCs of 2-naphthalene sulphonic acid-doped polyaniline nanotubes (PANI-NSA NTs) and nickel nanoparticles (Ni NPs) were synthesized via a facile chemical synthesis procedure where metallic Ni NPs were embedded in/deposited onto the surface of PANI-NSA NTs by a simple reduction method. Different characterization methods revealed successful deposition of weak ferromagnetic Ni NPs onto the PANI-NSA matrix. The bipolar resistive switching behaviour of the as-synthesized PANI-NSA + Ni NCs was investigated under the application of voltage stress in a two-terminal sandwiched device configuration. The fabricated indium tin oxide/PANI-NSA + Ni/silver (ITO/PANI-NSA + Ni/Ag) device displays bipolar resistive switching properties having a memory window of ∼1.5 × 103, and switches effectively over 200 cycles. Ohmic conduction in the lower-voltage regime and the space-charge-limited Mott–Gurney current conduction model in the higher-voltage region were identified as major charge conduction mechanisms in the high resistive state of the device. On the other hand, in the entire low resistive state region the experimental data followed the Mott–Gurney conduction model.

Double-Forming Mechanism of TaOx-Based Resistive Memory Device and Its Synaptic Applications.

The bipolar resistive switching properties of Pt/TaOx/InOx/ITO-resistive random-access memory devices under DC and pulse measurement conditions are explored in this work. Transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the structure and chemical compositions of the devices. A unique two-step forming process referred to as the double-forming phenomenon and self-compliance characteristics are demonstrated under a DC sweep. A model based on oxygen vacancy migration is proposed to explain its conduction mechanism. Varying reset voltages and compliance currents were applied to evaluate multilevel cell characteristics. Furthermore, pulses were applied to the devices to demonstrate the neuromorphic system's application via testing potentiation, depression, spike-timing-dependent plasticity, and spike-rate-dependent plasticity.

Implementation of Highly Stable Memristive Characteristics in an Organic–Inorganic Hybrid Resistive Switching Layer of Chitosan-Titanium Oxide with Microwave-Assisted Oxidation

This study proposes a high-performance organic–inorganic hybrid memristor for the development of neuromorphic devices in the memristor-based artificial synapse. The memristor consists of a solid polymer electrolyte (SPE) chitosan layer and a titanium oxide (TiOx) layer grown with a low-thermal-budget, microwave-assisted oxidation. The fabricated Ti/SPE–chitosan/TiOx/Pt-structured memristor exhibited steady bipolar resistive switching (BRS) characteristics and demonstrated excellent endurance in 100-cycle repetition tests. Compared to SPE–chitosan memristors without a TiOx layer, the proposed organic–inorganic hybrid memristor demonstrated a higher dynamic range and a higher response to pre-synaptic stimuli such as short-term plasticity via paired-pulse facilitation. The effect of adding the TiOx layer on the BRS properties was examined, and the results showed that the TiOx layer improved the chemical and electrical superiority of the proposed memristor synaptic device. The proposed SPE–chitosan organic–inorganic hybrid memristor also exhibited a stable spike-timing-dependent plasticity, which closely mimics long-term plasticity. The potentiation and depression behaviors that modulate synaptic weights operated stably via repeated spike cycle tests. Therefore, the proposed SPE–chitosan organic–inorganic hybrid memristor is a promising candidate for the development of neuromorphic devices in memristor-based artificial synapses owing to its excellent stability, high dynamic range, and superior response to pre-synaptic stimuli.

Resistive switching of carbon nitride supported ultra-fine lead sulfide based device: Implementation of a 8-bit memristor

Resistive switching refers to a physical phenomenon where dielectric materials suddenly change their resistance under the action of an electric field. Here, a high temperature in-situ route was implemented to synthesis of lead sulfide nanoparticles, embedded on the carbon nitride matrix, CNLS, that exhibited bipolar resistive switching (BRS) property. The electron transport property of the device, made with the hybrid system (CNLS), was explained by Poole-Frenkel (PF) emission and Ohmic mechanism for the low conductance state (LCS) and high conductance state (HCS), respectively. The stability and nonvolatile performance of the low and high conductance states were examined and the device showed an average ON-OFF ratio in the order of 4 × 105. The Write-Read (1)-Erase-Read (0) cycle revealed a moderately good resolution between 2-Read operations (R0 & R1) for the CNLS based device. A 8-bit memory device made with the title material that successfully stored, process and recovered the binary information.

Dielectric and bipolar resistive switching properties of Ag doped As–S–Se chalcogenide for non-volatile memory applications

In this study, dielectric and bipolar resistive switching properties of the chalcogenide from the Ag–As40S30Se30 system were investigated for potential application in non-volatile memory devices. Preparation of the glasses was done with the use of melt-quenching technique. Current–voltage (I–V) characteristics were determined at different temperatures, and stability of the Ag/chalcogenide sample/Ag structure through constant value of memory window was noticed. Namely, it was observed that a bipolar resistive switching effect is present in the prepared samples with noticeable transitions between high-resistance and low-resistance states when the voltage polarity was changed. Temperature dependent I–V measurements indicated that resistive switching voltage decreases as temperature increases suggesting thermally activated motion of charge carriers. The conduction model fitting results suggested that the Ohmic and space-charge limited current conduction are responsible for resistive switch. Based on the analysis of the obtained results, resistive switching mechanism was explained by using filamentary conduction. In addition, study of dielectrical properties indicated presence of space charge polarization. The presented results show that the synthesized material has properties that suggest them for potential application in non-volatile memory devices.

Zn2SnO4 Thin Film Based Nonvolatile Positive Optoelectronic Memory for Neuromorphic Computing

An optoelectronic synaptic device based on the ITO/Zn2SnO4(ZTO)/ITO structure is fabricated which integrates the electronic memory and optical sensing properties along with synaptic functions. The fabricated device shows over 80% optical transparency for the entire visible region (400–800 nm). Post-oxide annealing treatment is performed in a nitrogen environment at 200 °C. Significant improvements in bipolar resistive switching properties of the device with low SET voltage (+0.93 V) and long DC endurance cycles (∼12000) are observed in the annealed device. The linearity of such memristive synapse is improved for 350 training epochs with a total number of 175000 pulses. The spike time dependent plasticity learning rule for the annealed device is demonstrated through the electric field. The optical sensing capabilities of this device including photonic potentiation (responsivity: 0.52 μA/W), photonic paired pulse facilitation by adjusting time interval between two identical light pulses, learning experience behavior, and multilevel memory feature by the repetition of optical pulse for ∼103 s are demonstrated under the blue light (wavelength “λ” = 405 nm) illumination at 50 mW/cm2. Photonic potentiation and electric depression behavior of the device mimic its nonvolatile synaptic plasticity. The linear fitting of I–V curve illustrates the dominance of Schottky emission and Poole–Frenkel conduction mechanisms at high and low resistance states, respectively. The electric response of the device is explained by the oxygen vacancy based filamentary model. The trapping and detrapping of electrons during the adsorption and desorption processes of atmospheric oxygen molecules on the ITO surface are responsible for the photoconduction phenomenon. To train the Hopfield neural network (HNN) model for image processing of 28 × 28 pixels, the normalized experimental data of long-term potentiation/depression are employed to mimic the learning behavior of the human brain. The convergence of electronic data storage and optical sensor has high potential which provides a path toward the future smart invisible optoelectronics for artificial intelligence.

Bipolar resistive switching properties of TiO x /graphene oxide doped PVP based bilayer ReRAM

In this paper, firstly, some recently explored promising materials and processes for resistive random access memory (ReRAM) devices with bipolar switching mechanism along with their performance are discussed. Further, resistive switching behaviour of TiO x /graphene oxide (GO):poly(4-vinylphenol) (PVP) based bilayer in ReRAM devices is demonstrated. It was found that bipolar resistive switching behaviour is significantly enhanced by embedding 2D material such as GO in the organic polymer acting as switching layer. ReRAM devices with Ag/PVP:GO/TiO x /fluorine doped tin oxide (FTO) structure exhibited high ON/OFF current ratio (>103), low voltage operation, and high retention time. Bipolar resistive switching from these engineered active layers will have great potential for future large area and sustainable electronics.

Tunable multiferroic and forming-free bipolar resistive switching properties in multifunctional BiFeO3 film by doping engineering

The advent of multiferroic-based materials has opened the plethora for high tunable multifunctional materials and ultra-fast operation for future non-volatile memory technology. Multifunctional rhombohedral Bi0.94Y0.06Fe0.95Mn0.05O3 (BYFMO) film is grown on fluorine-doped tin oxide to investigate the electromechanical and resistive switching properties in Ag/BYFMO/FTO RRAM configuration. UV–visible absorbance spectra reveal the semiconducting behavior of BYFMO, and the band-gap is found to be 2.37 eV. The magnetic hysteresis curve manifests the soft ferromagnetic nature by suppressing the spiral spin modulated structure, supported by MFM imaging. The Y-Mn co-doped BFO possesses highly tunable piezoelectric and ferroelectric features with maximum domains preferred along 710 and 1090. Lateral domain growth is observed with the increase in tip bias voltage. The Ag/BYFMO/FTO RRAM shows distinct bipolar resistive switching behavior at the SET (ON), and RESET (OFF) processes are obtained at voltage VSET = +1.7V and VRESET = −2.8V, respectively. The memory window (ON/OFF) between high resistance state and low resistance state is about ~ 100, which can be sustained up to 100 testing cycles and 103s without any degradation, indicating that the BYFMO based device exhibits better endurance and retention properties. Moreover, the resistive switching mechanism of the device can be well explained by space charge limited current conduction, which is well supported by conducting a filamentary model. With excellent piezoelectric and resistive switching performance, the multifunctional BYFMO has enough potential for future non-volatile memory technology.

Bipolar resistive switching and memristive properties of sprayed deposited Bi2WO6 thin films

The present work demonstrates the development and investigation of bipolar resistive switching characteristics of the Al/Bi2WO6/FTO thin-film memristive device. The Bi2WO6 (BWO) active layer was deposited on FTO coated glass substrates using a spray pyrolysis technique and the effect of spray volume on resistive switching characteristics was investigated. X-ray diffraction analysis reveals that the thin films were polycrystalline with the orthorhombic crystal structure. The spherical grains were observed from the morphological study for an optimized sample and incomplete growth of grains was seen for other samples. The energy dispersive X-ray spectra show the presence of different constituent elements such as Bi, W, and O. The pinched hysteresis loop is the basic signature of a memristive device and was observed in all Al/BWO/FTO devices. The bipolar resistive switching characteristic was observed in all devices. The optimized device shows maximum current and the highest memristive area. Endurance test suggests that the device can be switched in consecutive 2 × 103 switching cycles and can retain the data up to 103 s without any observable degradation in the switching properties. The Al/BWO/FTO device possesses the double valued charge-flux property, suggesting the presence of memristive properties. The HRS follows the Schottky conduction mechanism while LRS govern by the Ohmic charge transport mechanism.

Resistive switching properties and conduction mechanisms of LaSmOx thin film by RF sputtering for RRAM applications

Polycrystalline LaSmOx (LSO) thin films were prepared by using RF sputtering and the bipolar resistive switching (BRS) properties in the Al/LSO/ITO structure were investigated. The impact of Ar/O2 ratio, film thickness and post metal annealing (PMA) condition on the resistive switching (RS) properties were also studied. The conductive mechanism is mainly dominated by the numbers of oxygen vacancies, which can be controlled through a different deposition atmosphere (Ar/O2) ratio and film thickness. In addition, the resistive switching characteristics can be improved by post metal annealing treatment due to film densification and the formation of AlOx interface layer in between the top electrode and the LaSmOx thin film. The optimized RRAM device revealed a profound improvement in the switching cycles, which can be as high as 4580.

Forming-free and multilevel resistive switching properties of hydrothermally synthesized hexagonal molybdenum oxide microrods

In recent years, resistive switching memory devices are attracted much attention for high-density non-volatile memory applications owing to their cell scalability, multilevel operations, and 3D capability in crossbar memory arrays. In this work, we report the forming-free and multilevel resistive switching properties of hydrothermally synthesized hexagonal molybdenum oxide (h-MoO3) microrods. The formation of h-MoO3 microrods was confirmed by using the X-ray diffraction technique and scanning electron microscopy. Different chemical properties of h-MoO3 microrods were determined by energy-dispersive X-ray, photoluminescence, Raman, and X-ray photoelectron spectroscopic techniques. The memory device was fabricated in a Ti/MoO3/FTO structure and its bipolar resistive switching properties were investigated. The memory device shows voltage-dependent tunable I-V properties and shows electroforming-free operation. Moreover, we have calculated the different memristive properties and showed that the device possesses double-valued charge-magnetic flux characteristics, suggesting the dominance of memristive properties in the Ti/MoO3/FTO device. We further explored the multilevel resistive switching property of the device by varying the RESET voltage. The Ti/MoO3/FTO memristive device can able to show four distinct resistive states during endurance and retention tests. The statistical analysis suggested that the device has less variation during the cycle-to-cycle operation. The device conduction mechanism was obtained by fitting different charge transport models, and a possible resistive switching mechanism is presented based on the observed multilevel resistive switching effect of the Ti/MoO3/FTO memristive device.

Bipolar resistive switching and non-volatile memory properties of MnO2-polyaniline (PANI) nanocomposite

Organic materials are becoming a promising candidate for non-volatile memory especially resistive switching memories. The present work reports bipolar resistive switching and memristive properties of polyaniline coated MnO2 nanocomposite. The hybrid nanocomposite was synthesized by oxidative polymerization of aniline in the presence of the MnO2 nanostructures. The XRD analysis confirms the α-MnO2 phase and the TEM micrograph reveals the formation of nanorods of the material. The results of Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) and Thermogravimetric analysis (TGA) confirmed the presence of the polymer in the composite. The developed device shows bipolar resistive switching behavior with a memory window ~7 × 102, switches efficiently over 103 cycles, and can retain the data over 104 seconds. Space charge limited current conduction model along with the possible filamentary route of operation describes conduction and resistive switching mechanisms of the device.

Annealed AlOx film with enhanced performance for bipolar resistive switching memory

Although some efforts have been dedicated to explore aluminum oxide (AlOx) based memory devices in the past few years, the disappointed stability and complicated fabrication process strictly limit its wide applications. In this study, we introduce the annealing treatment as an effective method to substantially improve the non-volatile resistive switching performance of AlOx film based resistive memory devices. Fabricated by radio frequency magnetron sputtering method at room temperature, the AlOx resistive memory devices are subsequently annealed in nitrogen atmosphere with the temperature range from 100 °C to 500 °C. The devices exhibit enhanced bipolar resistive switching properties with forming-free nature, high HRS/LRS ratio (>103), long retention time (>104s) and statistical switching performance (>200 cycles). The conductive filaments constructed by oxygen vacancies has been demonstrated as a dominant factor for the resistive switching behavior in the AlOx film based memory devices, and introducing oxygen-free atmosphere annealing treatment will increase the proportion of oxygen vacancies, thus resulting in a considerable resistive switching improvement. Our work proves the great potential of annealed AlOx film as resistive switching layer in resistive random access memory devices, and also paves the way for optimization of relevant devices based on binary metal oxides.

Bipolar resistive switching properties of titanium dioxide thin films deposited by different techniques

A comparative study of bipolar resistive switching in thin films of titanium dioxide, fabricated by different techniques, was carried out by analysis of current-voltage characteristics (I-V). For this purpose metal-insulator-metal (MIM) structures were formed with 60-nm-thick titanium dioxide layer deposited by atomic layer deposition (ALD) or RF magnetron sputtering. Based on the analysis of resistance switching characteristics, it was found that the deposition technique of titanium dioxide thin films influences the reproducibility of high-resistance state (HRS) at cycling measurements, the on-resistance (low resistance state)/off-resistance (HRS) ratio, the average values of SET [switching the resistance from a HRS to a low resistance state (LRS)] and RESET [switching the resistance from LRS to HRS] voltages and the number of resistive switching cycles. The results of study of the thin film topography performed by atomic force microscopy (AFM) suggest that the difference in resistive switching parameters could be caused by structural properties of titanium dioxide layers deposited by different techniques.

VLS growth of pure and Au decorated β-Ga2O3 nanowires for room temperature CO gas sensor and resistive memory applications

High-density single crystalline β-Ga2O3 nanowires on silicon (1 0 0) substrates were grown by vapour-liquid-solid growth method. We have characterized the pure β-Ga2O3 nanowires along with the Au-decorated β-Ga2O3 nanowires. The CO gas sensors at room temperature (RT) have been studied for pure and Au decorated nanowires with multiple-networked array and single nanowire devices. The diameter of the 1D nanostructure ranged from 127 ± 5 nm. The synthesized nanowires were studied using Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), Energy Dispersive X-ray Spectroscopy (EDS), Gracing Incidence X-ray Diffraction (GI-XRD), Photoluminescence (PL), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Using the Focussed Ion Beam (FIB) technique, single nanowire gas sensor devices were fabricated. Single nanowire RT CO gas sensors using the proposed Au decorated β-Ga2O3 nanowire achieved remarkable sensitivity for 100 ppm CO gas at room temperature. Besides, we have compared the RT CO gas sensing properties of multiple-networked Au decorated β-Ga2O3 nanowires with single Au-decorated β-Ga2O3 nanowire and single pure β-Ga2O3 nanowire. In addition, bipolar resistive switching property is inspected for the Au/pure β-Ga2O3 nanowires/p-Si and Au/Au decorated β-Ga2O3 nanowires/p-Si structures.

Negative differential resistance effect and dual bipolar resistive switching properties in a transparent Ce-based devices with opposite forming polarity

In this work, we have fabricated a transparent Ce-based device with aluminum-zinc oxide (AZO) as semiconducting electrode by radio-frequency (RF) sputtering on a transparent ITO/glass substrate at room temperature (RT). The device transmittance in the visible region of 400 to 800 nm was measured to be ~92%. Studies on the AZO/CeO2/ITO/glass device reveal a dual-mode bipolar resistive switching (RS) behavior. Transparent device is found to exhibit both positive-set/negative-reset and negative-set/positive-reset switching modes with very good repetitiveness in cycle-to-cycle (C2C) switching, excellent DC endurance (>103 cycles) and long retention (>104 s). In addition, negative differential resistance (NDR) was noted to arise during positive electroforming and set-processes, and its physical origin was explored. The physics behind the NDR and dual bipolar RS behaviors were explained by the rise and fall in the density of oxygen vacancies in the CeO2 layer, as was analyzed via x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) techniques. We believe that Ce-based transparent device presented in this work can offer robust passivation for electronic devices.

Bipolar-resistive switching and memristive properties of solution-processable cobalt oxide nanoparticles

This work reports the memristive properties of solution-processable cobalt oxide nanoparticles (CoO NPs) for resistive memory application. The memristive current???voltage hysteresis loop with good bipolar-resistive switching (BRS) property was shown by the developed device. Substantiate to this, the asymmetric device charge and double-valued charge???magnetic flux characteristics were calculated from the experimental electrical data and demonstrated the existence of the non-ideal memristor properties. The CoO memristive device can switch up to 103 BRS cycles and can retain the data up to 5????????103 s. The switching uniformity of the CoO memory device was elucidated by a cumulative probability distribution and statistical calculations. The low-resistance state shows little variation whereas broad variation was observed for high-resistance state. The theoretical model fitting results suggested that the conduction in the device during high-resistance sate was due to the Schottky and space charge-limited current and Ohmic current dominated in the low-resistance state. The formation and rupture of conductive filament with the assistance of interfacial dynamic is a possible reason for BRS in the CoO NPs-based memristive device.

Layered (C6H5CH2NH3)2CuBr4 Perovskite for Multilevel Storage Resistive Switching Memory

AbstractAlthough there have been attempts to use non‐lead based halide perovskite materials as insulating layers for resistive switching memory, the ratio of low resistance state (LRS) to high resistance state (HRS) ( = ON/OFF ratio) and/or endurance is reported to be mostly lower than 103. Resistive switching memory characteristics of layered (BzA)2CuBr4 (BzA = C6H5CH2NH3) perovskite with high ON/OFF ratio and long endurance are reported here. The X‐ray diffraction (XRD) pattern of the deposited (BzA)2CuBr4 layer shows highly oriented (00l) planes perpendicular to a Pt substrate. An Ag/PMMA/(BzA)2CuBr4/Pt device shows bipolar switching behavior. A forming step at around +0.5 V is observed before the repeated bipolar switching at the SET voltage of +0.2 V and RESET voltage of ‐0.3 V. The ON/OFF ratio as high as =108 is monitored along with an endurance of ≈2000 cycles and retention time over 1000 s. The high ON/OFF ratio enables multilevel storage characteristics as confirmed by changing the compliance currents. Ohmic conduction at the LRS and Schottky emission at HRS are involved in electrochemical metallization process. The bipolar resistive switching property is retained after storing the device at ambient condition under relative humidity of about 50% for 2 weeks, which indicates that (BzA)2CuBr4 is stable memory material.

Bipolar resistive switching property of Si3N4−xthin films depending on N deficiency

This study investigates a bipolar resistive switching property of a silicon nitride thin film deposited by plasma enhanced chemical vapor deposition using the SiH4and NH3as the Si- and N-sources, respectively.