Nonvolatile Resistive Switching Behavior Research Articles

Sol-Gel Derived ZnO Thin Films with Nonvolatile Resistive Switching Behavior for Future Memory Applications

Herein we report on a facile sol-gel spin-coating technique to fabricate ZnO thin films that grow preferentially along the (002) plane on FTO substrates. By employing the magnetron sputtering technique to deposit a tungsten (W) top metal electrode onto these ZnO thin films, we successfully realize a W/ZnO/FTO memory device that exhibits self-rectifying and forming-free resistive switching characteristics. Notably, the as-prepared device demonstrates impressive nonvolatile and bipolar resistive switching behavior, with a high resistance ratio (RHRS/RLRS) exceeding two orders of magnitude at a reading voltage of 0.1 V. Moreover, it exhibits ultralow set and reset voltages of approximately +0.5 V and −1 V, respectively, along with exceptional durability. In terms of carrier transport properties, the low resistance state of the device is dominated by ohmic conduction, whereas the high resistance state is characterized by trap-controlled space-charge-limited current conduction. This work highlights the potential of the ZnO-based W/ZnO/FTO memory device as a promising candidate for future high-density nonvolatile memory applications.

Nonvolatile ferroelectric resistive switching in α-In2Se3(2H) ferroelectric semiconductor junctions

Emerging two-dimensional van der Waals (vdW) based ferroelectric semiconductor junctions (FSJs) are promising for low-power and high-density applications. In this work, we report the vdW α-In2Se3(2H) based FSJs of different metal-In2Se3 interfaces. All vertical devices emerge with the nonvolatile ferroelectric resistive switching behavior. The Cr/α-In2Se3(2H)/Au FSJs show a typical ferroelectric resistive switching behavior under ∼1.0 V applied voltage. The switching voltage of the Ag/α-In2Se3(2H)/Au FSJs could be further decreased from 1.0 V to 0.8 V because of Ag migrations and ferroelectric reversal. Further, by optimizing the metal-In2Se3 interfaces, the Ag/α-In2Se3(2H)/Pt FSJs exhibit the ultralow switching voltage (∼0.3 V), excellent endurance (>225 cycles) and retention (>1 × 104 s). The results suggest that vdW α-In2Se3(2H) ferroelectric has great potential for low-power memristive devices.

Building Uniformly Structured Polymer Memristors via a 2D Conjugation Strategy for Neuromorphic Computing.

Polymer memristors represent a highly promising avenue for the advancement of next-generation computing systems. However, the intrinsic structural heterogeneity characteristic of most polymers often results in organic polymer memristors displaying erratic resistive switching phenomena, which in turn lead to diminished production yields and compromised reliability. In this study, a 2D conjugated polymer, named PBDTT-BPQTPA, is synthesized by integrating the coplanar bis(thiophene)-4,8-dihydrobenzo[1,2-b:4,5-b]dithiophene (BDTT) as an electron-donating unit with a quinoxaline derivative serving as an electron-accepting unit. The incorporation of triphenylamine groups at the quinoxaline termini significantly enhances the polymer's conjugation and planarity, thereby facilitating more efficient charge transport. The fabricated polymer memristor with the structure of Al/PBDTT-BPQTPA/ITO exhibits typical non-volatile resistive switching behavior under high voltage conditions, along with history-dependent memristive properties at lower voltages. The unique memristive behavior of the device enables the simulation of synaptic enhancement/inhibition, learning algorithms, and memory operations. Additionally, the memristor demonstrates its capability for executing logical operations and handling decimal calculations. This study offers a promising and innovative approach for the development of artificial neuromorphic computing systems.

Solution-Processed Robust Multifunctional Memristor of 2D Layered Material Thin Film.

Memristors have gained significant attention recently due to their unique ability to exhibit functionalities for brain-inspired neuromorphic computing. Here, we demonstrate a high-performance multifunctional memristor using a thin film of liquid-phase exfoliated (LPE) 2D MoS2 pinched between two electrodes. Nanoscale inspection of a solution-processed MoS2 thin film using scanning electron and scanning probe microscopies revealed the high-quality and defect-free nature. Systematic current-voltage (I-V) characterizations depict a facile, nonvolatile resistive switching behavior of our 2D MoS2 thin film device with a current On/Off ratio of 103 and energy cost of only a few picojoules. Excellent performance metrics, including at least 103 cycle endurance, 104 s retention, and switching speed down to a few nanoseconds, reflect robust high-performance data storage capability. Charge carriers trapping and detrapping at the sulfur vacancy defect sites in MoS2 nanosheets mainly display the resistive switching property, supported by the impedance analysis and theoretical fitting results. Multifunctionality is leveraged through implementing two-input logic gate operations, edge computation, and crucial adaptive learning via a Pavlov's dogs experiment. Overall, our solution-processed MoS2 memristor has the potential for tremendous future opportunities in integrated circuits and different computing paradigms, including energy-efficient neuromorphic computing hardware in artificial intelligence.

Non-volatile resistive switching behavior and time series analysis of Ag/PVA-graphene oxide/Ag device

Non-volatile memory devices have been getting significant attention from researchers worldwide in recent years due to their application in resistive random access memory and neuromorphic computing. Here, we have fabricated polyvinyl alcohol-graphene oxide (PVA-GO) composite as an active material for the resistive switching with different concentrations of GO (0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 wt. % GO solution) dispersed in 5 wt. % PVA matrix in a 2:1 volume ratio. We demonstrate the non-volatile forming free resistive switching properties of Ag/PVA-GO/Ag devices. Structural properties of PVA-GO composites are established from the x-ray diffraction pattern, which indicates the complete dispersion of GO inside the PVA matrix. The Ag/PVA-GO-0.1 wt. %/Ag device shows better bipolar resistive switching at VSET ∼ 0.4 V and VRESET at ∼−0.8 V. This device indicates well-resolved two distinct states at a read voltage of 0.1 V in endurance and retention measurements. The fabricated device switches successfully tested for 2.5 × 103 cycles and retains its state for 3.36 × 103 s without any observable degradation. Furthermore, the non-volatile retention property was modeled using time series analysis. For this, Holt–Winter's exponential smoothing technique was utilized. Additionally, the charge–flux linkage characteristic shows the double-valued function, and time domain–charge and time domain–flux show asymmetric behaviors. The electrical conduction mechanism exhibits ohmic behavior in the entire region of the low resistance state and the lower voltage region of the high resistance state. In the high-voltage region of the high resistance state, the space charge-limited conduction mechanism is observed. The resistive switching behavior is explained with the help of an appropriate model.

Photoinduced Nonvolatile Resistive Switching Behavior in Oxygen-Doped MoS2 for a Neuromorphic Vision System.

Controlling resistance by external fields provides fascinating opportunities for the development of novel devices and circuits, such as temperature-field-induced superconductors, magnetic-field-triggered giant magnetoresistance devices, and electric-field-operated flash memories. In this work, we demonstrate a light-triggered nonvolatile resistive switching behavior in oxygen-doped MoS2. The two-terminal devices exhibit stable light-modulated resistive switching characteristics and optically tunable synaptic properties with an on/off ratio of up to 104. The integrated device with crossbar architecture enables simultaneous image sensing, preprocessing, and storage in a single device, thereby increasing the training efficiency and recognition rate of image recognition tasks. This work presents a novel pathway to develop the next generation of light-controlled memory and artificial vision systems for neuromorphic computing.

Two-dimensional growth of Cu-based materials with a nonvolatile resistive switching behavior

Two-dimensional (2D) crystals have attracted much attention to the application in next-generation non-volatile memories due to their interesting structures and features. Herein, we report the controllable synthesis of 2D Cu2SxSe1– x crystals via a facile ambient pressure vapor deposition method. And the planar and vertical devices on the synthesized Cu2SxSe1– x crystals demonstrate a stable nonvolatile resistance switching. Most importantly, the planar Cu2SxSe1–x devices show a bipolar resistance switching behavior with a memory window of ∼103 and a relatively low operating voltage (<1 V). While the vertical Cu2SxSe1–x device exhibits a unipolar switching behavior with a large memory window of ∼105. Our findings in this work broaden the horizon for the in-situ synthesis of 2D materials and enlighten the possibility of related applications in neural synapse and artificial intelligence.

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.

Implementation of threshold- and memory-switching memristors based on electrochemical metallization in an identical ferroelectric electrolyte

The use of an identical electrolyte in electrochemical metallization (ECM)-based neuron and synaptic devices has not yet been achieved due to their different resistive-switching characteristics. Herein, we describe ECM devices comprising the same ferroelectric PbZr0.52Ti0.48O3 (PZT) electrolyte, which can sustain both neuron and synaptic behavior depending on the identity of the active electrode. The Ag/PZT/La0.8Sr0.2MnO3 (LSMO) threshold switching memristor shows abrupt and volatile resistive switching characteristics, which lead to neuron devices with stochastic integration-and-fire behavior, auto-recovery, and rapid operation. In contrast, the Ni/PZT/LSMO memory switching memristor exhibits gradual, non-volatile resistive switching behavior, which leads to synaptic devices with a high on/off ratio, low on-state current, low variability, and spike-timing-dependent plasticity (STDP). The divergent behavior of the ECM devices is attributed to greater control of cation migration through the ultrathin ferroelectric PZT. Thus, ECM devices with an identical ferroelectric electrolyte offer promise as essential building blocks in the construction of high-performance neuromorphic computing systems.

A Facile Hydrothermal Synthesis and Resistive Switching Behavior of α-Fe2O3 Nanowire Arrays.

A facile hydrothermal process has been developed to synthesize the α-Fe2O3 nanowire arrays with a preferential growth orientation along the [110] direction. The W/α-Fe2O3/FTO memory device with the nonvolatile resistive switching behavior has been achieved. The resistance ratio (RHRS/RLRS) of the W/α-Fe2O3/FTO memory device exceeds two orders of magnitude, which can be preserved for more than 103s without obvious decline. Furthermore, the carrier transport properties of the W/α-Fe2O3/FTO memory device are dominated by the Ohmic conduction mechanism in the low resistance state and trap-controlled space-charge-limited current conduction mechanism in the high resistance state, respectively. The partial formation and rupture of conducting nanofilaments modified by the intrinsic oxygen vacancies have been suggested to be responsible for the nonvolatile resistive switching behavior of the W/α-Fe2O3/FTO memory device. This work suggests that the as-prepared α-Fe2O3 nanowire-based W/α-Fe2O3/FTO memory device may be a potential candidate for applications in the next-generation nonvolatile memory devices.

The Effect of Nitrogen Annealing on the Resistive Switching Characteristics of the W/TiO2/FTO Memory Device

In this paper, the effect of nitrogen annealing on the resistive switching characteristics of the rutile TiO2 nanowire-based W/TiO2/FTO memory device is analyzed. The W/TiO2/FTO memory device exhibits a nonvolatile bipolar resistive switching behavior with a high resistance ratio (RHRS/RLRS) of about two orders of magnitude. The conduction behaviors of the W/TiO2/FTO memory device are attributed to the Ohmic conduction mechanism and the Schottky emission in the low resistance state and the high resistance state, respectively. Furthermore, the RHRS/RLRS of the W/TiO2/FTO memory device is obviously increased from about two orders of magnitude to three orders of magnitude after the rapid nitrogen annealing treatment. In addition, the change in the W/TiO2 Schottky barrier depletion layer thickness and barrier height modified by the oxygen vacancies at the W/TiO2 interface is suggested to be responsible for the resistive switching characteristics of the W/TiO2/FTO memory device. This work demonstrates the potential applications of the rutile TiO2 nanowire-based W/TiO2/FTO memory device for high-density data storage in nonvolatile memory devices.

Effect of long chain fatty acids on the memory switching behavior of tetraindolyl derivatives.

Non-volatile memory devices using organic materials have attracted much attention due to their excellent scalability, fast switching speed, low power consumption, low cost etc. Here, we report both volatile as well as non-volatile resistive switching behavior of p-di[3,3'-bis(2-methylindolyl)methane]benzene (Indole2) and its mixture with stearic acid (SA). Previously, we have reported the bipolar resistive switching (BRS) behavior using 1,4-bis(di(1H-indol-3-yl)methyl)benzene (Indole1) molecules under ambient conditions [Langmuir 37 (2021) 4449-4459] and complementary resistive switching (CRS) behavior when the device was exposed to 353 K or higher temperature [Langmuir 38 (2022) 9229-9238]. However, the present study revealed that when the H of -NH group of Indole1 is replaced by -CH3, the resultant Indole2 molecule-based device showed volatile threshold switching behaviour. On the other hand, when Indole2 is mixed with SA at a particular mole fraction, dynamic evolution of an Au/Indole2-SA/ITO device from volatile to non-volatile switching occurred with very good device stability (>285 days), memory window (6.69 × 102), endurance (210 times), data retention (6.8 × 104 s) and device yield of the order of 78.5%. Trap controlled SCLC as well as electric field driven conduction was the key behind the observed switching behaviour of the devices. In the active layer, trap centers due to the SA network may be responsible for non-volatile characteristics of the device. Observed non-volatile switching may be a potential candidate for write once read many (WORM) memory applications in future.

MoTe2-based low energy consumption artificial synapse for neuromorphic behavior and decimal arithmetic

Two-dimensional material-based memristors have shown attractive research prospects as brain-like devices for neuromorphic computing. Among them, transition metal dichalcogenides–based memristors have proved to be one of the most promising competitors. In this work, a two-dimensional memristor based on MoTe2 nanosheets was fabricated and demonstrated. The experimental results illustrate that the two-terminal synaptic based on the Ag/MoTe2/ITO structure exhibits stable bipolar and non-volatile resistive switching characteristics attributed to the controllable formation and rupturing of silver conductive filaments. The device can be successively modulated by a pulse train with a minimum pulse width of 40 ns. More interestingly, the energy consumption of the device to complete one write event is only 74.2 pJ. In addition, biological synaptic behaviors, such as excitatory postsynaptic current gain properties, long-term potentiation (LTP)/long-term depression, spike-timing-dependent- plasticity, short-term plasticity, long-term potentiation (LTP), paired-pulse facilitation, post-tetanic potentiation, and learning-experimental behaviors were mimicked faithfully. Finally, the decimal arithmetic application was introduced to the device, and it is confirmed that addition and multiplication functions can be performed. Therefore, the artificial synapse based on MoTe2 nanosheets not only exhibits the stable non-volatile resistive switching behavior but also facilitates the development of low-energy consumption neuromorphic computing chips based on transition metal dichalcogenides.

Advances in flexible non-volatile resistive switching memory based on organic poly (3, 4-ethylenedioxythio phene): Poly (styrenesulfonate) film

In this work, the resistive switching memory has been investigated in conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) with aluminium (Al) and indium tin oxide (ITO) acting as electrodes. Current-voltage (I-V) characteristics of the fabricated Al/PEDOT:PSS/ITO flexible Polyethylene terephthalate substrate device reveal a non-volatile resistive switching behaviour. The memory device demonstrates resistive switching non-volatile memory with ION/IOFF current ratio between the high resistance state (HRS) and low resistance state (LRS) up to 104. Both the HRS and LRS of the memory devices are stable, showing no significant change in value of ION/IOFF current ratio, which is maintained at 104 in magnitude under continuous read-out testing for 100 cycles at 90º bending angle, and also retention time of 33 min that confirms the device durability and non-volatility. The charge transport mechanism of the fabricated non-volatile organic devices is governed by space-charge limited conduction. It is proposed that the reduction and oxidation of PEDOT:PSS film might be the switching mechanism. Interestingly, the performance of the memory device revealed no detectable degradation and remained identical even after bending the device from 70 to 160° angles, representing excellent flexibility. Besides, the lowest power and the critical compliant current for resistive switching are determined. The power density for 180° (without bending), 160°, 90° and 70° bending angles is ∼ 30 Wm−2. It demonstrates that for a small range of compliance current, our device showed more power capacity with lower voltage consumption, which makes it a potential candidate for low power consumption flexible non-volatile memory devices.

Co-existence of bipolar nonvolatile and volatile resistive switching based on WO3 nanowire for applications in neuromorphic computing and selective memory

A two-terminal memristor can be used for information memory and logic operation as well as serving as an artificial synapse for neuromorphic computing. Selective memory with some enjoyable information to be remembered and other to be screened out can be emulated by an artificial synapse. In this work, a memristor based on a single WO3 nanowire can be constructed, which demonstrates the co-existence of bipolar nonvolatile and volatile resistive switching (RS) behaviors that can be tuned by the amplitude of the operation voltage. For small operation voltages (2 V), the device demonstrates nonvolatile analog RS, which can be utilized as an artificial synapse with long- and short-term plasticity. The learning–forgetting experience of human can be emulated based on the artificial synapse. Moreover, the artificial synapse can be used for image recognition with the recognition accuracy up to 94% for small hand-written image. On the other hand, volatile RS can be observed with large operation voltages (6 V). Furthermore, based on the diverse nonvolatile and volatile RS behaviors, selective memory can be emulated. Our fabricated memristor can be used as an artificial synapse to achieve image recognition and to emulate selective memory, which paves a way to construct smart neuromorphic systems facing complex information.

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.

α-MnO2 nanorods-based memristors with nonvolatile resistive switching behavior

Low dimensional micro or nano materials, which have unique physical, chemical, and electrical properties, have recently gained attention in the preparation of nonvolatile memory device. In this work, one dimensional (1D) α-MnO2 nanorods with diameter of ∼100 nm and length of ∼837 nm was synthesized by hydrothermal method under 160 °C for 12 h, and then it was used as the dielectric layer of memristive device. The resistive switching (RS) behavior of as-prepared memristive device with Ag/α-MnO2/Ti sandwich structure demonstrates nonvolatile memory characteristics. The conduction mechanism of abrupt RS phenomenon can be explained by the formation and fracture of conductive filaments composed of Ag ions and oxygen vacancy. This work lays a foundation for understanding the physical mechanism of memristive system and the development of low dimensional materials-based memristive devices.

Realization of volatile and non-volatile resistive switching with N-TiO2 nanorod arrays based memristive devices through compositional control

It is attractive to manipulate the volatile and non-volatile resistive switching behaviors of memristors to create genuine neuromorphic systems such as artificial neural networks (ANNs) and spiking neural networks (SNNs). To investigate the above behaviors, nitrogen has been introduced into TiO2 nanorod arrays (TiO2 NRAs) by hydrothermal processing. X-ray photoelectron spectroscopy (XPS) analysis shows that both lattice and interstitial nitrogen are incorporated into the TiO2 NRAs. Nitrogen doped TiO2 NRAs (N-TiO2 NRAs) based memristive devices with different contents of lattice nitrogen were investigated systematically. The results show that non-volatile restive switching is achieved at up to a relative lattice nitrogen content of 21%, with volatile switching behavior above this value. The volatile memristive devices show similar spiking and decay features to the Leaky Integrate-and-Fire (LIF) model. The lifetime of the decay process of the volatile devices rang from 0.029 to 1.835 s. The longest lifetime is obtained when the relative content of lattice nitrogen is about 70%. The volatile behavior is related to the large defect concentration, caused by nitrogen doping. The proposed nitrogen engineered memristive devices could pave the way to achieving a physical neuromorphic system.

Colloidal MoS2 quantum dots for high-performance low power resistive memory devices with excellent temperature stability

Conventional memory technologies are facing enormous problems with downscaling, and are hence unable to fulfill the requirement of big data storage generated by a huge explosion of digital information. A resistive random access memory device (RRAM) is one of the most emerging technologies for next-generation computing data storage owing to its high-density stacking, ultrafast switching speed, high non-volatility, multilevel data storage, low power consumption, and simple device structure. In this work, colloidal MoS2 quantum dots (QDs) embedded in an insulating matrix of poly-(4vinylpyridine) (PVP) were used as an active layer to fabricate a RRAM device. The MoS2 QDs-PVP based RRAM device reveals an excellent nonvolatile resistive switching (RS) behavior with a maximum current on-off ratio (ION/IOFF) of 105. High endurance, long retention time, and successive “write-read-erase-read” cycles indicate high-performance RRAM characteristics. The ultimate power consumption by this RRAM device is considerably low for energy saving. In addition, the MoS2 QDs-PVP based device shows RS behavior even at 130 °C. High ION/IOFF, low operating power, high endurance, long retention time, and excellent stability with temperatures reveal that the MoS2 QDs-PVP based device can be a promising candidate for high-performance low power RRAM devices that can be operated at relatively higher temperatures.

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

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