Nonvolatile Memory Effect Research Articles

Bottom-up synthesized crystalline boron quantum dots with nonvolatile memory effects through one-step hydrothermal polymerization of ammonium pentaborane and boric acid

Crystalline BQDs are synthesized through a bottom-up strategy and used to fabricate a BQD–PVP memory device with nonvolatile rewritable memory effects.

Proton-responsive azulene-based conjugated polymer with nonvolatile memory effects

We report an azulene-based conjugated polymer, PAV, which exhibits proton-gated and electrical-gated changes in its conductivity.

Bulk Heterojunction Optoelectrical Switching Devices Fabricated Using Nonfullerene Acceptor Y6: Aggregation-Induced Emission Polymer Blend Active Layers

Abstract By using poly {[9,9-dioctyl-9H-fluorene]-alt-(1,1,2,2-tetra-phenylethene)} (POFTPE) as an electron donor, and Y6 (or C60) as electron acceptor, solution-processed bulk heterojunction optoelectronic switching devices with a configuration of ITO/POFTPE:Y6(C60)/ITO, which can respond to both the optical and electrical stimuli, have been successfully fabricated. Both the electron transfer and energy transfer from POFTPE to Y6 will occur simultaneously in the blends system under light illumination, while no energy transfer between POFTPE and C60 occurs, expect for electron transfer. Both the ITO/POFTPE:Y6/ITO and ITO/POFTPE:C60/ITO devices show typical nonvolatile rewritable memory effect in the dark or under light illumination. Upon illumination with different wavelength lights, the switching bias window (Δ|VON-VOFF|), switching-on voltage and the ON/OFF current ratio of the ITO/POFTPE:Y6(5:1)/ITO device decrease with decreasing the incident light wavelength due to the increased free charge carrier concentration caused by light illumination. In contrast to the POFTPE:Y6 blends, the POFTPE:C60 blends-based device measured in the dark shows smaller switch-on voltage, ON/OFF current ratio and switching bias window under the same experimental conditions. This work shows one of the very promising strategies for exploring the nonvolatile multilevel storage by tailoring optoelectronic switching and memory performance of the materials via illumination with different wavelength lights.

Analog Memristive Characteristics of Square Shaped Lanthanum Oxide Nanoplates Layered Device.

Square-shaped or rectangular nanoparticles (NPs) of lanthanum oxide (LaOx) were synthesized and layered by convective self-assembly to demonstrate an analog memristive device in this study. Along with non-volatile analog memory effect, selection diode property could be co-existent without any implementation of heterogeneous multiple stacks with ~1 μm thick LaOx NPs layer. Current–voltage (I–V) behavior of the LaOx NPs resistive switching (RS) device has shown an evolved current level with memristive behavior and additional rectification functionality with threshold voltage. The concurrent memristor and diode type selector characteristics were examined with electrical stimuli or spikes for the duration of 10–50 ms pulse biases. The pulsed spike increased current levels at a read voltage of +0.2 V sequentially along with ±7 V biases, which have emulated neuromorphic operation of long-term potentiation (LTP). This study can open a new application of rare-earth LaOx NPs as a component of neuromorphic synaptic device.

Rectifying optoelectronic memory based on WSe2/graphene heterostructures.

van der Waals heterostructures composed of two-dimensional materials vertically stacked have been extensively studied to develop various multifunctional devices. Here, we report WSe2/graphene heterostructure devices with a top floating gate that can serve as multifunctional devices. They exhibit gate-controlled rectification inversion, rectified nonvolatile memory effects, and multilevel optoelectronic memory effects. Depending on the polarity of the gate voltage pulses (VGp), electrons or holes can be trapped in the floating gate, resulting in rectified nonvolatile memory properties. Furthermore, upon repeated illumination with laser pulses, positive or negative staircase photoconductivity is observed depending on the history of VGp, which is ascribed to the tunneling of electrons or holes between the WSe2 channel and the floating gate. These multifunctional devices can be used to emulate excitatory and inhibitory synapses that have different neurotransmitters. Various synaptic functions, such as potentiation/depression curves and spike-timing-dependent plasticity, have been also implemented using these devices. In particular, 128 optoelectronic memory states with nonlinearity less than 1 can be achieved by controlling applied laser pulses and VGp, suggesting that the WSe2/graphene heterostructure devices with a top floating gate can be applied to optoelectronic synapse devices.

Organic spin valves with nonvolatile memory using molecular doping

Recently, several multifunctional organic spin valves (OSVs) integrating both magnetoresistance (MR) effect and nonvolatile memory effect were reported. In most cases, single unmodified organic layers were employed, and the underlying mechanism of the memory effect was not fully understood. Here, we present a simple and effective method to achieve nonvolatile memory in OSVs by doping the organic interlayer of the sandwich device, which will introduce traps in the organic interlayer and affect charge and spin transport. The doped OSVs exhibit a current-voltage hysteresis and reversible resistive switching behavior, indicating that the nonvolatile memory is achieved. The trap-controlled space-charge-limited current model can explain the memory effect of the doped OSVs, and combined with spin diffusion theory based on hyperfine interaction it can also explain the corresponding MR changes under different resistance states.

A benzothiadiazole-containing π-conjugated small molecule as promising element for nonvolatile multilevel resistive memory device

A novel 2,1,3-benzothiadiazole (BT)-based donor−acceptor (D−A) type small molecule (NBTC) has been demonstrated for promising application in organic multilevel resistive memory devices. NBTC exhibits excellent nonvolatile ternary memory effects with high ON2/ON1/OFF current ratios of 107.5/103.8/1 and threshold voltages of −2.70 and −4.80 ​V, attributing to the different electron-withdrawing abilities of acceptors that can induce stepwise D−A charge transfer and charge trapping processes. This result suggests that BT-based D−A type materials can hold great promise for achieving ultrahigh-density data-storage devices through the rational D−A modulation, which provides guidelines for designing more proof-of-concept organic memory electronics for big data storage application.

Observation of CCNR-type electrical switching in Zn0.3Mn0.7+xSixFe2−2xO4 spinel ferrite series

A nonvolatile memory effect exhibited by electric field-induced resistance switching has been the topic of intense research not only due to its applications as resistive random access memory but also from the basic physics point of view. Among several binary and ternary mixed oxide compounds, the ones which possess magnetic ions have shown a great promise. Spinel ferrite system Zn0.3Mn0.7+xSixFe2−2xO4 with varying x is investigated for its novel electrical switching properties. Both temperature and applied voltage dependence of current-controlled negative resistance-type electrical switching showed better than 200% of resistive switching ratios. Bulk polycrystalline samples showed composition x dependence of resistive switching. The current–voltage characteristics are modeled for low and high applied field regime, and the presence of space-charge-limiting current is confirmed. Thin films of the ferrite system grown by pulsed laser deposition showed almost nonexistence of resistive switching, suggesting that the bulk composition of the compound has a major role to play against the film–electrode interface.

Resistive switching memory effects in p-type hydrogen-treated CuO nanowire

Nanowire (NW)-based resistive switching device offers an ideal platform to develop a nanoscale-memristive device for next-generation memory and computing. The present study developed a p-type hydrogen-treated CuO NW memory device by using hydrogen annealing. The hydrogen-treated CuO NW, which is mainly composed of Cu2O, exhibited a resistive switching non-volatile memory effect and demonstrated low electric-field device operation with ∼3 × 106 V/m and high ON/OFF ratio up to 107. The hole conduction path formation/rapture mechanism based on the redox reaction of CuO was proposed as a resistive switching mechanism.

Bio-inspired flexible vibration visualization sensor based on piezo-electrochromic effect

Monitoring structural vibration can provide quantitative information for both structural health evaluations and early-warning maintenance. The most classic vibration-based structural health monitoring is equipped with piezoelectric accelerometers, which is expensive and inconvenient due to cumbersome and time-consuming sensor installation and high power-consumptive data acquisition systems. One other main challenge with these systems is the inherent limitations for multi-point monitoring in critical elements with curvature due to their non-conformability. Here, inspired by the chameleon, we report a cost-effective, flexible and conformal, self-powered vibration sensor based on elasto-electro-chemical synergistic effect of piezoelectricity and electrochromism. The sensor can provide not only in-situ visualization, but also ex-situ recording of structural vibration due to the non-volatile color memory effect of electrochromism. The passive sensor system is composed of two distinct electronic components — ternary Pb(In1/2Nb1/2)O3Pb(Mg1/3Nb2/3)O3PbTiO3 piezoelectric single crystal ribbon sensors and a solid-state tungsten trioxide electrochromic indicator driven by vibration-induced voltage generated by the piezoelectric ribbons. The proposed piezo-electrochromic based passive non-volatile visualization sensor may find diverse applications in structural health monitoring, smart wallpapers, and medical injury rehabilitation.

Anisotropic magnetoresistance and nonvolatile memory in superlattices of La2/3Sr1/3MnO3 and antiferromagnet Sr2IrO4

Antiferromagnets have attracted considerable interest in the field of spintronics due to their attractive characteristics such as ultrafast spin dynamics and robustness against external magnetic field perturbations. Sr2IrO4 is a rare example of antiferromagnetic semiconductor oxide and has been extensively studied in anisotropic magnetoresistance-based spintronics. However, the anisotropic magnetoresistance of Sr2IrO4 films is usually very small. Herein, we have prepared a (Sr2IrO4)4/(La2/3Sr1/3MnO3)5 superlattice which shows an enhanced anisotropic magnetoresistance compared to Sr2IrO4 film or La2/3Sr1/3MnO3/Sr2IrO4 heterostructure and an obvious nonvolatile memory effect that is comparable to Sr2IrO4 single crystals. Through magnetic measurements, the increased coercivity and the exchange bias at low temperatures reveal the interfacial magnetic coupling between Sr2IrO4 and La2/3Sr1/3MnO3. Additionally, the remarkable anisotropic magnetoresistance and clear hysteresis of anisotropic magnetoresistance with distinct fourfold symmetry can be controlled by temperature and magnetic field. These findings demonstrate that the superlattices of heavy transition metal oxide Sr2IrO4 are excellent platforms for antiferromagnetic spintronics.

Crystalline Semiconductor Boron Quantum Dots.

Zero-dimensional boron structures have always been the focus of theoretical research owing to their abundant phase structures and special properties. Boron clusters have been reported extensively by combining structure searching theories and photoelectron spectroscopy (PES) experiments; however, crystalline boron quantum dots (BQDs) have rarely been reported. Here, we report the preparation of large-scale and uniform crystalline semiconductor BQDs from the expanded bulk boron powders via a facile and efficient probe ultrasonic approach in the acetonitrile solution. The obtained BQDs have 2.46 nm average lateral size and 2.81 nm thickness. Optical measurements demonstrate that a strong quantum confinement effect occurs in the BQDs, implying the increase of the band gap from 1.80 eV for the corresponding bulk to 2.46 eV for the BQDs. By injecting the BQDs into poly(vinylpyrrolidone) as an active layer, a BQD-based memory device is fabricated that shows a rewriteable nonvolatile memory effect with a low transition voltage of down to 0.5 V and a high on/off switching ratio of 103 as well as a good stability.

Surface traps-related nonvolatile resistive switching memory effect in a single SnO2:Sm nanowire

For nanostructure SnO2, it is very difficult for its electric properties to accurately control due to the presence of abundant surface states. The introduction of Sm can improve the traps in surface space charge region of SnO2 nanowires, resulting in a controllable storage charge effect. For the single nanowire-based two-terminal device, two surface state-related back-to-back diodes are formed. At a relatively large voltage, electrons can be injected into the traps in surface space charge region from negative electrode, resulting in a decrease of surface barrier connected with negative electrode, and contrarily electrons can be extracted from the traps in surface space charge region into positive electrode, resulting in an increase of surface barrier connected with positive electrode. The reversible injection and extraction induce a nonvolatile resistive switching memory effect.

In Situ Preparation and Unique Electrical Behaviors of Gold@Hollow Polyaniline Nanospheres through Recovery of Gold from Simulated e-Waste

Abstract One of the most effective ways to solve the dilemma between resources shortages and increasing demand is to develop a cost-effective approach for recovery and reuse of the precious metals (especially Au and Ag) derived from e-wastes (electronic devices and the components thereof), which will most likely be driven by breakthroughs in environmentally friendly methodologies that combine the economy of scale with function. Here a facile and novel approach is described for the recovery of gold from simulated e-wastes by using hollow polyaniline nanospheres (P(VAn-g-PANI)) in which PANI and its derivatives can not only be used to reduce Au3+ to Au0 from the metal salts, but also be used to stabilize the achieved polymer nanosphere-supported Au nanoparticles (Au@P(VAn-g-PANI)). The Au@P(VAn-g-PANI) was directly used to fabricate electronic devices with a configuration of Al/Au@P(VAn-g-PANI) + PVA]/ITO, in which Au@P(VAn-g-PANI) was uniformly integrated into poly(vinyl alcohol) (PVA) as electrically insulating matrix. When the Au/N molar ratio in P(VAn-g-PANI) reached 1:10, the device could be electrically erased and reprogrammed showing typical nonvolatile rewritable memory effect, with an ON/OFF current ratio exceeding 105, a turn-on voltage of −1.85 V and a turn-off voltage of 2.90 V. In the case of Au/N molar ratio of 1:1, the corresponding device exhibited conductor behaviour. This work opens a way that can both recycle gold in situ from e-wastes and fabricate electronic devices by using polymer nanosphere-supported Au nanoparticles.

Fluorenone/carbazole based bipolar small molecules for non-volatile memory devices

Developing new-style non-volatile memory is an important part to solve von Neumann bottleneck. Among numerous studies of memory device, resistive random-access memory (RRAM) is widely researched for their simple geometrical structure and high integration density. In recent decades, organic RRAM catches many researchers’ attention for their superiorities such as outstanding flexibility, simple solution processability, low-cost fabrication and tunable functionalities by changing the chemical groups. Herein, a series of organic small molecules 2,7-di(9H-carbazol-9-yl)-9H-fluoren-9-one (FLOCZ) and 2,7-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-fluoren-9-one (FLOBCZ) are synthesized and their band structures and electronic states are systematically studied with the assistance of density function theory (DFT). Then, using simple solution-processing approach, FLOCZ/FLOBCZ based RRAMs are fabricated and their memory characteristics are studied. The as-fabricated Ag/FLOBCZ/ITO RRAM exhibits non-volatile memory effect with a memory window up to 7 × 103 and data retention time of more than 2 × 104 s, which can meet the requirement of data storage. Meanwhile, by controlling compliance current on the RRAM precisely, multi-level data storage can be implemented experimentally. Our work extends the applications of organic small molecule and promotes the evolution of organic RRAM.

Bipolar resistive switching, synaptic plasticity and non-volatile memory effects in the solution-processed zinc oxide thin film

The memristive devices are getting a lot of interest in recent years due to its applications in the field of resistive memory and brain-inspired computing. In the present work, we have developed a ZnO memristive device using the reflux method. We have demonstrated non-volatile memory properties and mimicked the basic synaptic properties of using Al/ZnO/FTO thin film device. The structural, morphological and compositional studies of ZnO thin film were carried out by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The co-existence of analog and digital resistive switching in a ZnO memristive device was achieved by properly tuning the external electrical stimulus. The developed ZnO memristive device mimics the basic synaptic properties such as potentiation-depression, symmetric Hebbian and antisymmetric Hebbian learning rules at a lower voltage bias (±1 V to ± 3 V). Whereas, non-volatile memory properties (endurance and retention) were achieved at a higher voltage bias (±4 V to ± 6 V). The Al/ZnO/FTO thin film memory device shows good resistive switching memory properties such as 104 endurance cycles and 104 s retention period with good uniformity during the cycle to cycle operation. The detailed analysis of I–V results suggested that the Schottky conduction model is responsible for the analog mode of operation, whereas, space charge limited current governs the device dynamics during the digital mode of operation. A possible resistive switching model is also presented.

Facile Synthesis of Ti3C2Tx-Poly(vinylpyrrolidone) Nanocomposites for Nonvolatile Memory Devices with Low Switching Voltage.

MXenes, an emerging class of two-dimensional (2D) transition-metal carbide materials, have received increasing attention for their interesting physiochemical properties. For not only MXenes but also other 2D materials, delamination is a requisite step for the exploitation of their unique properties. In this work, a facile method for exfoliating Ti3C2Tx MXene to nanosheets of small size with the aid of poly(vinylpyrrolidone) (PVP) is designed, which has never been reported to our knowledge. Since both hydrophobic methylene groups and hydrophilic amide groups are provided with PVP, this method is applicable in a wide range of solvents, such as ethanol, water, and chloroform. Considering the charge detrapping and trapping behavior of 2D transition-metal materials in PVP dielectric, a memory device with the configuration of reduced graphene oxide (rGO)/Ti3C2Tx-PVP/Au is directly fabricated with these well-dispersed Ti3C2Tx-PVP composites by the solution process technique. Interestingly, the resultant device exhibits a typical bistable electrical switching, ultralow switching voltage (∼0.9 V), and a nonvolatile rewritable memory effect with the function of flash. This work might pave the way of using MXenes for future data storage, which is an indispensable field nowadays.

Trap‐Related Nonvolatile Negative Photoconductivity in a Single Ag@Al2O3 Hybrid Nanorod for a Photomemory with Light‐Writing and Bias‐Erasing

AbstractFor zero band‐gap metal Ag and ultrawide band‐gap Al2O3, it is difficult to produce impressive photoresponse to visible light due to the limitation of energy gaps. Herein, it is demonstrated that individual Ag@Al2O3 hybrid nanorods, synthesized by a two‐stage hydrothermal method and followed by thermal reduction annealing, can show excellent negative photoconduction of about 400 nm violet and 800 nm near‐infrared lights at room temperature. Moreover, the light‐induced high resistance state (HRS) is well maintained at relatively low operation bias after the removal of illumination, indicative of a nonvolatile memory effect. More importantly, the device is back to its initial low resistance state (LRS) after subsequently being applied a relatively large bias, suggestive of an erasable effect with large bias. In the hybrid nanorods, Ag nanoparticles serve as trap centers and can capture and store charges. Under the illumination of sub‐band‐gap light, trapped charges are excited, resulting in an HRS due to emptying the traps. On the contrary, a large external electric field triggers charges to be injected into traps in dark, resulting in an LRS. Regarding a superior negative photoswitching with light‐writing and bias‐erasing memory, Ag@Al2O3 nanohybrids have a tremendous potential in optical sensors and nonvolatile photomemory applications.

Ferroelectric materials for neuromorphic computing

Ferroelectric materials are promising candidates for synaptic weight elements in neural network hardware because of their nonvolatile multilevel memory effect. This feature is crucial for their use in mobile applications such as inference when vector matrix multiplication is performed during portable artificial intelligence service. In addition, the adaptive learning effect in ferroelectric polarization has gained considerable research attention for reducing the CMOS circuit overhead of an integrator and amplifier with an activation function. In spite of their potential for a weight and a neuron, material issues have been pointed out for commercialization in conjunction with CMOS processing and device structures. Herein, we review ferroelectric synaptic weights and neurons from the viewpoint of materials in relation to device operation, along with discussions and suggestions for improvement. Moreover, we discuss the reliability of HfO2 as an emerging material and suggest methods to overcome the scaling issue of ferroelectrics.

Bistable electrical switching and nonvolatile memory effect in poly (9,9-dioctylfluorene-2,7-diyl) and multiple-walled carbon nanotubes

The Suzuki coupling reaction was used to synthesize the poly (9,9-dioctylfluorene-2,7-diyl) (PFO), MWCNTs were doped in PFO by physical blending. Memristors were prepared with PFO and PFO:MWCNTs as active layer, and the effect of MWCNTs content on the electrical characteristics of the device was proved. The results reveal that the devices with doped and undoped MWCNTs had bistable nonvolatile memory behavior. After doping MWCNTs, the ON/OFF state current ratio is obviously improved and the device with 1.6% MWCNTs content shows the maximum ON/OFF curent ratio of 2.6 × 103 and lower threshold voltage approximately −0.7 V. Futhermore, the device remains stable for 3 h and the curent has no obvious change after 9000 read cycles, whether it is ON state or OFF state.