Multilevel Devices Research Articles

Solution processed bilayer junction of silk fibroin and semiconductor quantum dots as multilevel memristor devices

Silkworm protein is integrated with semiconductor quantum dots (CdSe) to form bi-layer electrical memory devices. These films are individually spin coated on ITO surface to form ITO-silk fibroin:CdSe-metal junctions. These materials are characterized by DSC, TGA, FTIR, UV–visible absorbance, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) and TEM to understand their physical properties. The charge transport is carried out on the above devices by cyclic voltage scan in the sequence zero-positive-zero-negative-zero to study their electrical memory switching behavior. Devices exhibit multilevel electrical switching both in the forward and in the reverse regions that are quite symmetric, the ON/OFF ratios are well resolved. These junctions posses a high repeatability with a good endurance and hence can be important interfaces for electrical information storage applications. The observed results of the above memristors are explained in terms of their energy band diagram, it is observed that in these interfaces monopolar charge transport of holes is the dominant mechanism that is further supported by multiple hole trapping centers both in CdSe and silk fibroin energy gaps.

High-Performance Nonvolatile Organic Field-Effect Transistor Memory Based on Organic Semiconductor Heterostructures of Pentacene/P13/Pentacene as Both Charge Transport and Trapping Layers.

Nonvolatile organic field‐effect transistor (OFET) memory devices based on pentacene/N,N′‐ditridecylperylene‐3,4,9,10‐tetracarboxylic diimide (P13)/pentacene trilayer organic heterostructures have been proposed. The discontinuous n‐type P13 embedded in p‐type pentacene layers can not only provide electrons in the semiconductor layer that facilitates electron trapping process; it also works as charge trapping sites, which is attributed to the quantum well‐like pentacene/P13/pentacene organic heterostructures. The synergistic effects of charge trapping in the discontinuous P13 and the charge‐trapping property of the poly(4‐vinylphenol) (PVP) layer remarkably improve the memory performance. In addition, the trilayer organic heterostructures have also been successfully applied to multilevel and flexible nonvolatile memory devices. The results provide a novel design strategy to achieve high‐performance nonvolatile OFET memory devices and allow potential applications for different combinations of various organic semiconductor materials in OFET memory.

Design of Ternary Neural Network With 3-D Vertical RRAM Array

Recently, 2-D cross-point array of resistive random access memory (RRAM) has been proposed for implementing the weighted sum and weight update operations to accelerate the neuro-inspired learning algorithms on chip. This paper aims to extend such 2-D cross-point array to 3-D vertical array for storing and computing the large-scale weight matrices in the neural network. Considering the fabrication and 3-D integration of analog synapses (i.e., multilevel RRAM devices) are premature at this stage, we propose using today’s available digital or binary RRAM devices for implementing a ternary neural network, which aggressively reduces the weight precision to ternary levels (+1, 0,−1) for the weighted sum in both feedforward and backward inference, while the multiple 3-D layers could serve for accumulating the small errors in a higher precision format for weight update. Compared to the 2-D implementation, the proposed 3-D vertical implementation shows larger read/write margin for weighted sum/weight update, smaller latency, and energy consumption for weight update. This paper demonstrates the attractiveness for building a monolithic 3-D neuromorphic hardware platform.

A Novel Bat‐Shaped Dicyanomethylene‐4H‐pyran‐Functionalized Naphthalimide for Highly Efficient Solution‐Processed Multilevel Memory Devices

Small-molecule-based multilevel memory devices have attracted increasing attention because of their advantages, such as super-high storage density, fast reading speed, light weight, low energy consumption, and shock resistance. However, the fabrication of small-molecule-based devices always requires expensive vacuum-deposition techniques or high temperatures for spin-coating. Herein, through rational tailoring of a previous molecule, DPCNCANA (4,4'-(6,6'-bis(2-octyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)-9H,9'H-[3,3'-bicarbazole]-9,9'-diyl)dibenzonitrile), a novel bat-shaped A-D-A-type (A-D-A=acceptor-donor-acceptor) symmetric framework has been successfully synthesized and can be dissolved in common solvents at room temperature. Additionally, it has a low-energy bandgap and dense intramolecular stacking in the film state. The solution-processed memory devices exhibited high-performance nonvolatile multilevel data-storage properties with low switching threshold voltages of about -1.3 and -2.7 V, which is beneficial for low power consumption. Our result should prompt the study of highly efficient solution-processed multilevel memory devices in the field of organic electronics.

Research on the Method of Liquid Anti-roll of LNG Storage Tank

In this paper, the phenomenon of liquefied natural gas in storage in the roll, take a high-density liquid, multi-level controllable circulation punch injection device, change the past, the top and bottom of the tank discharge tube discharge tube mode, stratified unloading mode the measuring device of collected density, temperature, liquid level data, through this device controlled discharge nozzle layered, layers of liquid through the fill tube is connected, into the tank. After the tanks in operation, when the unloading of the LNG density and density of LNG storage tank is not at the same time, the use of this device, different densities of LNG will automatically mix, does not produce significant stratification, thus greatly reducing the rollover occurred probability, increase in liquefied natural gas storage and transportation security.

Failure Analysis of the Multi-Level Series Rotary Seal Device under High-Pressure Water

High-pressure water jets are used to assist roadheaders in breaking hard rock. The failure life of the high-pressure rotary seal (HPRS) is significant, due to how it affects the safety and efficiency of the roadheader. Here we investigate the mechanical behaviour of the HPRS with a series of experiments. Single-level rotary seal device based studies were conducted to investigate the effect of seal forms, materials, operating pressure and spindle speed on friction torque and leakage. The best seal form from the three kinds of forms was chosen to test the failure life of the multi-level series rotary seal device and the relationships between the operating pressure, spindle speed, temperature, leakage and failure life were analysed. The failure life of rotary seals from Levels 1 to 4 was observed to be 15, 11, 5, and 4 days respectively. The increase in temperature of Levels 1 and 2 was perceived to be slow at the beginning phase of the test, while it rose sharply until the failure occurred, whereas in the case of Levels 3 and 4 it was instantaneous.

Manipulation of Push–Pull System by Functionalization of Porphyrin at β‐Position for High‐Performance Solution‐Processable Ternary Resistive Memory Devices

AbstractThrough tailoring substituents at β‐positions of NiII porphyrin complexes in a push–pull system, multilevel resistive memory devices with high performance have been realized via solution‐processing fabrications. Promising ternary resistive memory behavior has been demonstrated by distinct “OFF”, “ON1” and “ON2” conductivity states with current ratios of 1:104:107, together with low first switching voltage (VTh1=2.1 V), well‐differentiable second threshold voltage (VTh2=3.1 V), low power consumption reading bias (1.0 V) as well as long retention time (>104 seconds), revealing their potential application in the field of ultra high‐density data storage. In contrast to the push–pull system, only a binary logic gate is found in push only or pull only complexes. The present study may provide a new design strategy and inspiration for the development of multistate memory devices through push–pull systems of this type.

Origin of multistate resistive switching in Ti/manganite/SiOx/Si heterostructures

We report on the growth and characterization of Ti/La1/3Ca3/2MnO3/SiO2/n-Si memristive devices. We demonstrate that using current as electrical stimulus unveils an intermediate resistance state, in addition to the usual high and low resistance states that are observed in the standard voltage controlled experiments. Based on thorough electrical characterization (impedance spectroscopy, current-voltage curves analysis), we disclose the contribution of three different microscopic regions of the device to the transport properties: an ohmic incomplete metallic filament, a thin manganite layer below the filament tip exhibiting Poole-Frenkel like conduction, and the SiOx layer with an electrical response well characterized by a Child-Langmuir law. Our results suggest that the existence of the SiOx layer plays a key role in the stabilization of the intermediate resistance level, indicating that the combination of two or more active resistive switching oxides adds functionalities in relation to the single-oxide devices. We understand that these multilevel devices are interesting and promising, as their fabrication procedure is rather simple and they are fully compatible with the standard Si-based electronics.

Highly Reproducible and Regulated Conductance Quantization in a Polymer‐Based Atomic Switch

A detailed understanding of the conductance quantization and resistive switching phenomena in redox‐based memories is crucial for realizing atomic‐scale memory devices and for finding the adequate design principles on which they can be based. Here, the emergence of quantized conductance states and their correlation with resistive switching characteristics in polymer‐based atomic switches are investigated using combinations of current–voltage measurements and first‐principles density functional theory (DFT) simulations. Various conductance states, including integer and half‐integer multiples of a single atomic point contact and fractional conductance variations, are observed in an Ag/polyethylene oxide/Pt device under sweeping of bias voltage. Moreover, highly controllable and reproducible quantized conductance behaviors by tuning the voltage sweep rate and the sweep voltage range, suggesting well‐controlled formation of the atomic point contact, are demonstrated. The device also exhibits longer retention times for higher conductance states. The DFT simulations reveal the transmission eigenstate of geometrically optimized atomic point contact structures and the impact of the atomic configurations and structural stability on the conductance state, which also explains their resistive switching behaviors. The well‐defined, multiple quantized conductance states observed in these polymer‐based atomic switches show promise for the development of new multilevel memory devices.

Magnetic Conductive Filament Formed in the ReRAM Device with Ferromagnetic Electrode

We studied magnetic conduction property of the conductive filament formed in the ReRAM device having two ferromagnetic electrodes. Anisotropic Magnetoresistance (AMR) property was observed in the ON-state of the devices, however, negative MR occurred for the one device and positive MR occurred for another devices. There were abrupt change of resistance around 250 mT for these devices. Micromagnetic simulation study strongly suggested that the abrupt change of MR was caused by the single domain switching of the magnetic conductive filament (MCF). Furthermore, it is suggested that typical MCF size was 40 x 40 x 4 nm3 by assuming that MCF was composed of Ni metals. It is also suggested that the difference of negative AMR and positive AMR is derived from the location of MCF. The present results suggest a possibility of new multilevel memory devices which can be operated by both electric field as well as magnetic field.

A novel ternary memory property achieved through rational introduction of end-capping naphthalimide acceptors

Small molecule-based multilevel rewritable memory devices have gained attention because they possess super-high storage density, can sustain the stored data without power supply and erase/rewrite electrically; however, formation of these memory devices is extremely hard to achieve.

Graphdiyne for multilevel flexible organic resistive random access memory devices

A novel carbon material graphdiyne and thermally deposited Al–Al2O3core–shell NPs were employed to realize flexible multilevel RRAM.

Single Event Upsets Induced by Direct Ionization from Low-Energy Protons in Floating Gate Cells

Floating gate cells in advanced NAND Flash memories, with single-level and multi-level cell architecture, were exposed to low-energy proton beams. The first experimental evidence of single event upsets by proton direct ionization in floating gate cells is reported. The dependence of the error rate versus proton energy is analyzed in a wide energy range. Proton direct ionization events are studied and energy loss in the overlayers is discussed. The threshold LET for floating gate errors in multi-level and single-level cell devices is modeled and technology scaling trends are analyzed, also discussing the impact of the particle track size.

Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures

Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroic heterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.

Multilevel Resistive-Change Memory Operation of Al-Doped ZnO Thin-Film Transistor

A multilevel resistive-change memory device with thin-film transistor (TFT) structure is proposed, in which both functions of transistor and nonvolatile memory can be performed. Al-doped ZnO was employed for the active channel of the TFT as well as for the resistive-change material of the memory device. Multilevel memory operations could be realized by controlling the number of conducting filaments within the channel. Sound TFT characteristics and nonvolatile memory functions were demonstrated. The programmed current ratios for three-level memory states were 1:3.8:25. As results, long-time stability ( $10^{4}$ s) and program endurance (100 cycles) for the three-level memory states were also confirmed.

Interdimensional optical isospectrality inspired by graph networks

A network picture has been applied to various physical and biological systems to understand their governing mechanisms intuitively. Utilizing discretization schemes, both electrical and optical materials can also be interpreted as abstract 'graph' networks composed of couplings (edges) between local elements (vertices), which define the correlation between material structures and wave flows. Nonetheless, the fertile structural degrees of freedom in graph theory have not been fully exploited in physics owing to the suppressed long-range interaction between far-off elements. Here, by exploiting the mathematical similarity between Hamiltonians in different dimensions, we propose the design of reduced-dimensional optical structures that perfectly preserve the level statistics of disordered graph networks with significant long-range coupling. We show that the disorder-induced removal of the level degeneracy in high-degree networks allows their isospectral projection to one-dimensional structures without any disconnection. This inter-dimensional isospectrality between high- and low-degree graph-like structures enables the ultimate simplification of broadband multilevel devices, from three- to one-dimensional structures.

Towards Highly-Efficient Phototriggered Data Storage by Utilizing a Diketopyrrolopyrrole-Based Photoelectronic Small Molecule.

A cooperative photoelectrical strategy is proposed for effectively modulating the performance of a multilevel data-storage device. By taking advantage of organic photoelectronic molecules as storage media, the fabricated device exhibited enhanced working parameters under the action of both optical and electrical inputs. In cooperation with UV light, the operating voltages of the memory device were decreased, which was beneficial for low energy consumption. Moreover, the ON/OFF current ratio was more tunable and facilitated high-resolution multilevel storage. Compared with previous methods that focused on tuning the storage media, this study provides an easy approach for optimizing organic devices through multiple physical channels. More importantly, this method holds promise for integrating multiple functionalities into high-density data-storage devices.

A Memristive Pascaline

The original Pascaline was a mechanical calculator able to sum and subtract integers. It encodes information in the angles of mechanical wheels and through a set of gears, and aided by gravity, could perform the calculations. Here, we show that such a concept can be realized in electronics using memory elements such as memristive systems. By using memristive emulators we have demonstrated experimentally the memcomputing version of the mechanical Pascaline, capable of processing and storing the numerical results in the multiple levels of each memristive element. Our result is the first experimental demonstration of multidigit arithmetics with multi-level memory devices that further emphasizes the versatility and potential of memristive systems for future massively-parallel high-density computing architectures.

Multilevel Nonvolatile Memristive and Memcapacitive Switching in Stacked Graphene Sheets.

We fabricated devices consisting of single and double graphene sheets embedded in organic polymer layers. These devices had binary and ternary nonvolatile resistive switching behaviors, respectively. Capacitance-voltage (C-V) curves and scanning capacitance microscopy (SCM) images were obtained to investigate the switching mechanism. The C-V curves exhibited a large hysteresis, implying that the graphene sheets acted as charging and discharging layers and that resistive switching was caused by charges trapped in the graphene layers. In addition, binary capacitive switching behaviors were observed for the device with a single graphene sheet, and ternary capacitive switching behaviors were observed for the device with the double graphene sheets. These results demonstrated that devices consisting of graphene sheets embedded in the polymer layers can be applied to multilevel nonvolatile memcapacitive devices as well as memristive devices.

A Phosphole Oxide-Containing Organogold(III) Complex for Solution-Processable Resistive Memory Devices with Ternary Memory Performances.

A novel class of luminescent phosphole oxide-containing alkynylgold(III) complex has been synthesized, characterized, and applied as active material in the fabrication of solution-processable resistive memory devices. Incorporation of the phosphole oxide moiety in gold(III) system has been demonstrated to provide an extra charge-trapping site, giving rise to intriguing ternary memory performances with distinct and low switching threshold voltages, high OFF/ON1/ON2 current ratio of 1/10(3)/10(7), and long retention time for the three states. The present study offers vital insights for the future development of multilevel memory devices using small-molecule organometallic compounds.