Good Retention Characteristics Research Articles

Memristive switching in the surface of a charge–density–wave topological semimetal

Owing to the outstanding properties provided by nontrivial band topology, topological phases of matter are considered as a promising platform towards low–dissipation electronics, efficient spin–charge conversion, and topological quantum computation. Achieving ferroelectricity in topological materials enables the non–volatile control of the quantum states, which could greatly facilitate topological electronic research. However, ferroelectricity is generally incompatible with systems featuring metallicity due to the screening effect of free carriers. In this study, we report the observation of memristive switching based on the ferroelectric surface state of a topological semimetal (TaSe4)2I. We find that the surface state of (TaSe4)2I presents out–of–plane ferroelectric polarization due to surface reconstruction. With the combination of ferroelectric surface and charge–density–wave–gapped bulk states, an electric–switchable barrier height can be achieved in (TaSe4)2I–metal contact. By employing a multi–terminal–grounding design, we manage to construct a prototype ferroelectric memristor based on (TaSe4)2I with on/off ratio up to 103, endurance over 103 cycles, and good retention characteristics. The origin of the ferroelectric surface state is further investigated by first–principles calculations, which reveals an interplay between ferroelectricity and band topology. The emergence of ferroelectricity in (TaSe4)2I not only demonstrates it as a rare but essential case of ferroelectric topological materials, but also opens new routes towards the implementation of topological materials in functional electronic devices.

Experiment for the performance of a thin membrane inclined automatic wicking dew-point evaporative cooling device based on simulation results

The traditional indirect evaporative coolers necessitate a continuous operation of water pumps to ensure the wetting of wet channel walls. However, excessive water spraying can lead to a thickened water film, negatively impacting heat transfer efficiency and generating an additional pressure drop. Identifying suitable water supply strategies and exploring materials for the wet channel that possess good moisture retention and evaporation characteristics has drawn research attention over the years.In this study, an automatic wicking dew-point evaporative cooling device, whose structure was determined by corresponding optimal performance simulation research, was designed and manufactured. The thin film exhibits a certain inclination angle between the dry and wet channels to form a triangular channel to enhance support and increase heat transfer area. Utilizing the automatic water absorption characteristics of the membrane for water supply instead of spraying, makes the water more uniform and heat exchange more efficient. A comprehensive study was conducted on the effects of different operating parameters (working-to-intake air ratio, intake air velocity, water temperature, intake air temperature, and intake air humidity) on the performance of the device. The results indicate that the cooler performs best in high-temperature, low-humidity environments. When the inlet temperature, humidity, and velocity are within the range of 25–45 °C, 20–80 %, and 0.5–2.5 m/s, respectively, with a water temperature of 22 °C and an air-to-water flow rate ratio of 0.5, the maximum temperature drop can reach 14.8 °C, and the cooling capacity per unit area ranges from 13 to 150 W/m2. The wet-bulb efficiency and dew-point efficiency increased from 52.4 % and 33.6 % to 110.6 % and 88.5 %, respectively. When the air velocity increases from 0.5 m/s to 2.5 m/s, the product air temperature increases by 3.1 °C, and the wet-bulb efficiency and dew-point efficiency decrease by 25.1 % and 17.5 %, respectively. However, the variation trends of unit area cooling capacity and energy efficiency ratio (EER) are opposite. The optimal operating conditions are proposed with an air volume ratio of 0.5 and a water temperature range of 22–26 °C. Finally, the temperatures of the product air and water were observed during long-term operation testing to evaluate the stability of the device.

MOF-enabled high-density 2D molecular crystal optoelectronic memory transistor with floating gate architecture

A novel MOF floating-gate optical memory transistor was engineered using 2D molecular crystals as the active layer, and it exhibited an excellent electron capture ability, good current retention characteristics, and multi-level memory functionalities.

Analog memristive devices based on La2NiO4+ δ as synapses for spiking neural networks

Neuromorphic computing has recently emerged as a potential alternative to the conventional von Neumann computer paradigm, which is inherently limited due to its architectural bottleneck. Thus, new artificial components and architectures for brain-inspired computing hardware implementation are required. Bipolar analog memristive devices, whose resistance (or conductance) can be continuously tuned (as a synaptic weight), are potential candidates for artificial synapse applications. In this work, lanthanum nickelate (La2NiO4+δ , L2NO4), a mixed ionic electronic conducting oxide, is used in combination with TiN and Pt electrodes. The TiN/L2NO4/Pt devices show bipolar resistive switching with gradual transitions both for the SET and RESET processes. The resistance (conductance) can be gradually modulated by the pulse amplitude and duration, showing good data retention characteristics. A linear relationship between the resistance change and total applied pulse duration is experimentally measured. Moreover, synaptic depression and potentiation characteristics, one of the important functions of bio-synapses, are artificially reproduced for these devices, then modeled and successfully tested in a spiking neural network environment. These results indicate the suitability of using TiN/L2NO4/Pt memristive devices as long-term artificial synapses in neuromorphic computing.

Effects of Mg Doping to a LiCoO2 Channel on the Synaptic Plasticity of Li Ion-Gated Transistors.

Artificial synapses with ideal functionalities are essential in hardware neural networks to allow for energy-efficient analog computing. However, the realization of linear and symmetric weight updates in real synaptic devices has proven challenging and ultimately limits the online training capabilities of neural network systems. Herein, we investigate the effect of Mg doping on a LiCoO2 (LCO) channel in a Li ion-gated synaptic transistor, so as to improve long-term and short-term plasticity. Two transistor structures, based on a lithium phosphorus oxynitride electrolyte, were examined by using undoped LCO and Mg-doped LCO as the channel material between the source and drain electrodes. It was found that Mg doping increased the initial channel conductance by 3 orders of magnitude, which is probably due to the substitution of Co3+ by Mg2+ and the compensation of hole creation. It was further found that the doped channel transistor showed good retention characteristics and better linearity of long-term potentiation and depression when voltage pulses were applied to the gate electrode. The improved retention and linearity are attributed to an extended range of the insulator-to-conductor transition by Mg doping and Li-ion extraction/insertion cooperated in the LCO channel. Using the obtained synaptic weight update, artificial neural network simulations demonstrated that the doped channel transistor shows an image recognition accuracy of ∼80% for handwritten digits, which is higher than ∼65% exhibited by the undoped channel transistor. Mg doping also improved short-term plasticity such as paired-pulse facilitation/depression and Hebbian spike timing-dependent plasticity. These results indicate that elemental doping to the channel of Li ion-gated synaptic transistors could be a useful procedure for realizing robust neuromorphic systems based on analog computing.

Liposomal Doxorubicin: the Sphingomyelin/Cholesterol System Significantly Enhances the Antitumor Efficacy of Doxorubicin

Doxorubicin (DOX) has a cytotoxic effect on many tumor cells; however, its clinical application is limited owing to its strong side effects. Although Doxil® reduces the cardiotoxicity of free DOX, it has also introduced a new dose-limiting toxicity. In a previous study, a sialic acid-cholesterol conjugate (SA-CH) was synthesized and modified onto the surface of DOX-loaded liposomes to target tumor-associated macrophages (TAMs), further improving the efficacy of DOX-loaded liposomes over that of Doxil®. Meanwhile, the good retention characteristics and promising antitumor ability of sphingomyelin/cholesterol (SM/CH) system for water-soluble drugs have attracted wide attention. Therefore, we aimed to use SA-CH as the target and hydrogenated soybean phosphatidylcholine (HSPC) or egg sphingomyelin (ESM) as the membrane material to develop a more stable DOX-loaded liposome with stronger antitumor activity. The liposomes were evaluated for particle size, polydispersity index, zeta potential, entrapment efficiency, in vitro release, long-term storage, cytotoxicity, cellular uptake, pharmacokinetics, tumor targetability, and in vivo antitumor activity. In the liposomes prepared using HSPC/CH, sialic acid (SA) modification considerably increased the accumulation of DOX-loaded liposomes in the tumor, thus exerting a better antitumor effect. However, SA modification in DOX-ESL (SA-CH-modified DOX-loaded liposomes prepared by ESM/CH) destroyed the strong retention effect of the ESM/CH system on DOX, resulting in a reduced antitumor effect. Notably, DOX-ECL (DOX-loaded liposome prepared by ESM/CH) had the optimal storage stability, lowest toxicity, and optimal antitumor effect due to better drug retention properties. Thus, the ESM/CH liposome of DOX is a potential drug delivery system. Sketch of the effect of two DOX-loaded liposomes with hydrogenated soybean phospholipid (HSPC) and egg sphingomyelin (ESM) as lipid membrane material and surface-modified SA derivative on tumor growth inhibition.

Особенности получения и применения мицеллярного казеина в технологии молокоемких белковых продуктов

The modern food industry sees raw milk as a source of functional ingredients. Technologies of protein ingredients have a great scientific and practical importance because membrane fractionation methods preserve the native structure and properties of protein components. The resulting proteins have good fat profile, moisture retention, and emulsification characteristics, as well as perform some useful technological functions in food systems. They have no status of food additives and can be applied in various branches of food production. Unfortunately, the Russian food industry has no such technologies of its own. This article introduces some technological recommendations for the p roduction of domestic micellar casein concentrate.
 The research involved skim milk, commercial micellar casein concentrates from various manufacturers, curd samples with 9.0% of fat in dry matter, and Rossiysky cheese produced according to traditional formulation and technology. The experiment relied on standard research methods of physical and chemical analysis to establish the chemical composition of the samples, e.g., fractional composition of skim milk proteins, grain-size distribution, amino acid profile, etc.
 The study involved a comparative analysis of the chemical composition, as well as functional and technological properties of commercial micellar casein concentrates from various manufacturers. A set of experiments made it possible to define the thermal effect on raw material and to predict the prospects for usage of the new technology. Samples with a high ratio of casein:whey proteins and a moderately high heat treatment increased the curd and cheese yield by 10–12% in comparison with the traditional formulation. Samples with the maximal concentration of undenatured milk-serum protein nitrogen increased the yield of protein dairy products by 2–3% in comparison with other samples of micellar casein concentrates. The ratio of casein:whey proteins was 80:20 in skim milk obtained at PJSC Dairy “Voronezhsky”. The optimal pore diameter was ≥ 15 nm. As for the microbiological properties, QMA&OAMO was 6×104 CFU/dm3, and no pathogenic microorganisms were detected.
 Therefore, low-temperature pasteurization proved feasible at ≤ 76 ± 2°C and 10–15 s of hold time. The micellar casein concentrate added certain functional and technological properties to the finished product, depending on the specific application scope. 
 The new technology will enable the domestic food industry to ov ercome the existing import dependence.

Enhanced resistive switching properties of HfAlOx/ZrO2- based RRAM devices

Resistive Random-Access Memory (RRAM) devices are recognized as potential candidates for next-generation memory devices, due to their smallest cell size, high write/erase speed, and endurance. Particularly, the resistive switching (RS) characteristics in oxide materials have offered new opportunities for developing CMOS-compatible high-density RRAM devices. In this study, the RS behavior of HfAlOx/ZrO2 thin films sandwiched structure between TiN bottom electrode and Au top electrodes were investigated. It was found that Au/HfAlOx/ZrO2/TiN stacks were superior in terms of RS performance when compare to Au/HfAlOx/TiN memory stacks. The devices demonstrated a good resistance ratio of high resistance state and low resistance state ∼103 for Au/HfAlOx/TiN and ∼105 for Au/HfAlOx/ZrO2/TiN stacks, respectively. Both stacks showed good retention characteristics (>104 ​s) and endurance (>103 cycles). The experimental current-voltage characteristics fitted with different conducting mechanisms, the linear lower bias region is dominated by ohmic conductivity, whereas the non-linear higher bias region was dominated by space-charge limited current conduction mechanism.

Pulse optimization and device engineering of 3D charge-trap flash for synaptic operation

We investigate 3D charge-trap (CT) nand flash cells using device-physics based multi-scale simulations to explore their potential and optimum operating conditions as electronic synapses of the neuromorphic hardware. A set of figure of merits (FOMs) has been adopted to indicate their goodness of operation under incremental pulse inputs. The results of this study suggest that excellent synaptic FOMs can be attained from 3D CT nands by designing and calibrating the input pulse trains. The impact of variations of device dimensions on charge capture and release phenomena have been investigated and linked to output characteristics in order to obtain intuitive guidelines for attaining desired synaptic functionalities. By co-designing gate dielectric stack and input pulses, the threshold voltage (VT) of the 3D CT cell can be sequentially increased and decreased in a linear and symmetric fashion, providing a large number of distinct VT levels with good retention characteristics. Statistical simulations suggest that device-to-device variations of electrical responses have a negligible impact on the synaptic capabilities of these devices. It has also been shown that the incorporation of deeper traps through material engineering improves synaptic reliability of the 3D CT cells under prolonged operations.

Tunable Volatile to Non‐Volatile Resistive Switching in PbZrO3 Antiferroelectric Thin Film for Neuromorphic Computing

AbstractA direct coupling of antiferroelectric (AFE) and resistive switching (RS) is realized for the first time in an oxide heterostructures (non‐tunneling mechanisms). This allows the resistance of the heterostructure to switch between volatile and non‐volatile RS behavior, which indicates a threshold RS and broadly increases its practical applicability. The stacks of Pt/PbZrO3 (PZO)/LaNiO3/SrTiO3 (STO) is fabricated by laser pulse deposition. It exhibits a tunable RS behavior from volatile to nonvolatile through adjusting voltage amplitude. Moreover, a high ON/OFF ratio, good retention, and endurance characteristics are achieved. Furthermore, synaptic behaviors related to neural learning functions in PZO film is explored, that is, long‐term potential/depression, spike timing dependent plasticity, and paired pulse facilitation. This work provides a way to engineer AFE and RS pertinent functionality for the low‐energy‐consumption, non‐volatile neural computing.

Effect of TiW blocking layer and temperature annealing on resistive switching parameters of Hafnium oxide based CBRAM device

An approach for enhancing the characteristics of resistive switching in the crystalline Hafnium oxide-based CBRAM (Conductive Bridging Resistive Switching Memory) device is reported in this article. The crystalline Hafnium oxide resistive switching layer and the TiW blocking layer are beneficial for controlling filament growth. Improved resistive parameters, including stability and resistance distribution, were successfully demonstrated in Cu/TiW/annealed-HfO2/Pt devices compared to Cu/HfO2/Pt-based devices. Moreover, the proposed bipolar device demonstrates improved memory performance, such as good retention characteristics (>104 s) and a high ON/OFF resistance ratio.

Large memory window with low operating voltages using Hf 1.5 Gd 2 O 6 charge trapping layer and thin MoS 2 channel

A charge-trapping memory (CTM) field effect transistor (FET) featured with an Hf1.5Gd2O6 charge trapping layer and thin MoS2 channel are fabricated. Benefit from high defect densities of the Hf1.5Gd2O6 film, large memory windows are achieved under low operating voltages (2.3 V@4 V, 3.1 V@5 V and 3.6 V@6 V), which distinctly outperform previously reported CTMs. In addition, high programming/erase (P/E) speeds, good data retention and endurance characteristics are experimentally demonstrated. The results demonstrate a feasibility of CTM FET with an HfGdO charge trapping layer and thin MoS2 channel for ultra-low power memory devices application.

Improvement of Resistive Switching Performance in Sulfur-Doped HfOx-Based RRAM.

In order to improve the electrical performance of resistive random access memory (RRAM), sulfur (S)-doping technology for HfOx-based RRAM is systematically investigated in this paper. HfOx films with different S-doping contents are achieved by atmospheric pressure chemical vapor deposition (APCVD) under a series of preparation temperatures. The effect of S on crystallinity, surface topography, element composition of HfOx thin films and resistive switching (RS) performance of HfOx-based devices are discussed. Compared with an undoped device, the VSET/VRESET of the S-doped device with optimal S content (~1.66 At.%) is reduced, and the compliance current (Icc) is limited from 1 mA to 100 μA. Moreover, it also has high uniformity of resistance and voltage, stable endurance, good retention characteristics, fast response speed (SET 6.25 μs/RESET 7.50 μs) and low energy consumption (SET 9.08 nJ/RESET 6.72 nJ). Based on X-ray photoelectron spectroscopy (XPS) data and fitting of the high/low resistance state (HRS/LRS) conduction behavior, a switching mechanism is considered to explain the formation and rupture of conductive filaments (CFs) composed of oxygen vacancies in undoped and S-doped HfOx-based devices. Doping by sulfur is proposed to introduce the appropriate concentration oxygen vacancies into HfOx film and suppress the random formation of CFs in HfOx-based device, and thus improve the performance of the TiN/HfOx/ITO device.

Solidification/stabilization of copper-contaminated soil using phosphogypsum

Heavy metal contamination has become a major environmental concern worldwide. On the other hand, more than 300 million tons of annual worldwide production of phosphogypsum is leading to disposal and environmental problems. In view of this, an effort has been made in this investigation to evaluate the effectiveness of phosphogypsum-based stabilization/solidification technique to remediate copper-contaminated soil. Two concentrations of copper (630 mg/kg and 20,000 mg/kg) were selected on the basis of literature and were used to synthetically prepare the contaminated soils. A systematic testing program consisted of consistency limits, compaction, unconfined compressive strength, cation exchange capacity, X-ray diffraction, and scanning electron microscopy with EDAX was conducted on phosphogypsum-treated uncontaminated and contaminated soils. The UCS test results showed that 3% phosphogypsum was optimal for uncontaminated soil, which was used to treat the contaminated soils. An increase in strength was observed in uncontaminated soil with lower phosphogypsum content at all curing periods (3, 7, 14 and 28 days). Formation of copper sulfate-based minerals with good retention and diminutive leaching characteristics of copper in soil indicates the effectiveness of PG. Overall, phosphogypsum can be employed for effective treatment of copper-contaminated soils.

Nanocomposite hydroxide for resistive switching memory devices and the effect of adsorbed small molecule hexazinone

The nonvolatile resistive switching memory devices and the effect of adsorbed small molecule hexazinone have been investigated. Resistive switching behaviour of Co-Al layered double hydroxides (Co-Al LDHs)-based is gradually varied. At the same time, when Co-Al LDHs adsorbed the small molecule hexazinone, its resistive switching behaviour changed suddenly. Both memristors exhibit non-volatile data storage and good data retention characteristics. The influence of small molecule hexazinone on microcarrier transport was analyzed. This research manifests the promising potential of nanocomposite materials adsorbed electroactive small molecules in rectifying the resistive switching properties and provides some ideas for designing advanced devices of nanocomposite memristors.

Mechanism of analog bipolar resistive switching and work function in Au/Na0.5Bi0.5TiO3/Pt heterostructure thin films

We report on the room temperature work function value of Na0.5Bi0.5TiO3 (NBT) thin films and bias dependent analog bipolar resistive switching characteristics in Au/Na0.5Bi0.5TiO3/Pt thin film hetero-structure. Na0.5Bi0.5TiO3 thin films crystallize in rhombohedral (R3c) structure, confirmed from the Raman and X-ray diffraction studies. Scanning electron microscope images indicates that the surface morphology is smooth and films grown in rod-like structure vertically. Oxidation states of Na, Bi and Ti elements are confirmed from the X-ray photoelectron spectroscopy technique. The device retains its bipolar switching behavior in direct current (dc) sweeping mode by an applied voltage of ±3 V, without any deterioration suggests good retention characteristics. The ON/OFF resistance ratio (RON/ROFF) between high and low resistance states is of the order of 10. The role of oxygen vacancies and charge transport process in low resistance state (LRS) and high resistance states (HRS) are examined using Ohmic and space-charge-limited conduction mechanisms. The current-voltage (I–V) characteristics show space-charge-limited conduction dominates at high electric fields. The average work function value of the Na0.5Bi0.5TiO3thin film at room temperature is found to be 5.09 eV. The interface interactions of Au/NBT and NBT/Pt thin layers and their role in initiating resistive switching is discussed in detailed.

Reliable restriction of conductive filament in graphene oxide based RRAM devices enabled by a locally graphitized amorphous carbon layer

In this work, a locally graphitized amorphous carbon (LGAC) film was successfully prepared through catalytic graphitization process. Taking advantage of its locally conductive characteristic, we demonstrate an effective and repeatable method to improve the reliability of graphene oxide based RRAM devices. The above method is responsible for a fluctuation decrease of high/low resistance states (HRS/LRS) and SET/RESET voltage from 139.6%/76.9% to 31.4%/7.5% and 50.5%/47.7% to 7.7%/6.9%, respectively. The migration of oxygen ions during both the SET and RESET processes were well restrained within the narrow conductive areas thanks to the LGAC insertion layer. In addition, the optimized memory devices also showed pretty good cycling endurance and high temperature retention characteristics. This approach may be promising for developing reliable graphene oxide based RRAM devices.

Light-sensitive charge storage medium with spironaphthooxazine molecule-polymer blends for dual-functional organic phototransistor memory

Abstract Organic phototransistor memory is considered as a promising optoelectronic device owing to its multifunctionality. However, due to the poor reliability of each function and the complexity of the device structure, it is necessary to optimize the thin-film process of functional materials when constructing multiple functions into a single device. Here, we demonstrate a dual-functional device that is both a working memory transistor and a phototransistor by incorporating photochromic spironaphthooxazine molecules into an organic insulating layer. The photochromic molecules in the polymer matrix not only exhibit nonvolatile charge storage properties similar to nano-floating gates but also feature a reversible electronic band structure upon alternating irradiation with ultraviolet and visible light, which makes the device function as both an electrical memory transistor and a phototransistor. Furthermore, the photoresponsive charge trap layer in the demonstrated device leads to excellent memory performance under both dark and light conditions, which includes a large memory window (~56 V), stable endurance cycles (>102), and good retention characteristics (>104 s). Our findings suggest an alternative strategy to realize organic multifunctional nonvolatile memories.

Multi-valued charge trapping memory based on amorphous-indium-gallium-zinc oxide thin film transistor with designed Ga2O3/Al2O3 stack insulator

Multi-valued charge trapping memory is demonstrated based on an amorphous-indium-gallium-zinc oxide thin-film transistor (a-IGZO-TFT) with a Ga2O3/Al2O3 stack gate insulator. The memory device shows a positive shift of threshold voltage as large as 12.6 V after +20 V/1 s programming. The erasing process can be divided into two stages. Vertical electrical field erases the trapped electrons partially, resulting in negative threshold voltage shift with hump current in sub-threshold region. It is defined as a first erasing stage. Furthermore, the memory can be erased by UV-light effectively due to the generated electron-hole pairs in a-IGZO channel. It is defined as second erasing stage. The good retention characteristics are confirmed for various storage states. The storage mechanism is analyzed according to the energy band alignment obtained by XPS narrow scans and valence band spectra.

A Study on the Charge Trapping Characteristics of High-k Laminated Traps

The charge trapping characteristics of the high-k laminated traps with different thickness ratios were investigated in order to improve the distribution of threshold voltage and the charge loss problems in 3D NAND flash memories with TCAT structure. In this letter, the interfacial layers are formed between the HfO2/Al2O3 laminated films, which increase trap sites and improve charge storage capability. In addition, due to the difference in bandgap between HfO2 and Al2O3, the HfO2 layer forms a deep quantum well and the Al2O3 layer acts as a barrier to prevent the loss of electrons captured in the charge trapping layer. The barriers prevent trapped electrons from escaping to other layers. In other words, it reduces the loss of charges from the charge trapping layer to Si or gate electrode. Also, the number of interfaces and the ratio of appropriate laminate film thickness are important factors for obtaining good data retention characteristics. The experimental results show a higher charge storage density and a larger memory window of 11.5 V in the structure that has many interfaces and a 1/1 of HfO2/Al2O3 thickness ratio. In this structure, the leakage current is 4.61 $\times$ 10−9A/cm2 and charge loss rate is 14.9%, which are the lowest values in tested structures. The proposed high-k laminated trap structure may be very useful in future 3D NAND flash memory device applications.