Voltage Sweep Research Articles

Sol–gel derived BST (BaxSr1−xTiO3) thin film ferroelectrics for non-volatile memory application with metal–ferroelectric–semiconductor (MFS) structure

Thin film of Barium–Strontium–Titanate (BaxSr1−xTiO3) has been fabricated through sol–gel spin-coating process with optimized value of ‘x’ for non-volatile memory application. The Metal–Ferroelectric–Semiconductor (MFS) thin-film structures have been prepared using Barium–Strontium–Titanate (BST) with various Barium/Strontium (Ba/Sr) molar concentrations. The BST films prepared through sol–gel process are annealed at 650 °C in nitrogen ambient. The structural and electrical characterizations have been carried out for each of the samples. From the characterization, it is realized that the BST films are having significant changes in its electrical and structural properties on changing the molar concentration of Barium and Strontium. It has been observed that the crystallinity of the film, refractive index, leakage current (I−V), capacitance vs. voltage (C−V) relation, and the charge vs. voltage (Q–V) relation vary with the varying values of ‘x’ in BaxSr1−xTiO3 and have been presented graphically. The maximum memory window up to 9 V with average leakage current within the range of 100 nA and minimum of 10 pA for 0 V has been achieved for the sweep voltage of + 15 V to -15 V. Memory window and leakage current are optimized and discussed. Endurance testing through PUND (positive up negative down) pulse shows that the samples can sustain up to 1010 iteration pulses. These findings indicate the use of optimized BST film for ferroelectric non-volatile memory applications through sol–gel process.

Nonlinear Electric Field Dependence of the Transverse Piezoelectric Response in a Ferroelectric Film

A non-linearly decreasing piezoelectric coefficient with an external electric field is an intrinsic property of a fully poled ferroelectric film, which has been observed in the measured longitudinal piezoelectric responses. However, for transverse piezoelectric responses, the observed converse piezoelectric coefficients (e31,f) have displayed a different trend. Here we show that this disagreement can be rationally resolved by utilizing a small field e31,f test under a sweeping direct current bias voltage, in which the field-dependent transverse piezoelectric response is analyzed in a stepwise manner. Understanding of this nonlinear field-dependence will help improve the design of transverse piezoelectric devices.

2H-MoS2 nanoflowers with exposed edges for hydrogen producing electrochemical cell

In this study, we report hexagonal MoS2 nanoflowers with well exposed edges as efficient catalyst for hydrogen production. The 2H-MoS2 nanoflowers based electrodes show a low overpotential of 0.193 V and a Tafel slope of 69 mV dec1 at a voltage sweep rate of 5 mV s−1 for hydrogen evolution reaction with excellent stability for more than 2500 cycle. We also demonstrate the production and collection of hydrogen using in-house developed electrochemical cell with 2H-MoS2 nanoflowers as cathode.

Influence of the rapid thermal treatment of the gate dielectric on the parameters of integrated circuits of time devices

The paper is dedicated to influence of the rapid thermal treatment of the gate dielectric at a temperature of ~1100 ° С on the electrical parameters of the programmable time device with a correction of 512PS8. As the analyzed parameters of the given integrated circuit, the authors have selected breakdown voltage, gate leakage current, charge value of the gate dielectric breakdown with its thermal field tests performed. The breakdown voltage of the p -channel of the test transistor was measured by applying the linear voltage sweep from 0 to -100 V with the step of -0,5 V with the grounded drain and source. The leakage current of the gate Ig leak was determined at the gate voltage of -20 V. For evaluation of the charge properties of the gate dielectric of devices the, the thermal field tests were performed. The quality and reliability of the gate dielectric the authors the breakdown charge control was carried out ( Q bd ). It is shown that the rapid thermal treatment of the gate dielectric at a temperature of ~1100 ° С during 7 s with its presence on the non-working side ensures the breakdown charge value of 2,040 C/cm 2 , and with its absence - 2,230 C/cm 2 , while during the standard process of creating the given integrated circuit this value constitutes 1,230 C/cm 2 . This means that the most efficient influence on the improvement of quality and reliability of the gate dielectric is ensured by its rapid thermal treatment when missing the silicon dioxide on the non-working side of the wafer. As compared with the standard process of their fabrication, carrying out such treatment allows 5,29 times reduction of the gate leakage current, 3,50 times reduction of the charge states and 1,07 times enhancement of the reliability of the p -channel transistor, and for the n -channel transistor the given values constitute 10,67, 3,50 and 1,81 times, respectively. It is established that the reliability improvement for the CMOS integrated circuits of time devices during the rapid thermal treatment of the gate dielectric is determined by a step-up of its breakdown charge owing to the more perfect microstructure of dielectric, resulting in the rebuild of the charge states both in the bulk and on the boundary with silicon.

Fabrication of GaOx based crossbar array memristive devices and their resistive switching properties

Memristive devices attract much attention for the application to neuromorphic computing. Here we focus on amorphous GaOx based memristive devices and their integration as a crossbar architecture which is mandatory to improve parallelism in computing and essential to future power-saving, high-speed and reliable artificial neural networks (ANN). Fabricated Pt/GaOx/ITO crossbar array memristive devices with 3 × 3 μm2 crosspoints exhibit non-filamentary reversible bipolar resistive switching (RS) without any electroforming processes. We demonstrate the gradual resistance change by repeating voltage sweep and applying pulse voltages. The expression of spike-timing-dependent plasticity property, one of synaptic functions in neuromorphic devices, is also successful in the present device. The obtained results strongly suggest that the drift of oxygen vacancies in GaOx plays an important role in the RS behavior and the GaOx based crossbar array memristive devices have a great potential for hardware implementation of ANN.

Double Swing Quiescent-Current: An Experimental Detection Method of Ferroelectricity in Very Leaky Dielectric Films

Ferroelectric materials are very attractive for many technological applications. In the scenario of conventional CMOS technology, they are very suitable to fabricate nonvolatile memories (FeRAM) or as the gate stack of a transistor to realize a FeFET. Conventional ferroelectric materials, like PZT or SBT, exhibit very high permittivity and low coercive field and very thick films must be grown to obtain wide enough memory windows. Because of that, new ferroelectric materials must be investigated.Applications compatible with CMOS technology require very thin layers of dielectrics. Moreover, it is difficult to obtain new insulating materials with low conductivity in the early stages of their technological development. Therefore, ferroelectric properties can be masked by high leakage currents. This can result in the abandonment of these materials before the growing conditions are optimized. In addition, the conventional measurements of ferroelectric properties use techniques in which the electric field is varied with relatively high frequency signals that result in displacement currents that represent an additional term which is added to leakage currents and further conceals ferroelectric behavior. Traditional Sawyer-Tower techniques do not allow the detection of ferroelectricity when leakage and/or displacement currents are excessively important and even experimental values of polarization may be overestimated when affected by charge terms corresponding to the parasitic phenomena mentioned above.Basically, the double swing quiescent-current (DSQC) consists on measuring the current of the sample while varying the applied voltage as follows: a) To obtain the positive remanent polarization, we apply two identical voltage sweeps from zero to values high enough to polarize the sample. The swing rate is chosen slow enough to consider the measure process as a succession of quasi-stationary states. On the first sweep the current has three contributions: leakage, displacement and polarization itself. Since the material has already been polarized in the first sweep, the component due to ferroelectric polarization is no present in the second one. The difference between the curves of the first and second sweeps provide the curve due to the polarization current. b) Once the material is positively polarized, we repeat the same process but applying negative voltage sweeps to negatively polarize the material.To check the validity of the technique, we have performed previous tests with conventional ferroelectric materials. In Figures 1 and 2 we represent the current-voltage and charge-voltage characteristics obtained. We verify that the obtained results match the specifications for these materials.Afterwards, we have applied the DSQC method to characterize the ferroelectric behavior of amorphous SiO2-Nb2O5 nanolaminates and mixture films. The films were grown by atomic layer deposition. The films were grown at 300 oC from Nb(OC2H5)5, Si2(NHC2H5)6, and O3 to thicknesses ranging from 13 to 130 nm. The niobium to silicon atomic ratio was varied in the range of 0.11-7.20.In Figure 3 we observe a complete voltage current cycle. Starting from 0 V, the voltage increases linearly to a value of 12 volts and then decreases to -12 volts. Finally, the voltage returns to zero. A swing rate of 5 mV/s has been used to obtain this curve. In this figure you can observe the two peaks corresponding to the positive and negative polarization. It is also noted that the current is not zero when the sample is already polarized due to the existence of leakage and displacement currents.To remove these components two sweeps must be performed in each direction. In Figures 4 and 5 we present the result of applying double sweep for positive and negative voltages, respectively. The difference between the two sweeps provides the ferroelectric polarization current. We note that this current returns to zero once the sample has been polarized.In summary, we demonstrate that double swing quiescent-current technique allows to detect ferroelectric behavior even in highly conductive materials and obtain reliable values of the remaining polarization that are not affected by the parasitic effects of leakage and displacement currents. Figure 1

Understanding Fuel-Cell Impedance Spectra Via Numerical Modeling: A Single-Phase Water-Management Study

Cost of hydrogen-fueled proton-exchange-membrane fuel cells (PEMFCs) remains a challenge for the global commercialization of the technology and needs to be reduced to meet the U.S. Department of Energy goals [1]. Cost-reduction can be achieved by incorporating efficient water management, which helps keep the electrolyte hydrated while avoiding cell flooding by product water.Dynamic liquid-water accumulation and electrolyte hydration can be studied via transient polarization [2-6] and ohmic-resistance [2,4-7] curves, in which they induce hysteresis. Analyzing the polarization and resistance data may, however, be challenging due to the overlapping transients of various physical processes occurring in the cell during the voltage and current sweeps. Electrochemical impedance spectroscopy (EIS) allows the study of the dynamic processes of different time scales separately in the frequency domain and has been widely used for fuel-cell characterization [8-11].Fuel-cell impedance spectra often exhibit an inductive behavior at low frequencies, which has been shown to be affected by electrolyte hydration [10,12-14]. A recent experimental study [9] showed that the strength of this inductive behavior depends on the anode and cathode RH. Understanding the low-frequency inductance may help improve the water-management strategies for fuel cells. However, this inductive phenomenon has not been investigated in detail with a comprehensive numerical model.In this work, a transient 2D PEMFC model is developed in the open-source fuel-cell modeling software OpenFCST [17] with a thorough validation through dynamic polarization, resistance, and impedance-spectroscopy data at various operating conditions. Unlike other physical EIS models [13-16], the presented model does not rely on parameter fitting to reproduce the experimental impedance spectra. The model also takes the finite-rate water absorption/desorption kinetics of the electrolyte into account, which allows to investigate the effect of the interfacial transport of water on fuel-cell impedance and performance. With the presented model, water-management signatures are identified in fuel-cell impedance spectra under single-phase conditions that help elucidate electrolyte-hydration dynamics. The trends in the simulated effect of anode and cathode RH on the fuel-cell inductance are in agreement with experiments in [9], which verifies the model’s ability to correctly predict the inductive behavior. The low-frequency inductive behavior of fuel cells is shown to be related to the interfacial transport of water in the electrolyte and linked to the electrolyte-hydration and proton-conductivity dynamics in the membrane and in the catalyst layers. Additionally, an ohmic-resistance breakdown is performed with the model using the ohmic-heating-based approach proposed by Secanell et al. [18]. The high-frequency resistance obtained through EIS is shown to be comprised of the membrane resistance and the electronic resistance of other MEA components, but not the protonic resistance of the catalyst layers.Figure: Single-phase water-transport signatures in a fuel-cell-impedance spectrum.

Study of the Density of Interface States at the Insulator/In0.52Al0.48As Interface

The C–V characteristics of Au/Al2O3/In0.52Al0.48As and Au/SiO2/In0.52Al0.48As metal–insulator–semiconductor structures have been studied. It has been established that the fragmentary measurement of the C–V characteristics of InAlAs-based metal–insulator–semiconductor structures, in contrast standard registration method to at a constant voltage sweep rate, significantly weakens the effect of the hysteresis phenomena and allows one to record stationary curves. It is shown that the density of fast interface states calculated by the Terman method from such C–V characteristics slightly changes over the InAlAs band gap and amounts to (3–6) × 1011 and (1–3) × 1011 eV–1 cm–2 for MIS structures with Al2O3 and SiO2, respectively.

The Characterization of Nanofet Sensor with Extended Sensing Electrode and Reference Electrode for Biosensor Application

Biosensors based on nano field-effect transistor(nanoFET) have been studied to detect from pH to biomolecules and anion in the air because its potential for label-free detection, rapid response time, low-cost and miniaturization [1-3]. The nanoFET sensor detect target species with a conductance change of nanochannel that is induced by the adsorption of charged substance or the surface potential of the sensing gate electrode. However, the sensing area on top of the nanochannel area is very small, the probability of binding of target molecules on the sensing surface of the device is very low. Therefore, we employ an electrically extended sensing electrode in order to improve adsorption probability of the charged substances and detection sensitivity. Here, we analyzed the behavior of the nanoFET sensor with an extended gate electrode and a reference electrode using pH solution of difference pH levels. It is a fundamental study to understand the behavior of nanoFET sensor with extended gate as biosensors, and it is necessary before applying it to various solution environment.Figure 1 shows the schematics of the nanoFET sensor with the extended gate electrode for pH level sensing of solution. The top gate electrode and the bottom substrate gate of the nanoFET sensor are electrically interconnected with the extended external electrode in order to increase the sensing area. The Ids-Vg characteristics of the nanoFET sensor with extended gate electrode, which is obtained by the voltage sweeping of the gate (Vg) as shown in Figure 2. The threshold voltage of the device is approximately -2.5 V. The electrode of an indium tin oxide(ITO) glass and a Ag/AgCl wire are used for the extended sensing gate electrode and the reference electrode. The connection for gate electrode and the reference electrode are compared with three cases of ITO-Ag/AgCl, Ag/AgCl-ITO and ITO-ITO respectively to compare pH response with the Ids-Vg sweep characteristics of the nanoFET sensor. In the pH sensing experiment, about 50 μL-solution having 4, 7 and 9.2 pH level are used, and it is dropped to a micro well on the extended sensing gate electrode as shown in Figure 1. Figure 3 shows Ids-Vg measurement results of varying the pH level on solution for the three connection cases of extended sensing gate electrode and reference electrode using the same device. Figure 3(a) shows Ids-Vg curve is shifted to the right side as the pH level rises in case of the reference electrode is the Ag/AgCl wire and the extended sensing gate electrode is the ITO glass. The response to pH level is shifted to left side as shown in Figure 3(b) when the electrode connection is reversed for the reference electrode and the extended sensing gate electrode with the ITO glass and the Ag/AgCl wire, respectively. In particular, it is confirmed that the nanoFET device don’t respond to the pH change of solution when both the reference electrode and the extended sensing gate electrode are the ITO glass. We finally conclude that the nanoFET sensor with the extended sensing gate electrode is affected by the surface potential in electrolyte solution induced by varying pH level. The equivalent circuit model of the nanoFET sensor is the series interconnection of two opposing electrolytic capacitors and the MOS capacitor of nanoFET device to the applied gate voltage as shown in Figure 4. Therefore, the nanoFET sensor with the extended gate electrode may not respond to the pH change or ion concentration in electrolyte solution when the interface of liquid-reference electrode is equal to interface of liquid-sensing electrode.In this study, we demonstrated experimentally the working principles of the nanoFET sensor with the extended gate electrode with the response to pH level of liquid solution. We found that the equivalent circuit model is the series connection of two opposing electrolytic capacitors in liquid solution and the MOS capacitor of the nanoFET device. The results suggest that the proper reference electrode should be utilized to measure the pH levels in liquid solution of nanoFET sensor and the other adequate reference electrode might be used to remove the effects induced by pH noise for the biosensor application such as immunosensors.This work was financially supported by the research funds (Grant No. 10076874 and No. 10077599) of the Ministry of trade, Industry and Energy, Korea[1]Matti Kaisti, Detection principles of biological and chemical FET sensors, Biosensors and Bioelectronics, 98 (2017)[2]Benjamin M. Lowe et al. Field-effect sensors-from pH sensing to biosensing: sensitivity enhancement using streptavidin-biotin as a model system, Analyst 142 (2017)[3]K.-N. Lee et al. Chemical gating experiment of a nano-field-effect transistor sensor using the detection of negative ions in air, Sens. Actuators, B 236 (2016) Figure 1

Promising memristive behavior in MoS2–MoO2–MoO3 scalable composite thin films

Abstract Simple fabrication of materials with superior memristive behaviors is a key aspect of developing functional memristor devices. Partially oxidized MoS2 thin layers have been one of the most attractive candidates due to their promising memristive characteristics. However, its fabrication involves complicated multi-step methods. Here, we fabricate a thin film composed of MoS2, MoO2 and MoO3 elements (MoSO) with distinguishable memristive behaviors through electrodeposition technique. Both electrochemical metallization (ECM) and valence change (VCM) memristive responses observed with different top electrodes. By using Ag as the top electrode, the device shows ECM memristive behavior with low threshold voltages of ∼0.1–0.2 V, and on/off ratio of ∼200. Different VCM memristive behaviors at different voltage sweep intervals are observed in the case Au is used as the top electrode. The results indicate that the memristive behavior originates from the composite nature of the MoSO layer. An annealed MoSO layer in Ar and air, producing pure phases of MoS2 and MoO3, respectively, did not show memristive behavior. This simple one-step synthesis of the MoSO layer at room temperature with its possibility for scalable production may pave the way for development of functional memristors.

Understanding of Polarization-Induced Threshold Voltage Shift in Ferroelectric-Gated Field Effect Transistor for Neuromorphic Applications

A ferroelectric-gated fin-shaped field effect transistor (Fe-FinFET) is fabricated by connecting a Pb(Zr0.2Ti0.8)O3-based ferroelectric capacitor into the gate electrode of FinFET. The ferroelectric capacitor shows coercive voltages of approximately −1.5 V and 2.25 V. The polarization-induced threshold voltage shift in the Fe-FinFET is investigated by regulating the gate voltage sweep range. When the maximum positive gate to source voltage is varied from 4 V to 2 V with a fixed starting negative gate to source voltage, the threshold voltage during the backward sweep is increased from approximately −0.60 V to 1.04 V. In the case of starting negative gate to source voltage variation from −4 V to −0.5 V with a fixed maximum positive gate to source voltage of 4 V, the threshold voltage during the forward sweep is decreased from 1.66 V to 0.87 V. Those results can be elucidated with polarization domain states. Lastly, it is observed that the threshold voltage is mostly increased/decreased when the positive/negative gate voltage sweep range is smaller/larger than the positive/negative coercive voltage, respectively.

Comparative Analysis on Dielectric Gold and Aluminium Triangular Junctions: Impact of Ionic Strength and Background Electrolyte by pH Variations

Field of generating a surface thin film is emerging broadly in sensing applications to obtain the quick and fast results by forming the high-performance sensors. Incorporation of thin film technologies in sensor development for the better sensing could be a promising way to attain the current requirements. This work predominantly delineates the fabrication of the dielectric sensor using two different sensing materials (Gold and Aluminium). Conventional photolithography was carried out using silicon as a base material and the photo mask of the dielectric sensor was designed by AutoCAD software. The physical characterization of the fabricated sensor was done by Scanning Electron Microscope, Atomic Force Microscope, High Power Microscope and 3D-nano profiler. The electrical characterization was performed using Keithley 6487 picoammeter with a linear sweep voltage of 0 to 2 V at 0.01 V step voltage. By pH scouting, I-V measurements on the bare sensor were carried out, whereby the gold electrodes conducts a least current than aluminium dielectrodes. Comparative analysis with pH scouting reveals that gold electrode is suitable under varied ionic strengths and background electrolytes, whereas aluminium electrodes were affected by the extreme acid (pH 1) and alkali (pH 12) solutions.

Modelling the switching effect in graphene oxide-based memristors

The two-dimensionality of insulating graphene oxide sheets is attractive for use in nanoscale two-terminal devices. These structures are promising for the next generation of non-volatile resistive random access memories, with high speed, low-power consumption and excellent scalability. In this work, the transport properties of graphene oxide-based metal-insulator-metal structures are addressed. The graphene oxide was synthesized using an eco-friendly modified Hummers method. The obtained graphene oxide sheets, placed between two electrodes, were subjected to an electrical characterization measuring cycling current–voltage (I–V) curves by applying successive forward and reverse voltage sweeps. When the absolute value of the measured current is plotted in logarithmic scale versus the applied voltage, the typical butterfly-shaped curves are observed, which are better interpreted in terms of their first derivative, or differential conductivity, in order to understand the transport mechanism. The experimental I–V curves can be explained in two different ways: by modifying well-known transport models or by using typical flux-controlled memristor models. The connection between both strategies is established in this work. The analytical expressions used for the differential conductance for the low resistance state and the high resistance state lead to simple expressions for the I–V curves. The symmetry of the curves after several cycles is lost when compared to those measured on pristine devices, which might indicate the occurrence of filament forming effect, affecting the bipolar switching.

All‐Solid‐State Organic Schmitt Trigger Implemented by Twin Two‐in‐One Ferroelectric Memory Transistors

AbstractAlthough there have been many attempts to replace conventional inorganic electronics with organic materials that can be mass produced at low cost, few organic electronic filters to increase immunity to electrical noise have been reported thus far. Conventional Schmitt triggers or their inverters are used in many electronic circuits as versatile electronic noise filters. However, it is challenging to manufacture organic electronic systems with complex circuitry. In this study, a simple, all‐solid‐state organic Schmitt trigger consisting of twin two‐in‐one organic ferroelectric memory transistors with the same chemical compositions and device dimensions but different threshold voltages is introduced. Threshold voltages and hysteresis in the two‐in‐one devices can be controlled by polarization switching as demonstrated in a previous study. Hysteresis of a ferroelectric p‐type depletion load inverter can be achieved using twin two‐in‐one devices when the sweep voltage is higher than the critical gate voltages. This facilitates inverter characteristics at two different threshold voltages, and realizing a Schmitt trigger. Finally, based on simulation program with integrated circuit emphasis (SPICE) simulation, guidelines are proposed on how to design organic Schmitt triggers with p‐ or n‐type materials and ferroelectric or charge‐trapping mechanisms to achieve inverting or non‐inverting characteristics.

Employing defected monolayer MoS2 as charge storage materials

Recently, various two-dimensional (2D) materials have been employed in charge trapping memories as the charge trapping layer instead of conventional metal/semiconductor thin films or discrete particles. Such ultra-thin charge trapping layers are beneficial to the development of miniaturized devices, which is a trend in modern semiconductor technology. 2D MoS2 is an alternative charge trapping material, but previous investigations have been limited to their multilayers. Here, we present the study on employing monolayer MoS2 as charge trapping layer in charge trapping devices. We found that intrinsic monolayer MoS2 is less effective for charge trapping; while defective monolayer MoS2 shows enhanced charge storage capacity. By employing argon plasma treatments, we are able to control the defect density in monolayer MoS2 and the memory window of monolayer MoS2 based charge trapping devices can vary from 1.01 to 5.14 V at a sweeping voltage of ±20 V and program/erase slope from 0.06 to 0.32. Optimized devices show ∼1 ms program/erase speed, >70% charge retention after ∼7000 s and good endurance properties with >1000 cycles. The enhancement of the memory window is attributed to the localized charge tapping sites in defected monolayer MoS2. This work would provide insights for the improvement of storage capacity through defects engineering in the atomically thin 2D materials.

Initialization process of Cu-based WOx conductive bridge RAM investigated via in situ transmission electron microscopy

The initialization process of the Cu-WOx CBRAM was analyzed via in situ transmission electron microscopy (TEM). For the measurements, lateral-type devices were used to allow for clear microscopic observation. A widening of the electrode gap by electrochemical dissolution of the Cu anode during voltage application was experimentally confirmed. These results provide evidence for the chemical reaction occurring at the anode side of the CBRAM. The resistance gradually decreased after multiple voltage sweep applications, and deposits appeared and grew in the electrode gap region. Subsequently, sharp switching occurred, however, clear conductive filaments bridging the two electrodes were not detected within the resolution limit of the in situ TEM. Finally, a series of bipolar operations were realized; with continued bipolar operation, Cu accumulated in the switching region and device degradation occurred.

Enhanced memory characteristics of charge trapping memory by employing graphene oxide quantum dots

In this study, graphene oxide quantum dots (GOQDs) are embedded in the charge trapping layer of high-k material HfO2 for nonvolatile memory applications. The fabricated devices exhibit a large memory window of ∼1.57 V under a ±3.5 V applied sweeping voltage and show only ∼13.1% of charge loss after a retention time of 1.2 × 104 s. This excellent performance is attributed to the quantum well formed in the charge trapping layer. Defect traps in the HfO2 film enhance the charge trapping efficiency and retention property of fabricated devices. This work implies that GOQDs embedded in high-k materials are promising for charge trapping memory applications.

ReS2 based high-k dielectric stack charge-trapping and synaptic memory

The coming information era has brought about a data explosion which requires smaller and smarter memory devices. In this paper, a ReS2 based high-k dielectric stack (Al2O3/ZrO2/Al2O3) memory was fabricated as a potential candidate for future storage and computing. The device exhibits preeminent electrical characteristics, such as high On/Off current ratio (over 106 ), large memory window (4 V at a 5 V sweep voltage), fast programming and erasing speed plus excellent retention ability. Besides, our devices beautifully emulated the short/long-term potentiation/depression behavior, which shows the good synaptic properties of our device. These excellent storage and synaptic properties are promising for a wide range of applications for our memory device in the future.

Artificial Synaptic Behavior of Aloe Polysaccharides-Based Device with Au as Top Electrode

ABSTRACTFormulated, processed, and dried Aloe polysaccharides thin film sandwiched between ITO as bottom electrode and Au as top electrode has been adopted as an artificial synapse to emulate behavior of neuromorphic computing. The synaptic plasticity or weight has been modulated with this simple metal-insulator-metal structure by applying voltage sweep and voltage pulse, with excitatory postsynaptic current being monitored. Synaptic potentiation and depression has been demonstrated by applying 6 consecutive sweeps of voltage in positive and negative polarity, respectively. By varying number (10 – 50) of voltage pulses, variable synaptic weight has been measured with paired pulse facilitation and post-tetanic potentiation indexes of 2.61x10-6and 1.45x10-4, respectively. The short-term plasticity and long-term potentiation can be clearly revealed when applying 40 pulses and beyond, with extracted time constants of approximately 28 s at 40 pulses and 90 s at 50 pulses.

Improved voltage scanning method for maximum power point under partial shadow conditions

This paper proposes a novel maximum power point tracking (MPPT) algorithm with global search. The algorithm combines global voltage sweep and incremental conductance method, and introduces a Judging factor as a criterion for global voltage scanning. The Judging factor is compared with the threshold and the scan step size is selected based on the result. Take a large step when far from the peak. When approaches the peak, uses the incremental conductance method to find the local extrema and store it, then continues scanning. When the output power is close to zero, the scan is complete, Comparing all local extrema points then the global maximum power point will be found by this algorithm. Matlab simulation results show that the algorithm can find the global maximum and the search speed is fast.