Low Current Operation Research Articles

Organic synaptic transistor showing ultralow energy consumption with a microscale channel by laser ablation

Low energy consumption per synaptic event is important for artificial synapses in applications of highly integrated and large-scale neuromorphic computing systems. Reducing the channel length of a synaptic transistor is an effective method to achieve this goal because such devices can work under low operating voltage and current. In this Letter, we use femtosecond laser ablation to fabricate a microscale slit in an Ag film as the channel of an organic synaptic transistor to obtain low energy consumption. The length of the shortest channel is only 1.6 μm. As a result, the device could be driven by a 50 μV drain bias voltage while output 855 pA excitatory postsynaptic current under a gate spike of 50 mV and 30 ms. The calculated energy consumption per synaptic event is 1.28 fJ, which is comparable to that of a biological synapse (1–10 fJ per synaptic event). Femtosecond laser ablation has been demonstrated a rapid and effective process for the fabrication of microscale channel with high resolution for synaptic transistor, showing large potential for the development of neuromorphic electronics.

Applicability of linear models in modeling dynamic behavior of alkaline water electrolyzer stack

Linear equivalent circuit models are commonly used to estimate the effect of current ripple on the performance of water electrolyzers, thus it is important that the validity of this approach is examined. The effect of the amplitude and frequency of the sinusoidal current ripple on the performance of the alkaline water electrolyzer stack is studied experimentally. The increased current ripple amplitude produces additional losses in the electrolyzer stack, while the effect of ripple frequency appears to be insignificant. Linear models based on an equivalent circuit and polarization curve tangent are compared with waveform measurements with differing ripple amplitudes and frequencies to study their dynamic modeling capabilities. Under dynamic operation the experimental results show that operating voltage differs considerably from the static polarization curve, especially at low operating currents, due to nonlinear behavior. It is also shown that the dynamic equivalent circuit model using only linear components is not enough to accurately model electrolyzer behavior under dynamic operation.

Direct electron transfer mediated electrochemical activation of persulfates by reticulated vitreous carbon (RVC) cathode

The electrochemical activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) for pollutant degradation has gained increasing attention. In this work, reticulated vitreous carbon (RVC) electrodes were prepared at a low cost and investigated for the cathodic activation of PMS/PDS for Acid Orange 7 degradation. The RVC was characterized by SEM, TGA, XRD, Raman spectroscopy, XPS, EIS, and compression test. The superior activity outperformed previous reports in terms of low current density operation (1–10 mA/cm2), high degradation rates (0.13–0.49 min−1), low energy consumption (0.03–0.23 kWh/m3/order) without involvement of catalysts. The process was optimized for current density, PMS dosage, pollutant concentration, pH, water matrix, and supporting electrolyte. Under the optimal current density (3 mA/cm2), the addition of 0.5 mM of PMS boosted the degradation rate by 9.6 times to 0.4470 min−1 and reduced the electrical energy consumption by 90.1 % to 0.0243 kWh/m3/order in 50 mM of Na2SO4. Moreover, up to 117 mg/L of H2O2 was produced in 1 hour by the reduction of oxygen, with current efficiencies between 78–24 %. The process showed little deterioration in 10 cycles, worked for a variety of pollutants, and was not affected by the water matrix. The H-cell experiments confirmed that 90 % degradation took place on the cathode. Scavenging experiments and electrochemical tests suggested that the transitional state of PMS* and O2•− mediated the direct electron transfer mechanism for AO7 degradation. Eighteen degradation products were identified by HPLC-MS and categorized into 4 degradation pathways. Finally, their toxicity was assessed by the ECOSAR programme.

Switching layer optimization in Co-based CBRAM for >105 memory window in sub-100 µA regime

Co/HfO2-based CBRAM stacks are optimized to enlarge the memory window for low-current (50 µA) operation. First, we dope the switching layer with Si to decrease the pristine current, thus enlarging the memory window. Then, we reduce the forming voltage by scaling the Si-doped HfO2 thickness. Finally, we extend the endurance lifetime and reduce the write time by introducing a hygroscopic oxide, LaSiO, in combination with HfSiO, to enhance Co ion hopping through hydroxyl groups. We further outline the important role of the position of the hygroscopic layer with respect to the Co active electrode in enlarging the memory window of the CBRAM device up to > 105.

P‐142: Confocal Photoluminescence and Electroluminescence of Blue InGaN/GaN Nanorod Light‐emitting Diodes with Different Passivation Approaches

The sidewall passivation is essential to achieve high micro light‐emitting diode (LED) efficiency. We investigated different sidewall passivation strategies on InGaN/GaN blue nLED, including Thermal ALD and PEALD Al2O3. The characterization of temperature and laser excitation‐dependent photoluminescence (PL) and time‐resolved photoluminescence (TRPL) were observed to determine the efficiency. Sidewall passivated‐nLED device was fabricated and characterized. The device exhibits extremely high brightness, even at low operation current.

Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation

In this work, the optical efficiency of III-nitride blue micro-LEDs (μLEDs) ranged from 5 × 5 to 60 × 60 μm2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passivation using atomic layer deposition (ALD) has superior optical enhancement compared to conventional RF sputtering, where most of the enhancement occurred at low current density range. Additionally, the use of ALD sidewall passivation and chemical treatment offered significant efficiency improvement for different sizes of μLEDs at operating less than 1 A cm−2 and the devices without sidewall treatments did not emit light. The effect of sidewall treatments to the effective Shockley–Read–Hall (SRH) nonradiative recombination coefficient, or the effective A coefficient from the ABC model, was estimated. The effective SRH nonradiative recombination coefficient was suppressed by two orders of magnitude for devices with sidewall treatments compared to devices without sidewall passivation.

Novel integration of thermoelectric distiller with direct contact membrane distillation

A thermoelectric distiller (TED) integrated with a direct contact membrane distillation (DCMD) unit was proposed and numerically investigated. The mathematical models of the hybrid TED--–DCMD system were developed and validated. In the proposed hybrid system, the TED provides the heating demand of the DCMD desalination unit in four novel configurations of TED-DCMD integration. The first configuration integrates the TED-DCMD by adding a DCMD heat exchanger coil inside the condensation tank of a TED, while the second configuration involves two TED condensation tanks with each tank containing a DCMD heat exchanger coil. The third configuration also consists of two TED tanks with an external heat exchanger where thermal energy from the TED produced water is transferred to the DCMD feed stream. The fourth configuration is a modification of the second configuration with a thermal recovery from TED produced water for inlet feed water preheating. To investigate the performance (distillate productivity, specific energy consumption, coefficient of performance, and ratio of TED productivity) of each integrated TED-DCMD configuration, the effects of different operating parameters such as DCMD feed flow rate, TEM current, number of TEMs, and TED produced water temperature were examined. Findings indicated that the third configuration is the most energy efficient, with specific energy consumption (SEC) reaching a minimum value of 217 kWh/m3 at low current operation of 2.1 A, and feed flow rate of 4.0 L/min for 8.0 TEMs in the TED. A maximum freshwater productivity and COPh of 2.74 kg/s and 3.24, are attained by the 4th and 3rd configurations, respectively. Results also indicated that elevating the current input encourages higher water productivity. Meanwhile, higher values of SEC and water productivity are attained when operating TED at saturation temperature.

Nanoporous Nickel Cathode with an Electrostatic Chlorine-Resistant Surface for Industrial Seawater Electrolysis Hydrogen Production.

Seawater electrolysis presents a promising avenue for green hydrogen production toward a carbon-free society. However, the electrode materials face significant challenges including severe chlorine-induced corrosion and high reaction overpotential, resulting in low energy conversion efficiency and low current density operation. Herein, we put forward a nanoporous nickel (npNi) cathode with high chlorine corrosion resistance for energy-efficient seawater electrolysis at industrial current densities (0.4-1 A cm-2). With the merits of an electrostatic chlorine-resistant surface, modulated Ni active sites, and a robust three-dimensional open structure, the npNi electrode showed a low hydrogen evolution reaction overpotential of 310 mV and a high electricity-hydrogen conversion efficiency of 59.7% at 400 mA cm-2 in real seawater and outperformed most Ni-based seawater electrolysis cathodes in recent publications and the commercial Ni foam electrode (459 mV, 46.4%) under the same test condition. In situ electrochemical impedance spectroscopy, high-frame-rate optical microscopy, and first-principles calculation revealed that the improved corrosion resistance, enhanced intrinsic activity, and mass transfer were responsible for the lowered electrocatalytic overpotential and enhanced energy efficiency.

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

AbstractPorous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra‐low thicknesses of ≈20 µm which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir‐loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X‐ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state‐of‐the‐art commercially available PTL materials by up to 100 mV at 7 A cm−2 in combination with low‐loaded catalyst‐coated membranes of 0.4 mgIr cm−2. Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost‐effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in‐plane resistance of low‐loaded catalyst layers.

Experimental demonstration of combination-encoding content-addressable memory of 0.75 bits per switch utilizing Hf-Zr-O ferroelectric tunnel junctions.

We experimentally demonstrate the concept of combination-encoding content-addressable memory (CECAM) that offers much higher content density than any other content-addressable memory devices proposed to date. In this work, CECAM was fabricated and validated with a hafnium-zirconium oxide (HZO) ferroelectric tunnel junction (FTJ) crossbar array. The new CAM structure, which utilizes nonvolatile memory devices, offers numerous advantages including low-current operation (FTJ), standby power reduction (ferroelectric HZO), and increased content density. Multibit data are encoded and stored in multi-switch CECAM. Perfect-match searching in CECAM with a reasonable match current (lower than nA) for different sizes of CECAM has been validated from a novel CAM device. We demonstrate N-CECAM (with keys encoded into 2N-long binary arrays) for N = 3 (using 6 FTJs) and 4 (using 8 FTJs), leading to content densities of 0.667 and 0.75 bits per switch, which highlight 33% and 50% increase in content density compared to that of the conventional TCAM (0.5 bits per switch).

Resistive switching and battery-like characteristics in highly transparent Ta2O5/ITO thin-films

Highly transparent resistive-switching (RS) devices were fabricated by growing amorphous tantalum pentoxide (a-Ta2O5) and indium tin oxide (a-ITO) thin films on barium-borosilicate glass (7059) substrates, using electron beam evaporation. These layers exhibited the transmittance greater than ~ 85% in the full visible region and showed RS behavior and battery-like IV characteristics. The overall characteristics of RS can be tuned using the top electrode and the thickness of a-Ta2O5. Thinner films showed a conventional RS behavior, while thicker films with metal electrodes showed a battery-like characteristic, which could be explained by additional redox reactions and non-Faradaic capacitive effects. Devices having battery-like IV characteristics showed higher enhanced, retention and low-operation current.

Micro-Transfer-Printed Membrane Distributed Reflector Lasers on Si Waveguide Modulated With 50-Gbit/s NRZ Signal

In this work, we fabricate directly modulated membrane distributed reflector (DR) lasers on a Si waveguide by utilizing micro-transfer printing method. Micro-transfer printing enables low-loss coupling between the lasers and the silicon photonics circuit, and since it is a back-end process, we can test the lasers prior to integration. A membrane laser is as thick as the Si waveguides, which makes optical coupling between the two quite easy. In addition, membrane lasers with a lateral <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> diode structure have low capacitance and a large optical confinement factor, which means they can achieve a low threshold current and high-speed modulation operation with low energy consumption. The fabricated membrane DR laser integrated with a 220-nm-thick Si waveguide exhibits a low threshold current of 1.2 mA and single-mode operation at 1535 nm with a side-mode suppression ratio (SMSR) of about 40 dB at the bias current of 14 mA. It also achieves the E-O bandwidth of over 25 GHz and 50-Gbit/s non-return-to-zero (NRZ) signal modulation with an extinction ratio of 2.5 dB.

Low Dark Current Operation in InAs/GaAs(111)A Infrared Photodetectors: Role of Misfit Dislocations at the Interface.

We demonstrate an extended short-wave infrared (e-SWIR) photodetector composed of an InAs/GaAs(111)A heterostructure with interface misfit dislocations. The layer structure of the photodetector consists simply of an n-InAs optical absorption layer directly grown with a thin undoped-GaAs spacer layer on n-GaAs by molecular beam epitaxy. The lattice mismatch was abruptly relaxed by forming a misfit dislocation network at the initial stage of the InAs growth. We found high-density threading dislocations (1.5 × 109 cm-2) in the InAs layer. The current-voltage characteristics of the photodetector at 77 K had a very low dark current density (<1 × 10-9 A cm-2) at a positive applied voltage (electrons flow from n-GaAs to n-InAs) of up to ∼+1 V. Simulation of the band structure revealed that the direct connection of GaAs and InAs and the formation of interfacial states by the misfit dislocations play significant positive roles in suppressing dark current. Under illumination with e-SWIR light at 77 K, a clear photocurrent signal was observed with a 2.6 μm cutoff wavelength, which is consistent with the bandgap of InAs. We also demonstrated e-SWIR detection at room temperature with a 3.2 μm cutoff wavelength. The maximum detectivity at 294 K exceeds 2 × 108 cm Hz0.5 W-1 for the detection of e-SWIR light at 2 μm.

Internal ion transport in ionic 2D CuInP2S6 enabling multi-state neuromorphic computing with low operation current

Memristor-based neuromorphic computing is promising for artificial intelligence. However, most of the reported memristors have limited linear computing states and consume large operation energy which hinder their applications. Herein, we report a memristor based on ionic two-dimensional CuInP2S6 (2D CIPS), in which up to 1350 linear conductance states are achieved by controlling the migration of internal Cu ions in CIPS. In addition, the device shows a low operation current of ∼100 pA. Cu ions are proven to move along the electric field by in-situ scanning electron microscopy and energy dispersive spectroscopy measurements. Furthermore, complex signal transport among multiple neurons in the brain is imitated by 2D CIPS-based memristor arrays. Our results offer a new platform to fabricate high-performance memristors based on ion transport in 2D materials for neuromorphic computing.

NbO2 selector device with Ge2Sb2Te5 thermal barrier for low off current (300 nA) and low power operation

This study investigated the impact of a Ge2Sb2Te5 (GST) thermal barrier on the performance of NbO2-based selector devices. Our findings showed that the GST barrier could significantly decrease the off-state leakage current from 3 μA to 300 nA without increasing the threshold switching voltage owing to its insulation properties and high thermal resistance. We also found that the GST barrier can effectively contain the Joule heat within the NbO2 switching region, as confirmed through a cryogenic analysis of the thermal resistance of GST. The results showed that the GST/NbO2 device had a thermal resistance 3.48 times higher than that of a single-layer NbO2 device. Our results provide design guidelines for utilizing a barrier layer to reduce the leakage current in low-power threshold switching devices.

Design and synthesis of a solution-processed redox-active bis(formazanate) zinc complex for resistive switching applications.

In this paper, we report the synthesis and characterization of a mononuclear zinc complex (1) containing a redox-active bis(4-antipyrinyl) derivative of the 3-cyanoformazanate ligand. Complex 1 was readily obtained by refluxing zinc acetate with 3-cyano-1,5-(4-antipyrinyl)formazan (LH) in a methanolic solution. Single-crystal X-ray diffraction analysis of complex 1 shows that the formazanate ligands bind to the zinc center in a five-member chelate "open" form via the 1- and 4-positions of the 1,2,4,5-tetraazapentadienyl formazanate backbone leading to the formation of the mononuclear bis(formazanate) zinc complex exhibiting a distorted octahedral geometry. We also report the study of resistive-switching random access memory application of this solution-processable bis(formazanate) Zn(II) complex to facilitate the practical implementation of transition metal complex-based molecular memory devices. The complex demonstrated high conductance switching with a large ON-OFF ratio, good stability, and a long retention time. A trap-controlled space charge limited current mechanism is proposed for the observed resistive switching behavior of the device, wherein the role played by the [ZnIIL2] complex that comprises the extended redox-active conjugated ligand backbone is revealed by corroborating electrochemical studies, spectrochemical experiments, and DFT calculations. In addition to providing significant insights into the molecular design of transition metal complexes for memory applications, this study also presents the utilization of ZnIIL2 towards the realization of non-volatile resistive random access memory (RRAM) devices with inorganic/organic hybrid active layers that are highly cost-effective and sustainable. These devices exhibited multilevel switching and low current operation, both of which are desirable for advanced memory applications.

Variability-Controlled HfZrO2 Ferroelectric Tunnel Junctions for Reservoir Computing

We propose reservoir computing (RC), a framework for constructing recurrent neural networks (RNNs) with simple training rule, using ferroelectric tunnel junction (FTJ) crossbar array. Not only the weights of connection between reservoir layer and output layer need to be trained, but also random fixed weights within reservoir layer can be realized by the conductance of FTJs. Random weights within reservoir layers have optimal variability, which is dependent not on the type of the distribution but on the reservoir size. Optimal variability can be attained by device-to-device variability in FTJs together with analog converters on the wordlines and the bitlines. Analog resistive switching characteristics in FTJs can also realize the weights connected to output layer, which need to be trained. Furthermore, device-to-device variability in Hf <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{1}- {x}}$ </tex-math></inline-formula> ZrxO2 (HZO) FTJ is extensively investigated. Taking into account the low current operation in FTJs, RC with FTJ crossbar array is a potential candidate for neuromorphic computing system with low power consumption.

Ultrathin HfO2/Al2O3 bilayer based reliable 1T1R RRAM electronic synapses with low power consumption for neuromorphic computing

Neuromorphic computing requires highly reliable and low power consumption electronic synapses. Complementary-metal-oxide-semiconductor (CMOS) compatible HfO2 based memristors are a strong candidate despite of challenges like non-optimized material engineering and device structures. We report here CMOS integrated 1-transistor-1-resistor (1T1R) electronic synapses with ultrathin HfO2/Al2O3 bilayer stacks (<5.5 nm) with high-performances. The layer thicknesses were optimized using statistically extensive electrical studies and the optimized HfO2(3 nm)/ Al2O3(1.5 nm) sample shows the high reliability of 600 DC cycles, the low Set voltage of ∼0.15 V and the low operation current of ∼6 µA. Electron transport mechanisms under cycling operation of single-layer HfO2 and bilayer HfO2/Al2O3 samples were compared, and it turned out that the inserted thin Al2O3 layer results in stable ionic conduction. Compared to the single layer HfO2 stack with almost the same thickness, the superiorities of HfO2/Al2O3 1T1R resistive random access memory (RRAM) devices in electronic synapse were thoroughly clarified, such as better DC analog switching and continuous conductance distribution in a larger regulated range (0–700 µS). Using the proposed bilayer HfO2/Al2O3 devices, a recognition accuracy of 95.6% of MNIST dataset was achieved. These results highlight the promising role of the ultrathin HfO2/Al2O3 bilayer RRAM devices in the application of high-performance neuromorphic computing.

Reservoir Computing with Charge-Trap Memory Based on a MoS2 Channel for Neuromorphic Engineering.

Novel memory devices are essential for developing low power, fast, and accurate in-memory computing and neuromorphic engineering concepts that can compete with the conventional complementary metal-oxide-semiconductor (CMOS) digital processors. 2D semiconductors provide a novel platform for advanced semiconductors with atomic thickness, low-current operation, and capability of 3D integration. This work presents a charge-trap memory (CTM) device with a MoS2 channel where memory operation arises, thanks to electron trapping/detrapping at interface states. Transistor operation, memory characteristics, and synaptic potentiation/depression for neuromorphic applications are demonstrated. The CTM device shows outstanding linearity of the potentiation by applied drain pulses of equal amplitude. Finally, pattern recognition is demonstrated by reservoir computing where the input pattern is applied as a stimulation of the MoS2 -based CTMs, while the output current after stimulation is processed by a feedforward readout network. The good accuracy, the low current operation, and the robustness to input random bit flip makes the CTM device a promising technology for future high-density neuromorphic computing concepts.

Interleaved High Gain DC/DC Boost Converter-Based Proton Exchange Membrane Fuel Cell Fault-Tolerant Control

Despite the development witnessed by fuel cell systems and considering them as a promising technology in the future. Faults management in Proton Exchange Membrane Fuel Cell systems remains the major obstacle to meeting durability and reliability requirements for their use and commercialization, especially in automotive applications. DC/DC converters are used for power conditioning purposes in fuel cell systems, and can be also used in fault management. This study presents a promising solution for managing the most common faults in fuel cell systems (flooding and drying phenomena). The Fault-tolerant control is applied to an Interleaved High Gain DC/DC Boost Converter (IHGBC) associated with the fuel cell in event of faults. The strategy applied to the DC/DC converter controls the fuel cell current and voltage operating points, mitigating the fuel cell fault. The current drawn by the fuel cell changes according to the fault occurrence. a low current density operation offers the possibility of mitigating the flood fault, while the high current density process has advantage of increasing the water production in the cathode and thus avoiding the membrane drying. The simulation and experimental results demonstrated the effectiveness of the proposed fault-tolerant control strategy in improving cell performance and restoring the optimal operation.