Improvement of volatile switching in scaled silicon nanofin memristor for high performance and efficient reservoir computing.

Conductive-bridge random access memory can be used as a physical reservoir for temporal learning in reservoir computing owing to its volatile nature. Herein, a scaled Cu/HfOx/n+-Si memristor was fabricated and characterized for reservoir computing. The scaled, silicon nanofin bottom electrode formation is verified by scanning electron and transmission electron microscopy. The scaled device shows better cycle-to-cycle switching variability characteristics compared with those of large-sized cells. In addition, synaptic characteristics such as conductance changes due to pulses, paired-pulse facilitation, and excitatory postsynaptic currents are confirmed in the scaled memristor. High-pattern accuracy is demonstrated by deep neural networks applied in neuromorphic systems in conjunction with the use of the Modified National Institute of Standards and Technology database. Furthermore, a reservoir computing system is introduced with six different states attained by adjusting the amplitude of the input pulse. Finally, high-performance and efficient volatile reservoir computing in the scaled device is demonstrated by conductance control and system-level reservoir computing simulations.

Uniform multilevel switching and synaptic properties in RF-sputtered InGaZnO-based memristor treated with oxygen plasma.

Bipolar gradual resistive switching was investigated in ITO/InGaZnO/ITO resistive switching devices. Controlled intrinsic oxygen vacancy formation inside the switching layer enabled the establishment of a stable multilevel memory state, allowing for RESET voltage control and non-degradable data endurance. The ITO/InGaZnO interface governs the migration of oxygen ions and redox reactions within the switching layer. Voltage-stress-induced electron trapping and oxygen vacancy formation were observed before conductive filament electroforming. This device mimicked biological synapses, demonstrating short- and long-term potentiation and depression through electrical pulse sequences. Modulation of post-synaptic currents and pulse frequency-dependent short-term potentiation were successfully emulated in the InGaZnO-based artificial synapse. The ITO/InGaZnO/ITO memristor exhibited spike-amplitude-dependent plasticity, spike-rate-dependent plasticity, and potentiation-depression synaptic learning with low energy consumption, making it a promising candidate for large-scale integration.

Facile Synthesis of Biocarbon-Based MoS2 Composite for High-Performance Supercapacitor Application.

Nanocomposites are gaining high demand for the development of next-generation energy storage devices because of their eco-friendly and cost-effective natures. However, their short-term energy retainability and marginal stability are regarded as hindrances to overcome. In this work, we demonstrate a high-performance supercapacitor fabricated by biocarbon-based MoS2 (Bio-C/MoS2) nanoparticles synthesized by a facile hydrothermal approach using date fruits. Here, we report the high specific capacitance for a carbon-based nanocomposite employing the pyrolysis technique of converting agricultural biowaste into a highly affordable energy resource. The biocompatible Bio-C/MoS2 nanospheres exhibited a high capacitance of 945 F g-1 at a current density of 0.5 A g-1 and an excellent reproducing stability of 92% after 10000 charge/discharge cycles. In addition, the Bio-C/MoS2 NS showed an exceptional power density of 3800-8000 W kg-1 and an energy density of 74.9-157 Wh kg-1. The results would pave a new strategy for design of eco-friendly materials toward the high-performance energy storage technology.

Analytically and empirically consistent characterization of the resistive switching mechanism in a Ag conducting-bridge random-access memory device through a pseudo-liquid interpretation approach.

A new physical analysis of the filament formation in a Ag conducting-bridge random-access memory (CBRAM) device in consideration of the existence of inter-atomic attractions caused by metal bonding is suggested. The movement of Ag atoms inside the switching layer is characterized hydrodynamically using the Young-Laplace equation during set and reset operations. Both meridional and azimuthal curvatures of the Ag filament protruding from the Ag electrode are accurately calculated to track down the exact shape of the Ag filament with change in the applied voltage. The second-order partial differential equation for the Ag filament geometry is derived from the equation of equilibrium between the electrostatic pressure and the Laplace one. The solution to the equation is numerically obtained, and furthermore, the abrupt set operation in the forming process, bipolar resistive-switching, and the threshold switching operation in the reset operations are successfully simulated in accordance with the numerical solutions. Also, it is demonstrated that the currents extracted from the suggested model show good agreement with the I-V characteristics measured from the fabricated Ag CBRAM device.

Design Optimization and Analysis of InGaAs/InAs/InGaAs Heterojunction-Based Electron Hole Bilayer Tunneling FETs.

In this study, we have designed and analyzed the electron-hole bilayer (EHB) tunneling field-effect transistors (TFETs) based on various III-V compound semiconductor materials using two-dimensional (2-D) technology computer-aided design (TCAD) simulations. A recently proposed EHB TFET has lower subthreshold swing (S) and higher on-state current (Ion) than the conventional planar TFET, using band-to-band tunneling (BTBT) across the source-to-channel junction. It uses a bias-induced BTBT across the EHB formed by an electric field between the two gates. The III-V compound semiconductors have been applied to the EHB TFETs to improve the switching performances and current drivability owing to their superior material properties such as high electron mobility and high tunneling probability. After the design and analysis of devices based on various compound semiconductors, in terms of primary DC characteristics, a lower bandgap material (InAs) has been inserted in the tunneling region of the In0.53Ga0.47As EHB TFET to enhance the tunneling rate. This paper proposes an EHB TFET that uses vertically stacked InGaAs/InAs/InGaAs layers. Moreover, the design optimization process has been performed via simulations. The simulation results of the proposed EHB TFET show remarkable performances with Ion of 739.6 µA/µm, S of 1.9 mV/dec, and threshold voltage (Vth) of 7 mV at VDS 0.5 V.

Scaling Effect on Silicon Nitride Memristor with Highly Doped Si Substrate.

A feasible approach is reported to reduce the switching current and increase the nonlinearity in a complementary metal-oxide-semiconductor (CMOS)-compatible Ti/SiNx /p+ -Si memristor by simply reducing the cell size down to sub-100 nm. Even though the switching voltages gradually increase with decreasing device size, the reset current is reduced because of the reduced current overshoot effect. The scaled devices (sub-100 nm) exhibit gradual reset switching driven by the electric field, whereas that of the large devices (≥1 µm) is driven by Joule heating. For the scaled cell (60 nm), the current levels are tunable by adjusting the reset stop voltage for multilevel cells. It is revealed that the nonlinearity in the low-resistance state is attributed to Fowler-Nordheim tunneling dominating in the high-voltage regime (≥1 V) for the scaled cells. The experimental findings demonstrate that the scaled metal-nitride-silicon memristor device paves the way to realize CMOS-compatible high-density crosspoint array applications.

Simulation of One-Transistor Dynamic Random-Access Memory Based on Symmetric Double-Gate Si Junctionless Transistor.

In this study, one-transistor dynamic random-access memory (1T-DRAM) based on a symmetric double-gate Si junctionless transistor is proposed using technology computer-aided design simulation. The proposed device uses double gates that play different roles in realizing 1T-DRAM operation. Gate 1 is used as a switching node, and Gate 2 is used as a storage node. By controlling the different two gate workfunctions, a potential barrier is adjusted to store hole effectively. The operation characteristics were investigated regarding four different memory operation states to write "1", write "0", read, and hold. Also, the effects of two different gate workfunctions on sensing margin and retention characteristics are closely investigated. Through a set of optimally set gate workfunctions, 33 µA/µm of sensing margin and 38 ms of retention time have been obtained.

InGaN/GaN light-emitting diode having direct hole injection plugs and its high-current operation.

The light-emitting diode (LED) with an improved hole injection and straightforward process integration is proposed. p-type GaN direct hole injection plugs (DHIPs) are formed on locally etched multiple-quantum wells (MQWs) by epitaxial lateral overgrowth (ELO) method. We confirm that the optical output power is increased up to 23.2% at an operating current density of 100 A/cm2. Furthermore, in order to identify the origin of improvement in optical performance, the transient light decay time and light intensity distribution characteristics were analyzed on the DHIP LED devices. Through the calculation of the electroluminescence (EL) decay time, internal quantum efficiency (IQE) is extracted along with the recombination parameters, which reveals that the DHIPs have a significant effect on enhancement of radiative recombination and reduction of efficiency droop. Furthermore, the mapping PL reveals that the DHIP LED also has a potential to improve the light extraction efficiency by hexagonal pyramid shaped DHIPs.

Nano-cone resistive memory for ultralow power operation.

SiN x -based nano-structure resistive memory is fabricated by fully silicon CMOS compatible process integration including particularly designed anisotropic etching for the construction of a nano-cone silicon bottom electrode (BE). Bipolar resistive switching characteristics have significantly reduced switching current and voltage and are demonstrated in a nano-cone BE structure, as compared with those in a flat BE one. We have verified by systematic device simulations that the main cause of reduction in the performance parameters is the high electric field being more effectively concentrated at the tip of the cone-shaped BE. The greatly improved nonlinearity of the nano-cone resistive memory cell will be beneficial in the ultra-high-density crossbar array.

FeNP@MIL-101(Fe)-Based Carbon Nanotube Composite for Energy Storage Applications.

Metal-organic frameworks (MOFs) are of great interest for energy applications due to their high porosity, high charge storage capacity, and large number of active redox sites. It is important to enhance the performance of metal-organic frameworks through modification in order to increase their potential applications. Unique Fe nanoparticle (NP) in the Materials of Institute Lavoisier (MIL) series embedded in the carbon nanotube (CNT), FeNP@MIL-101(Fe)/CNT-based, nanocomposites have been synthesized using suitable hierarchical micromesoporous structures. These were fabricated by simple and straightforward solvothermal methods, and their electrochemical charge storage performance was investigated. The energy storage application using the FeNP@MIL -101(Fe)/CNT composite as a supercapacitor electrode was implemented for the first time. Various techniques were used to characterize this composite. It has excellent electrochemical properties when used as electrode material in 1 M KOH solution, including a high capacitance of up to 1305 F g-1 at 1 A g-1 and a long cycling stability of 95.7% capacitance retention after 10,000 cycles. Moreover, symmetric two-electrode electrochemical experiments showed that the composite achieved an energy density of 98.65 Wh kg-1 and a power density of 9000 W kg-1, The combination of microporous and mesoporous structures, increased surface area, and higher electrical conductivity are the main reasons for the high performance. The integration of FeNP@MIL-101(Fe) with the CNT creates new ion diffusion pathways, improves the hierarchical pore properties, and exposes the FeNP@MIL-101(Fe) cluster to more redox active sites, which improves the charge storage performance.

Analysis on RF parameters of nanoscale tunneling field-effect transistor based on InAs/InGaAs/InP heterojunctions.

Tunneling field-effect transistors (TFETs) based on the quantum mechanical band-to-band tunneling (BTBT) have advantages such as low off-current and subthreshold swing (S) below 60 mV/dec at room temperature. For these reasons, TFETs are considered as promising devices for low standby power (LSTP) applications. On the other hand, silicon (Si)-based TFETs have a drawback in low on-state current (lon) drivability. In this work, we suggest a gate-all-around (GAA) TFET based on compound semiconductors to improve device performances. The proposed device materials consist of InAs (source), InGaAs (channel), and InP (drain). According to the composition (x) of Ga in In1-xGa(x)As layer of the channel region, simulated devices have been investigated in terms of both direct-current (DC) and RF parameters including tunneling rate, transconductance (g(m)), gate capacitance (Cg), intrinsic delay time (tau), cut-off frequency (fT) and maximum oscillation frequency (f(max)). In this study, the obtained maximum values of tau, fT, and f(max) for GAA InAs/In0.9Ga0.1As/InP heterojunction TFET were 21.2 fs, 7 THz, and 18 THz, respectively.

Short-Term Memory Characteristics of IGZO-Based Three-Terminal Devices.

A three-terminal synaptic transistor enables more accurate controllability over the conductance compared with traditional two-terminal synaptic devices for the synaptic devices in hardware-oriented neuromorphic systems. In this work, we fabricated IGZO-based three-terminal devices comprising HfAlOx and CeOx layers to demonstrate the synaptic operations. The chemical compositions and thicknesses of the devices were verified by transmission electron microscopy and energy dispersive spectroscopy in cooperation. The excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), short-term potentiation (STP), and short-term depression (STD) of the synaptic devices were realized for the short-term memory behaviors. The IGZO-based three-terminal synaptic transistor could thus be controlled appropriately by the amplitude, width, and interval time of the pulses for implementing the neuromorphic systems.

The Enhanced Performance of Neuromorphic Computing Hardware in an ITO/ZnO/HfOx/W Bilayer-Structured Memory Device.

This study discusses the potential application of ITO/ZnO/HfOx/W bilayer-structured memory devices in neuromorphic systems. These devices exhibit uniform resistive switching characteristics and demonstrate favorable endurance (>102) and stable retention (>104 s). Notably, the formation and rupture of filaments at the interface of ZnO and HfOx contribute to a higher ON/OFF ratio and improve cycle uniformity compared to RRAM devices without the HfOx layer. Additionally, the linearity of potentiation and depression responses validates their applicability in neural network pattern recognition, and spike-timing-dependent plasticity (STDP) behavior is observed. These findings collectively suggest that the ITO/ZnO/HfOx/W structure holds the potential to be a viable memory component for integration into neuromorphic systems.

Analog Memory and Synaptic Plasticity in an InGaZnO-Based Memristor by Modifying Intrinsic Oxygen Vacancies.

This study focuses on InGaZnO-based synaptic devices fabricated using reactive radiofrequency sputtering deposition with highly uniform and reliable multilevel memory states. Electron trapping and trap generation behaviors were examined based on current compliance adjustments and constant voltage stressing on the ITO/InGaZnO/ITO memristor. Using O2 + N2 plasma treatment resulted in stable and consistent cycle-to-cycle memory switching with an average memory window of ~95.3. Multilevel resistance states ranging from 0.68 to 140.7 kΩ were achieved by controlling the VRESET within the range of -1.4 to -1.8 V. The modulation of synaptic weight for short-term plasticity was simulated by applying voltage pulses with increasing amplitudes after the formation of a weak conductive filament. To emulate several synaptic behaviors in InGaZnO-based memristors, variations in the pulse interval were used for paired-pulse facilitation and pulse frequency-dependent spike rate-dependent plasticity. Long-term potentiation and depression are also observed after strong conductive filaments form at higher current compliance in the switching layer. Hence, the ITO/InGaZnO/ITO memristor holds promise for high-performance synaptic device applications.

Correction: Synaptic plasticity and non-volatile memory characteristics in TiN-nanocrystal-embedded 3D vertical memristor-based synapses for neuromorphic systems.

Correction for 'Synaptic plasticity and non-volatile memory characteristics in TiN-nanocrystal-embedded 3D vertical memristor-based synapses for neuromorphic systems' by Seyeong Yang et al., Nanoscale, 2023, https://doi.org/10.1039/D3NR01930F.

Synaptic plasticity and non-volatile memory characteristics in TiN-nanocrystal-embedded 3D vertical memristor-based synapses for neuromorphic systems.

Although vertical configurations for high-density storage require challenging process steps, such as etching high aspect ratios and atomic layer deposition (ALD), they are more affordable with a relatively simple lithography process and have been employed in many studies. Herein, the potential of memristors with CMOS-compatible 3D vertical stacked structures of Pt/Ti/HfOx/TiN-NCs/HfOx/TiN is examined for use in neuromorphic systems. The electrical characteristics (including I-V properties, retention, and endurance) were investigated for both planar single cells and vertical resistive random-access memory (VRRAM) cells at each layer, demonstrating their outstanding non-volatile memory capabilities. In addition, various synaptic functions (including potentiation and depression) under different pulse schemes, excitatory postsynaptic current (EPSC), and spike-timing-dependent plasticity (STDP) were investigated. In pattern recognition simulations, an improved recognition rate was achieved by the linearly changing conductance, which was enhanced by the incremental pulse scheme. The achieved results demonstrated the feasibility of employing VRRAM with TiN nanocrystals in neuromorphic systems that resemble the human brain.

Room-temperature electroluminescence from germanium in an Al(0.3)Ga(0.7)As/Ge heterojunction light-emitting diode by Γ-valley transport.

Group-IV materials for monolithic integration with silicon optoelectronic systems are being extensively studied. As a part of efforts, light emission from germanium has been pursued with the objective of evolving germanium into an efficient light source for optical communication systems. In this study, we demonstrate room-temperature electroluminescence from germanium in an Al(0.3)Ga(0.7)As/Ge heterojunction light-emitting diode without any complicated manipulation for alternating material properties of germanium. Electroluminescence peaks were observed near 1550 nm and the energy around this wavelength corresponds to that emitted from direct recombination at the Γ-valley of germanium.

Novel Au nanorod/Cu2O composite nanoparticles for a high-performance supercapacitor.

Metal-oxide nanomaterials have attracted great interest in recent years due to their novel characteristics such as surface effect and quantum confinement. A fascinating Au nanorod (NR)/cuprous oxide core-shell composite (AuNR/Cu2O) was directly synthesized using a moderate one-pot facile green redox method and further utilized for energy storage applications in a supercapacitor. The synthesis mechanism is based on the use of reducing agents to form the core shell. The resultant composite was deposited on the surface of nickel foam as a result of redox reactions between Au and Cu via a hydrothermal method. AuNR/Cu2O composite nanoparticles (NPs) were characterized using various spectroscopic and microscopic techniques, including UV-vis and X-ray photoelectron spectroscopies, Brunauer-Emmett-Teller surface area analysis, X-ray diffractometry, and transmission electron microscopy. The AuNR/Cu2O composite NPs grow via the depositing of a 20-50 nm Cu2O shell on an AuNR core with dimensions of 5-20 nm in width and 40-70 nm in length. The as-synthesized AuNR/Cu2O composite NPs were effectively used as electrode materials in a supercapacitor, and their electrochemical performance was determined by cyclic voltammetry, galvanostatic charge-discharge measurements, and electrochemical impedance spectroscopy in 2 M KOH aqueous solution as an electrolyte. The composite NPs showed excellent average specific capacitance of 235 F g-1 at a current density of 2 A g-1 and durable cycling stability (96% even after 10 000 cycles). The higher efficiency of the AuNR/Cu2O composite NPs can be attributed to the presence of AuNR in the core. The AuNR/Cu2O composite NPs exhibit a high surface area and high electrical conductivity, which consequently result in their excellent specific capacitance and outstanding rate as an all-solid-state supercapacitor electrode.

Medium-Temperature-Oxidized GeOx Resistive-Switching Random-Access Memory and Its Applicability in Processing-in-Memory Computing.

Processing-in-memory (PIM) is emerging as a new computing paradigm to replace the existing von Neumann computer architecture for data-intensive processing. For the higher end-user mobility, low-power operation capability is more increasingly required and components need to be renovated to make a way out of the conventional software-driven artificial intelligence. In this work, we investigate the hardware performances of PIM architecture that can be presumably constructed by resistive-switching random-access memory (ReRAM) synapse fabricated with a relatively larger thermal budget in the full Si processing compatibility. By introducing a medium-temperature oxidation in which the sputtered Ge atoms are oxidized at a relatively higher temperature compared with the ReRAM devices fabricated by physical vapor deposition at room temperature, higher device reliability has been acquired. Based on the empirically obtained device parameters, a PIM architecture has been conceived and a system-level evaluations have been performed in this work. Considerations include the cycle-to-cycle variation in the GeOx ReRAM synapse, analog-to-digital converter resolution, synaptic array size, and interconnect latency for the system-level evaluation with the Canadian Institute for Advance Research-10 dataset. A fully Si processing-compatible and robust ReRAM synapse and its applicability for PIM are demonstrated.

Optimization of Feedback FET with Asymmetric Source Drain Doping Profile.

A feedback field-effect transistor (FBFET) is a novel device that uses a positive feedback mechanism. FBFET has a high on-/off ratio and is expected to realize ideal switching characteristics through steep changes from off-state to on-state. In this paper, we propose and optimize FBFET devices with asymmetric source/drain doping concentrations. Additionally, we discuss the changes in electrical characteristics across various channel length and channel thickness conditions and compare them with those of FBFET with a symmetric source/drain. This shows that FBFET with an asymmetric source/drain has a higher on-/off ratio than FBFET with a symmetric source/drain.