Digital Memory Devices Research Articles

Mole Fraction and Device Reliability Analysis of Vertical-Tunneling-Attributed Dual-Material Double-Gate Heterojunction-TFET with Si0.7Ge0.3 Source Region at Device and Circuit Level

This paper puts forward a new vertical-tunneling-attributed dual-material double-gate heterojunction-TFET (VTDMDG-HTFET). The device structure of VTDMDG-HTFET includes Si[Formula: see text]Ge[Formula: see text] material for the designing of source region. The mechanism of vertical tunneling in VTDMDG-HTFET provides superior electric field at tunneling interface and leads to improved transfer characteristics. VTDMDG-HTFET also includes metal gate work-function engineering approach to facilitate high ON-current and small OFF-current. Application of high-[Formula: see text] dielectric material HfO2 in the form of gate oxide enhances the capacitive-coupling at channel-source interface. Moreover, the work includes the comparison of proposed VTDMDG-HTFET with the conventional vertical-tunneling based dual-material double-gate-TFET (VTDMDG-TFET). It has been observed from the simulation results that SiGe source-based VTDMDG-HTFET offers better DC characteristics in terms of superior ON-current, smaller OFF-current, steeper subthreshold-slope, lower threshold voltage, higher transconductance along with smaller drain-induced barrier-lowering (DIBL) effects as compared to its counterpart silicon-source-based VTDMDG-TFET. In this work, reliability of VTDMDG-HTFET has also been examined and compared with VTDMDG-TFET in terms of temperature sensitivity and effect of different interface trap charges. The device simulation and investigations have been carried out using technology computer aided design (TCAD) tool. Moreover, device circuit mixed-mode simulation analysis is carried out for conventional and proposed device based resistive load inverters. A comparison is performed between both the inverters in terms of prorogation delay and switching threshold voltages. Further, the mixed mode simulation analysis is also performed for the proposed device based inverter under the influence of different interface trap charges (ITCs). Study shows that reliability performance of the proposed device is better as compared to its counterpart conventional device. Hence, vertical tunneling and SiGe source-based VTDMDG-HTFET can be a better choice for various applications such as analog/RF, analog and digital electronic circuits, energy harvesting, gas-sensing and memory devices.

Defect-Stabilized Substoichiometric Polymorphs of Hafnium Oxide with Semiconducting Properties.

Hafnium oxide plays an important role as a dielectric material in various thin-film electronic devices such as transistors and resistive or ferroelectric memory. The crystallographic and electronic structure of the hafnia layer often depends critically on its composition and defect structure. Here, we report two novel defect-stabilized polymorphs of substoichiometric HfO2-x with semiconducting properties that are of particular interest for resistive switching digital or analog memory devices. The thin-film samples are synthesized by molecular beam epitaxy with oxygen engineering that allows us to cover the whole range of metallic Hf with oxygen interstitials to HfO2. The crystal and defect structures, in particular of a cubic low-temperature phase c-HfO1.7 and a hexagonal phase hcp-HfO0.7 are identified by X-ray diffraction, in vacuo electron spectroscopic, and transmission electron microscopic methods. With the help of UV/Vis transmission data, we propose a consistent band structure model for the whole oxidation range involving oxygen vacancy-induced in-gap defect states. Our comprehensive study of engineered hafnia thin films has an impact on the design of resistive memory devices and can be transferred to chemically similar suboxide systems.

MemSor: Emergence of the In‐Memory Sensing Technology for the Digital Transformation

Since Moore's law is facing several bottlenecks, electron devices are currently developing toward the trend of “More than Moore” which is based on functional diversification in terms of sensing, storage, and processing of information. This multifunctionality is thought of as another form of miniaturization of the electronic devices, where noncomputing devices are merged with digital ones, leading to faster and more energy‐efficient processing of data. Complementary to the in‐memory computing and in‐sensor computing approaches, herein, the concept of in‐memory sensing is examined in which the roles of both analog sensors and digital memory devices are integrated and achieved using a single “MemSor” device. The demonstrated optoelectronic memory devices are first reviewed, which can sense and store optical signals, and next, perspectives on the potential integration of other sensing capabilities such as pressure and gas are provided. The implementation of the in‐memory sensing technology in future energy‐efficient and scaled down electronic systems is also discussed. The challenges in the field are finally analyzed and potential solutions for the implementation of the merged sensing and storage functions using advanced manufacturing technologies are presented.

Unsupervised Clustering Method to Discriminate Dense Deception Jamming for Surveillance Radar

With the development of digital radiofrequency memory devices, the deception jamming has become a major jamming type in radar electronic counter countermeasures, especially the dense deception jamming. Recent years, some methods using signal features are proposed for specific deception jamming excision scene. It verifies the feasibility that uses signal features to discriminate deception jamming. However, discriminator training and simulation are indeed hard to achievable since no jamming samples can be obtained in advance. In this letter, we focus on the online dense deception jamming discrimination problem without the offline data training. Since deception jamming signals generated by jammers are definitely different from physical backscattering target echoes on signal features and dense jamming signals generated by one jammer has similar signal fingerprint features, an unsupervised clustering method with heuristic feature extraction is proposed. All discrimination processes are data driven and can be executed online without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> information. To evaluate its effectiveness, the proposed method is applied to a group of experimental data collected from a trial <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band radar. Results corroborate the proposed method and indicate the direction of future research.

Modeling of a tunable memory device made with a double-gate MoS2 FET and graphene floating gate

Electronic devices comprising low-temperature processed 2D materials can be utilized in back-end-of-line nonvolatile memory and logic applications, to augment conventional silicon technology. A promising structure for a low-temperature processed digital nonvolatile flash memory device and/or logic device is the double-gate MoS2 FET with a graphene floating gate and a thin h-BN gate dielectric serving as a tunneling dielectric. In this work, we show that experimental hysteretic current–voltage characteristics of this digital flash memory device can be well fit by a simple and effective physics-based model using a WKB approximation to calculate the tunneling current to the graphene floating gate and a capacitive network with 2D density-of-states to calculate the channel current flowing in the MoS2 channel. Accordingly, the model allows a device designer to predict and/or tune characteristics for this memory device, e.g., the width and center-position of the hysteresis loop as well as the value of source–drain current, as a function of both the bottom (control) gate and top (FET) gate voltages. It is noted that shifting of the center-position of the hysteresis loop enables improved reliability and functionality of the memory device in circuit applications and is a unique feature of this double-gated MoS2 FET. Overall, the demonstrated ability to well model this memory device lends further credence that 2D devices could augment silicon technology.

Digital electronics in fibres enable fabric-based machine-learning inference

Digital devices are the essential building blocks of any modern electronic system. Fibres containing digital devices could enable fabrics with digital system capabilities for applications in physiological monitoring, human-computer interfaces, and on-body machine-learning. Here, a scalable preform-to-fibre approach is used to produce tens of metres of flexible fibre containing hundreds of interspersed, digital temperature sensors and memory devices with a memory density of ~7.6 × 105 bits per metre. The entire ensemble of devices are individually addressable and independently operated through a single connection at the fibre edge, overcoming the perennial single-fibre single-device limitation and increasing system reliability. The digital fibre, when incorporated within a shirt, collects and stores body temperature data over multiple days, and enables real-time inference of wearer activity with an accuracy of 96% through a trained neural network with 1650 neuronal connections stored within the fibre. The ability to realise digital devices within a fibre strand which can not only measure and store physiological parameters, but also harbour the neural networks required to infer sensory data, presents intriguing opportunities for worn fabrics that sense, memorise, learn, and infer situational context.

The transformation of digital to analog resistance switching behavior in Bi2FeCrO6 thin films

ABSTRACT Bi2FeCrO6 (BFCO) thin films were fabricated by sol-gel method. Digital and analog resistive switching behaviors were sequentially observed in Au/BFCO/FTO/Glass structure by applying a continuous cyclic voltage. By analyzing formation mechanism of the two types of the resistive switching behaviors, it is found that the digital resistive behavior conductance mechanism is a bulk-limited conduction, and the analog resistive switching behavior is accompanied with rectification effects and negative differential resistance behaviors, which are considered as interface-limited conductivity behaviors. So the change of digital and analog resistive switching behaviors may be result of the transformation of conductive mechanism. These research results will help us to design and manufacture digital and analog multifunctional resistive switching memory devices.

Newly Found Digital Memory Characteristics of Pyrrolidone- and Succinimide-Based Polymers.

This study reports for the first time the excellent nonvolatile and volatile digital memory characteristics of polymers bearing 2-pyrrolidone and succinimide moieties. A series of new polymers is synthesized from poly(ethylene-alt-maleic anhydride) and four alcohol derivatives with and without 2-pyrrolidone and succinimide moieties. All polymers, including polyvinylpyrrolidone, are found to be thermally stable up to 195°C or higher, and characterized regarding their molecular orbital energy levels, bandgap, and resistive digital memory behaviors. Excitingly, the polymers bearing either 2-pyrrolidone or succinimide moiety demonstrate p-type digital memory behaviors with high ON/OFF current ratios and long reliabilities. Nonvolatile digital memory performance is achieved over the film thickness range of 10-80nm, whereas volatile digital memory is demonstrated over a much narrower range of film thickness. All digital memory performances can be originated from the 2-pyrrolidone and succinimide moieties possessing high affinity and stabilization power to charges via charge traps and transformations based on a hopping conduction process. Hence, these new polymers are suitable for the production of high-performance p-type nonvolatile and volatile digital memory devices. Moreover, 2-pyrrolidone and succinimide can be used as new and economical electroactive building blocks for the development of advanced digital memory materials.

Digital and analog memory devices based on 2D layered MPS3 (M = Mn, Co, Ni) materials* *Project supported by the National Key R&D Program of China (Grant Nos. 2017YFA0206200 and 2018YFB2202601) and the National Natural Science Foundation of China (Grant Nos. 61674173, 61834005, and 61902443).

We demonstrate digital and analog devices with an Ag/MPS3/Au structure based on layered MPS3 (M = Mn, Co, Ni) 2D materials. All devices show the bipolar behavior of resistive switching. In addition, Ag/MnPS3/Au and Ag/NiPS3/Au devices show synaptic characteristics of potentiation and depression. The digital and analog characteristics of resistance states enable Ag/MPS3/Au devices to work as both binary memory and artificial synapse devices. The Ag/MPS3/Au memory devices are promising for applications of flexible eye-like and brain-like systems on a chip when they are integrated with photodetectors and FETs composed of full MPS3 materials.

Simulating selective binding of a biological template to a nanoscale architecture: a core concept of a clamp-based binding-pocket-favored N-terminal-domain assembly

The biological template and its mutants have vital significance in next generation remediation, electrochemical, photovoltaic, catalytic, sensing and digital memory devices. However, a microscopic model describing the biotemplating process is generally lacking on account of modelling complexity, which has prevented widespread commercial use of biotemplates. Here, we demonstrate M13-biotemplating kinetics in atomic resolution by leveraging large-scale molecular dynamics (MD) simulations. The model reveals the assembly of gold nanoparticles on two experimentally-based M13 phage types using full M13-capsid structural models and with polarizable gold nanoparticles in explicit solvent. Both mechanistic and structural insights into the selective binding affinity of the M13 phage to gold nanoparticles are obtained based on a previously unconsidered clamp-based binding-pocket-favored N-terminal-domain assembly and also on surface-peptide flexibility. These results provide a deeper level of understanding of protein sequence-based affinity and open the route for genetically engineering a wide range of 3D electrodes for high-density low-cost device integration.

Design and Performance Improvement of CNTFET Based Content Addressable Memory (CAM) Cells

The scaling down of transistors is of paramount importance to make ICs and devices more portable and efficient. As it is the most basic component of every electronic device, there is need of finding better and innovative methods of transistor characterization. CNTFET has shown the promise and is best suited for today’s faster digital processing units and Memory devices. Here Carbon Nano Tube (CNT) is characterized for its electrical property and then designed a XOR based CAM cell using CNTFET. Both delay and power analysis for the designed CAM is done.

Digital optical memory devices based on polymer-dispersed liquid crystals films: appropriate polymer matrix morphology

ABSTRACTPermanent memory effect (PME) in polymer dispersed liquid crystal (PDLC) allows a greater applicability range than traditional PDLCs. One of the most interesting application could be the possible storing of optical information, the so-called Digital Optical Memory (DOM) devices. To test this application it would be required a display structure having an array of pixels addresses. Each pixel was filled with PDLC film with PME and electric field can be independently applied to different PDLC elements to define on/off pixel states (transparent or scattering states).PDLC films were obtained from a mixture of E7 nematic liquid crystal and poly(ethylene glycol) dimethacrylate with 875 g mol-1oligomer as precursor of the polymeric matrix. The effect of the curing temperature and the UV light intensity as well time exposure during the polymerisations on the electro-optical performance of PDLC films were investigated. In this way, a high transparency state (TOFF=55%) for a long period of time at room temperature even after the applied voltage has been switched off were obtained, started from an opaque state (T0=0%) and after reaching a transparent state (TMAX=75%), which causes 73% PME. The application to an 8x8 passive matrix using PDLC with PME is also demonstrated as proof-of-principle.

Nonequilibrium Green’s Function and First-Principles Approach to Modeling of Multiferroic Tunnel Junctions

Multiferroic tunnel junctions (MFTJs) have seen time in the spotlight lately, due to their high tunneling electroresistance and nonvolatility, which are appealing for digital memory devices. In this theoretical analysis of MFTJs, time-dependent perturbation theory yields the relation between ferroelectric polarization and ferromagnetic order at the ferroelectric/ferromagnetic interface. Furthermore, parameters for simulations are estimated from density functional theory and experimental results, and a comprehensive examination of tunneling electroresistance and tunneling magnetoresistance is conducted.

Interrupted-Sampling Repeater Jamming Suppression Based on Stacked Bidirectional Gated Recurrent Unit Network and Infinite Training

Interrupted-sampling repeater jamming (ISRJ) is coherent jamming based on digital radio frequency memory (DRFM) device, which repeatedly samples, stores, modulates, and retransmits part of the radar emitted signal, and flexibly forms false targets in the victim radar with relatively low transmitting power. It significantly interferes the radar to detect, track, and recognize targets. There are many electronic counter-countermeasures against ISRJ, among which a series of filtering methods are promising. However, it is not fully addressed. This study proposes a filtering method based on stacked bidirectional gated recurrent unit network (SBiGRU) and infinite training to fulfill the ISRJ suppression for pulse compression (PC) radar with linear frequency modulation (LFM) waveform. SBiGRU method converts signal extraction into a temporal classification problem and accurately extracts the jamming-free signal segments to generate a band pass filter to suppress the ISRJ and retain the real target signal components simultaneously. Comparing with two most advanced filtering methods in the published literature, SBiGRU method has improved the jamming-free signal extraction accuracy, leading to better performances of ISRJ suppression and real targets detection, which are verified by Monte Carlo Simulations.

Cycloidal Domains in the Magnetization Reversal Process of Ni80Fe20/Nd16Co84/Gd12Co88 Trilayers

In multilayers with weak perpendicular magnetic anisotropy, nucleation of magnetic vortex-antivortex pairs at the surfaces is set by topological characteristics, yielding a robust means to control vortex motion in extended films. However, exploiting this effect in digital memory devices would require a suitably broad range of fields supporting guided vortex motion. X-ray microscopy reveals cycloidal domains at the top surface with a stability range of tens of mT, in which propagation of magnetic vortices is effectively guided by the pattern of parallel stripes. This finding is an essential step toward the possible application of moving magnetic vortices in unpatterned films.

Large and reversible in-situ up-conversion photoluminescence modulation based on photochromism via electric-field and thermal stimulus in ferroelectrics

A large and reversible up-conversion (UC) photoluminescence modulation via both thermal and electric-field stimulus based on the photochromic reactions has been developed in a novel material: Er3+/Yb3+ co-doped K0.5Na0.5NbO3 ferroelectrics. After visible light irradiation, the ceramics exhibit a significant photochromism phenomenon turning from pale yellow to gray. The gray color can be eliminated via heat treatment or partly removed by an electric field stimulation. Upon 390-nm light irradiation for 4 min and thermal treatment at 200 °C for 5 min, the ceramics show a large modulation ratio (96%). In addition, the UC photoluminescence modulation can be in-situ operated by alternating the light irradiation and electric-field, showing an enhancing factor of 120% for the 390-nm light irradiated ceramics via applying an electric-field stimulation (12.5 kV/cm, 1 min). The developed ferroelectrics with large and reversible photoluminescence modulation through thermal stimulus and electric-field have great potential for digital memory and optoelectronic device applications.

Doped armchair germanene nanoribbon exhibiting negative differential resistance and analysing its nano-FET performance

Abstract Density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) formalism is performed to explore electronic properties (geometrical stability, band structure and density of states) and quantum transport properties (transmission spectrum and I–V characteristics) of armchair germanene nanoribbon (AGeNR) doped with various elements, such as Ga, In, Tl, As, Sb and Bi. A negative differential resistance is observed for each doped AGeNR. Our results indicate that the indium (In) atom doped AGeNR is the most geometrically stable structure and provides a maximum peak to valley current ratio (Ip/Iv = 1.95). Further, In atom doped AGeNR is proposed for field effect transistor (AGeNR-FET) formation using the high dielectric constant value of hafnium dioxide (HfO2 = 25) at different applied gate voltages (−0.5 V–0.5 V). Finally, AGeNR-FET parameters are also calculated which shows high transconductance i.e. 56,196.3 nΩ−1, high charge mobility i.e. 2.6 × 104 cm2 V−1 s−1 and low subthreshold swing i.e. 39.39 mV/decade. Our findings have great application in digital devices and memory devices, and high frequency applications for future nanoelectronics and nanodevices.

Demands for spin-based nonvolatility in emerging digital logic and memory devices for low power computing

Miniaturization of semiconductor devices is the main driving force to achieve an outstanding performance of modern integrated circuits. As the industry is focusing on the development of the 3nm technology node, it is apparent that transistor scaling shows signs of saturation. At the same time, the critically high power consumption becomes incompatible with the global demands of sustaining and accelerating the vital industrial growth, prompting an introduction of new solutions for energy efficient computations. Probably the only radically new option to reduce power consumption in novel integrated circuits is to introduce nonvolatility. The data retention without power sources eliminates the leakages and refresh cycles. As the necessity to waste time on initializing the data in temporarily unused parts of the circuit is not needed, nonvolatility also supports an instanton computing paradigm. The electron spin adds additional functionality to digital switches based on field effect transistors. SpinFETs and SpinMOSFETs are promising devices, with the nonvolatility introduced through relative magnetization orientation between the ferromagnetic source and drain. A successful demonstration of such devices requires resolving several fundamental problems including spin injection from metal ferromagnets to a semiconductor, spin propagation and relaxation, as well as spin manipulation by the gate voltage. However, increasing the spin injection efficiency to boost the magnetoresistance ratio as well as an efficient spin control represent the challenges to be resolved before these devices appear on the market. Magnetic tunnel junctions with large magnetoresistance ratio are perfectly suited as key elements of nonvolatile CMOS-compatible magnetoresistive embedded memory. Purely electrically manipulated spin-transfer torque and spin-orbit torque magnetoresistive memories are superior compared to flash and will potentially compete with DRAM and SRAM. All major foundries announced a near-future production of such memories. Two-terminal magnetic tunnel junctions possess a simple structure, long retention time, high endurance, fast operation speed, and they yield a high integration density. Combining nonvolatile elements with CMOS devices allows for efficient power gating. Shifting data processing capabilities into the nonvolatile segment paves the way for a new low power and high-performance computing paradigm based on an in-memory computing architecture, where the same nonvolatile elements are used to store and to process the information.

An Adaptive Transmitting Scheme for Interrupted Sampling Repeater Jamming Suppression.

The interrupted sampling repeater jamming (ISRJ) based on a digital radio frequency memory (DRFM) device is a new type of coherent jamming. This kind of jamming usually occurs as main-lobe jamming and has the advantages of low power requirements and easy parameter adjustment, posing a serious threat to the modern radar systems. In order to suppress the ISRJ, this paper proposes an adaptive transmitting scheme based on a phase-coded signal. The scheme firstly performs jamming perception to estimate the jamming parameters, then, on this basis, optimizes the waveform with genetic algorithm. With the optimized waveform, the jamming signal is orthogonal to the target echo, thus it can be easily suppressed with pulse compression. Simulation experiments are performed to verify the effectiveness of the scheme and the results suggest that the peak-to-side-lobe ratio (PSR) and integrated side-lobe level (ISL) of the pulse compression can be improved by about 16 dB and 15 dB, respectively, for the case where the jamming-to-signal ratio (JSR) is 13 dB.

Coupling effects of the electric field and bending on the electronic and magnetic properties of penta-graphene nanoribbons.

Quasi one-dimensional materials made from carbon have attracted a lot of attention because of their interesting properties and potential applications in electronic devices. Recently, new kinds of carbon allotropes named as penta-graphene nanoribbons (P-GNRs) have been proposed. By implementing first-principles calculations, P-GNRs exhibit large tunable band gaps under bending stress, and the band gaps of P-GNRs are easier to control than those of GNRs. In addition, the order of spin moments of P-GNRs can transform from ferromagnetic to antiferromagnetic under the coupling effect of the electric field and bending strain, thus resulting in a significant change of magnetism. Therefore, the diverse electronic and magnetic properties highlight the potential applications of P-GNRs in flexible displays, wearable computation electronics and digital memory devices.