Switching Memory Research Articles

Abstract 525: Uncovering Mechanisms Between Oligosaccharide Galactose-alpha 1,3-galactose (alpha-gal) Sensitization And Atherosclerosis

Recent work by our group and others have shown individuals with IgE to the oligosaccharide allergen present in mammalian products (α-gal) have increased atheroma burden with increased necrosis and calcification compared to those without α -gal specific IgE. These data suggest α -gal specific IgE increase plaque severity and vulnerability, yet the mechanisms that promote production of IgE to α -gal are unknown. Previous work from our group utilized multi-omics single cell analysis of circulating PBMCs from subjects with coronary angiography at UVA and showed subjects with IgE α -gal sensitization had a higher frequency of CCR6hi switched memory (SWM) B cells and that the CCR6 ligand, CCL20, increased class switching to IgE. To determine mechanisms whereby CCR6 may mediated class switching to IgE, we enriched total B cells from healthy donor peripheral blood mononuclear cells and stimulated with 20ng/ml human IL-4 and 10μg/ml agnostic anti-human CD40 with or without 20ng/ml CCL20 for 3 days. After 3 days of treatment, cells were collected and stained with a 15-color panel and analyzed via flow cytometry. Cells were analyzed for surface expression of CD20 and CD3 to gate total B cells. Gated B cells were further separated into CD27+/IgM-/IgD- to define SWM B cell population. CCL20 treatment did not increase the total percent of SWM B cells; however, there was a 2-3-fold increase in CCR6+ SWM B cells compared to CCR6- SWM B cells. CCL20 treated CCR6+ SWM B cells have an average of 7% increase of phosphorylated mTOR in total SWM B cells compared to nonCCL20 treated CCR6+ SWM B cells. These results suggest CCL20 stimulation induces mTOR phosphorylation and activation. Thus, mTOR activation and downstream mediators may be necessary for α -gal induced B cell class switching. From these preliminary studies, we conclude that CCL20 stimulation increases the percent pmTOR+ SWM B cells. We will continue to investigate downstream mTOR mediators in regard to B cell class switching after CCL20 stimulation and how α-gal sensitization augments B cell IgE class switching and increases atherosclerosis with our novel α -gal-/- Apoe-/- mouse.

Combining advanced 3D printing technologies with origami principles: A new paradigm for the design of functional, durable, and scalable springs

Origami has recently emerged as a platform for building functional engineering systems with versatile characteristics that targeted niche applications. One widely utilized origami-based structure is known as the Kresling origami spring (KOS), which inspired, among many other things, the design of vibration isolators, fluidic muscles, and mechanical bit memory switches. Previous demonstrations of such concepts were carried out using paper-based KOSs, which are suitable for conceptual illustrations but not for implementation in a real environment. In addition to the very low durability resulting from the high plastic deformations at the paper folds; lack of repeatability, and high variation of performance among similar samples are also inevitable. To circumvent these issues, this paper presents a novel approach for the design of a non-paper based KOS, which mimics the qualitative behavior of the paper-based KOS without compromising on durability, repeatability, and functionality. In the new design, each fundamental triangle in the paper-based KOS is replaced by an inner central rigid core and an outer flexible rubber-like frame, which are fabricated out of different visco-elastic materials using advanced 3-D printing technologies. The quasi-static behavior of the fabricated springs was assessed under both compressive and tensile loads. It is shown that KOSs with linear, softening, hardening, mono- and bi-stable restoring force behavior can be fabricated using the proposed design by simple changes to the geometric design parameters, further pointing to the vast range of potential applications of such springs.

Ultrafast Threshold Switching Dynamics in Phase‐Change Materials

Discovery of electrical switching in chalcogenide glasses by S.R. Ovshinsky paves a new path for developing high‐speed nonvolatile electronic memory and high‐performance computing solutions. This article presents a review on the systematic understanding of threshold switching (TS) properties in various chalcogenide materials, Ovonic threshold switching (OTS) and Ovonic memory switching (OMS), the nature of TS, voltage‐dependent transient characteristics, and the role of TS in governing the programming speed based on research efforts over the last six decades. Furthermore, realization of TS in picosecond timescale, the commonalities between OTS and OMS, and the possible underlying mechanism has been explored. Furthermore, a scheme of material classification based on TS dynamics for ultrafast yet energy‐efficient programming has been proposed for phase‐change memory with SRAM‐like programming speed for future electronics.

Lung Transplant Recipients Developing Early DSAs within the First Month Are Characterized by a Higher Frequency of Naïve and a Lower Frequency of Memory B Cells

<h3>Purpose</h3> After lung transplantation (LuTx), the development of early donor-HLA-specific antibodies (eDSA) has been shown to be associated with antibody-mediated rejection (AMR) and poor graft survival. Since 2013, patients with eDSA within the first month after LuTx are treated with IgA/IgM-enriched intravenous immunoglobulins (IgGAM), in clinical AMR combined with anti-CD20 antibody (Rituximab). We hypothesize a different distribution and kinetics of IgD⁺CD27^- naïve B cells vs. IgD^-CD27^+/- memory B cell subsets in recipients with or without eDSA. <h3>Methods</h3> In a pilot study of 62 LuTx recipients, B cell subsets were by analyzed in blood pre, post (T0), 24 hours (T24) and 3 weeks after LuTx by flow cytometry using CD19, CD20, IgD, CD24, CD27, CD38 antibodies. Frequencies of B cell subsets were compared between two groups, eDSA-positive (n=14, 22,6%) and -negative (n=48, 77,4%) patients and healthy donors (n=30). <h3>Results</h3> Prior to LuTx, patients with end-stage lung disease showed significantly higher proprotions of IgD⁺CD27^- naïve B cells compared to HC (p<0.001). At T0, T1 and T24, patients with eDSAs showed significantly higher frequencies of naïve and lower frequencies of IgD^-CD27⁺ memory B cells (both p< 0.001) compared to eDSA-negative patients. These IgD⁺CD27^- naïve B cells displayed high CD24 and CD38 expression, which was stable also at 3 wks. A transient increase in IgD⁺CD27⁺ switch memory B cells was detected at T0 in both groups, returning to baseline levels at T24. <h3>Conclusion</h3> Lung transplant recipients show remarkable dynamics of naïve, memory and switch memory B cells within the first 3 wks. In both groups, we saw a shift in the B cell population: increased naïve B cells and decreased memory B cells, which was more pronounced in the eDSA group. Based on our preliminary data, a more refined B cell monitoring with additional markers may be able to identify patients with a higher risk for eDSA development. The impact of the treatment regimen on these B cell subsets is currently investigated.

Improved analog switching characteristics of Ta2O5-based memristor using indium tin oxide buffer layer for neuromorphic computing

A memristor is defined as a non-volatile memory switching two-terminal resistor, and a memristor with digital switching characteristics is widely studied as a next-generation non-volatile memory because of its simple structure, high integration density, and low power consumption. Recently, analog memristors with gradual resistance switching (RS) characteristics have garnered great attention because of their potential to implement artificial synapses that can emulate the brain functions. Transition metal oxides are thought to be strong candidate materials for the RS. In particular, tantalum oxide (TaO x )-based memristive devices provide stable and durable switching characteristics. TaO x -based memristors utilize analog switching characteristics and have excellent durability and reliability, so they can be applied as artificial synaptic device. In this study, the characteristics of analog RS using Ta2O5-based memristive devices were investigated. The current level of the Pt/Ta2O5/Pt memristors was improved by adjusting the thickness of Ta2O5. In particular, when an indium-tin-oxide (ITO) buffer layer was added to Ta2O5 forming a Pt/ITO/Ta2O5/Pt heterostructured double-layer device, it showed more symmetrical potentiation and depression characteristics under both polarities than a single-layer device without ITO layer. The symmetrical and linear potentiation and depression characteristics are essential for the development of efficient memristor-based neuromorphic systems. Insertion of the ITO buffer layer improves linearity, symmetry, and stability of the analog RS properties of Ta2O5-based memristors to artificial synapses.

Estimating the Switching phenomenon for Se98Te2 and Se96Te2X2 (X=Zn or Cd) Chalcogenide glasses.

The switching behavior was investigated for Se98Te2 and Se96Te2X2 (X= Zn or Cd) Chalcogenide glasses in thin film form. The thermal evaporation process was used for the preparation of the film samples. I−V curves were investigated in the thickness range (200-670 nm) and temperature range (293-318 K). The I−V curves show a memory switch. The values of threshold voltage (Vth) found to decrease with the addition of Zn and Cd to Se98Te2 respectively. Also, the threshold voltage (Vth) values decrease exponentially with increasing temperature and increase with thickness. The ratio between the threshold voltage activation energy Δεth and dc electrical activation energy ΔEσ for the studied compositions suggests the explanation of the switching process by the electrothermal model. The threshold electric field Eth values were obtained and show an inverse relation with temperature for our studied system. The effect of Cd and Zn addition to Se98Te2 on the obtained parameters was also explained.

Ultra-compact nonvolatile plasmonic phase change modulators and switches with dual electrical–optical functionality

Programmable photonic integrated circuits (PICs) are the foundation of on-chip optical technologies, with the optical modulators being one of the main building blocks of such programmable PICs. However, most of the available modulators suffer from high power consumption, low response time, and large footprint. Additionally, they show a large resistance modulation; thus, they require high switching voltage. In consequence, they operate much above CMOS-compatible voltages of 1.2 V and with high insertion losses. Furthermore, the state and information they carry are lost once the power is turned off—so, they are volatile. Thus, realizing modulators and phase shifters that overcome all those problems still remains a challenge. To overcome some of those limitations, the nonvolatile phase change materials implemented in the plasmonic structures are proposed that can offer many advantages as result of high electric field interaction with nonvolatile materials. Consequently, novel plasmonic nonvolatile switches proposed here can operate by phase modulation, absorption modulation, or both and under zero-static power. For the first time, the nonvolatile phase modulator is proposed that requires only 230 nm long active waveguide to attain full π phase delay with an insertion loss below even 0.12 dB. Simultaneously, under the requirements, it can operate as an amplitude modulator with an extinction ratio exceeding 2.2 dB/μm while the insertion losses are kept below 0.185 dB/μm. Furthermore, the heating mechanism can be based on the external heaters, internal heaters, electrical (memory) switching, or optical switching mechanism, which provide a lot of flexibility in terms of a design and requirements.

Content-Addressable Memory System Using a Nanoelectromechanical Memory Switch

Content-addressable memory (CAM) performs a parallel search operation by comparing the search data with all content stored in memory during a single cycle, instead of finding the data using an address. Conventional CAM designs use a dynamic CMOS architecture for high matching speed and high density; however, such implementations require the use of system clocks, and thus, suffer from timing violations and design limitations, such as charge sharing. In this paper, we propose a static-based architecture for a low-power, high-speed binary CAM (BCAM) and ternary CAM (TCAM), using a nanoelectromechanical (NEM) memory switch for nonvolatile data storage. We designed the proposed CAM architectures on a 65 nm process node with a 1.2 V operating voltage. The results of the layout simulation show that the proposed design has up to 23% less propagation delay, three times less matching power, and 9.4 times less area than a conventional design.

Spring blooms from self-assembly: epigenetic memory governed by nuclear assemblies and condensates

While trimethylated marks on histone H3K27 encode silenced epigenetic memory states, these alone have been proposed to be insufficient to retain functional memory and state switching over many cell cycles. FLOWERING LOCUS C (FLC) in Arabidopsis thaliana is one such locus silenced by H3K27me3, and which governs the critical timing of flowering after winter cold. Such vernalization silencing at FLC requires the cold-promoted protein VIN3 and the Polycomb accessory protein VRN5. Using single-molecule Slimfield tracking in the living root, we reveal nuclear assemblies of each of VIN3 and VRN5 throughout vernalization.

Effects of Ambient and Annealing Temperature in HfO2 Based RRAM Device Modeling and Circuit-Level Implementation

This article focuses on the relevance of the effect of ambient temperature and annealing in the context of compact modeling of metal oxide resistive random access memory (RRAM) devices. The ambient temperature affects the conduction characteristic of resistive switching memories, so it becomes an essential factor to include when adjusting the experimental data. Reported the fabricated results and memory switching parameters with the defined set (Vset) and reset (Vreset) transition voltages for the fabricated annealed HfO2-based RRAM. Additionally, to illustrate the importance of this characteristic in the form of the I-V curve, the Stanford model (SFM) for RRAM devices is enhanced by incorporating the annealing temperature as an additional parameter in the script of the Verilog-A model. Stanford and modified Stanford model (MSFM) are analyzed at the device level using cadence circuit simulator and implemented in the nonvolatile memory circuit (3 *3 memory arrays). Results confirmed that the experimental switching voltages, Vset, Vreset are 1.7 V, −0.8 V. These values are well suited along the simulated MSFM switching voltages of, Vset, Vreset (1.8 V, −0.7 V). The mean error percentage of the MSF is 18.42%.

Optimizing Ferroelectric and Interface Layers in HZO-Based FTJs for Neuromorphic Applications

Nonvolatile memories especially the ferroelectric (FE)-based ones such as ferroelectric tunnel junctions (FTJs) and ferroelectric field-effect transistors (FeFETs) have recently attracted a lot of attention. FTJs have been intensively researched for the last decade and found to be very promising memory devices due to their significant nondestructive readout advantage as compared to conventional ferroelectric random access memory (FRAM). However, more research is needed on FTJ devices to obtain reliable endurance and retention behavior. In this article, we demonstrate the characteristics and performance of zirconium-doped hafnium oxide-based FTJ devices in terms of FE switching and reliability. This is investigated for FTJ stack structure tuning as well as for the FE switching process in FTJ devices. The FTJ memory switching characteristics, the effects of polarization switching on the write conditions, and the impact of pulse width and pulse amplitude on switching are investigated. The impact of FE layer thickness and interface layer type/thickness are reported to obtain a maximum FTJ <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio (memory window) and reliable performance. The maximum <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio changes depending on the FE layer (zirconium-doped HfO₂ layer) thickness (12, 8, 6, and 4 nm), the interface layer type (SiO₂, Al₂O₃), and thickness (1 and 2 nm), indicating the maximum value of <inline-formula> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio for a 1 nm SiO₂ interface layer stack. Moreover, a stable endurance of 10⁴ cycles is reported and extrapolated measurements suggest stable retention for more than ten years. Time-dependent breakdown analysis was performed to investigate the reliability of devices indicating a lifetime of ten years.

Facile Achievement of Complementary Resistive Switching in Block Copolymer Micelle-Based Resistive Memories.

Interest in resistive random access memory (RRAM) has grown rapidly in recent years for realizing ultrahigh density data storage devices. However, sneak currents in these devices can result in misreading of the data, thus limiting the applicability of RRAM. Complementary resistive switching (CRS) memory consisting of two antiserial RRAMs can considerably reduce sneak currents; however, complicated device architectures and manufacturing processes still remain as challenges. Herein, an effective and simple approach for fabricating CRS memory devices using self-assembled block copolymer micelles is reported. Cu ions are selectively placed in the core of polystyrene-block-poly(2-vinylpyridine) spherical micelles, and a hexagonally packed micelle monolayer is prepared through spin-coating. The micelle monolayer can be a symmetrical resistive switching layer, because the micelles and Cu act as dielectric and active metals in memory devices, respectively. The locally enhanced electric field and Joule heating achieved by the structured Cu atoms inside the micelles promote metal ionization and ion migration in a controlled manner, thus allowing for position selectivity during resistive switching. The micelle-based memory device exhibits stable and reliable CRS behavior, with a nonoverlapping and narrow distribution of threshold voltages. Therefore, this approach is promising for fabricating CRS memory devices for high-performance and ultrahigh-density RRAM applications.

Are CDS spreads predictable during the Covid-19 pandemic? Forecasting based on SVM, GMDH, LSTM and Markov switching autoregression

This paper investigates the forecasting performance for credit default swap (CDS) spreads by Support Vector Machines (SVM), Group Method of Data Handling (GMDH), Long Short-Term Memory (LSTM) and Markov switching autoregression (MSA) for daily CDS spreads of the 513 leading US companies, in the period 2009–2020. The goal of this study is to test the forecasting performance of these methods before and during the Covid-19 pandemic and to check whether there are changes in the market efficiency. MSA outperforms all other methods most frequently. GMDH breaks the efficient market hypothesis more frequently (75%) than other methods. The change of the relative predictability during Covid-19 is small with some increase of the advantage of the investigated methods over a benchmark. We find that the market has been less efficient during Covid-19, however, there are no huge differences in prediction performances before and during the Covid-19 period.

Artificial Neurons and Synapses Based on Al/a-SiNxOy:H/P+-Si Device with Tunable Resistive Switching from Threshold to Memory.

As the building block of brain-inspired computing, resistive switching memory devices have recently attracted great interest due to their biological function to mimic synapses and neurons, which displays the memory switching or threshold switching characteristic. To make it possible for the Si-based artificial neurons and synapse to be integrated with the neuromorphic chip, the tunable threshold and memory switching characteristic is highly in demand for their perfect compatibility with the mature CMOS technology. We first report artificial neurons and synapses based on the Al/a-SiNxOy:H/P+-Si device with the tunable switching from threshold to memory can be realized by controlling the compliance current. It is found that volatile TS from Al/a-SiNxOy:H/P+-Si device under the lower compliance current is induced by the weak Si dangling bond conductive pathway, which originates from the broken Si-H bonds. While stable nonvolatile MS under the higher compliance current is attributed to the strong Si dangling bond conductive pathway, which is formed by the broken Si-H and Si-O bonds. Theoretical calculation reveals that the conduction mechanism of TS and MS agree with P-F model, space charge limited current model and Ohm’s law, respectively. The tunable TS and MS characteristic of Al/a-SiNxOy:H/P+-Si device can be successfully employed to mimic the biological behavior of neurons and synapse including the integrate-and-fire function, paired-pulse facilitation, long-term potentiation and long-term depression as well as spike-timing-dependent plasticity. Our discovery supplies an effective way to construct the neuromorphic devices for brain-inspired computing in the AI period.

Switching, Raman and morphological studies on Si20Te74Sn6 chalcogenide glass

Chalcogenide materials are getting lot of research attention due to their ability to switchfrom an amorphous to a crystalline phase with lower threshold voltage which is a primary requirement for fabricating phase-change memory. Here we have prepared the Si20Te74Sn6 bulk sample using melt quenching technique. It has been observed that the sample exhibits a memory switching phenomenon with the addition of Sn dopant on Si-Te base glasses. Memory switching is mainly observed due to Te rich host matrix and the metallicity of Sn dopant. The sample exhibits a linear variation of threshold voltage with an increase in thickness, which is compatible with memory switching behaviour. Raman studies on as-quenched Si20Te74Sn6 glass are carried out to study the structural behaviour of the network. The observed Raman peaks are attributed to crystalline tellurium and the vibrational modes of Sn/Si lattice. Morphological studies on switched and un-switched samples using SEM reveal a structural alteration in the switched region, which can also be related to the creation of conducting channel between two electrodes during memory switching.

Host-Guest Synergy of Ch3nh3pbbr3@Ln-Mofs Enabling Tunable Green Luminescence and Switchable Memory

Host-Guest Synergy of Ch3nh3pbbr3@Ln-Mofs Enabling Tunable Green Luminescence and Switchable Memory

In-Memory Nearest Neighbor Search With Nanoelectromechanical Ternary Content-Addressable Memory

Nearest neighbor (NN) search is widely used in pattern classification and memory-augmented neural networks. To overcome the von Neumann bottleneck in conventional NN search architecture, in this study, nanoelectromechanical-switch-based ternary content-addressable memory (NEMTCAM) is introduced for the NN classifier. NEMTCAM can calculate the Hamming distance between the input vector and the stored vectors in a parallel search operation. The NEMTCAM operation was experimentally demonstrated. Furthermore, an analytical model for NN search accuracy, including cell-to-cell parasitic resistance, is presented. NEMTCAM can calculate up to 10 Hamming distances in 32-bit words owing to the high current ratio of the NEM memory switches.

Evidence for a Specific Association Between Sustained Attention and Gait Speed in Middle-to-Older-Aged Adults

Although cognitive decline has previously been associated with mobility limitations and frailty, the relationship between sustained attention and gait speed is incompletely characterized. To better quantify the specificity of the sustained attention and gait speed association, we examined the extent to which this relationship is unique rather than accounted for by executive functioning and physical health characteristics. 58 middle-to-older-aged community-dwelling adults without overt illness or diseases (45-90 years old, 21 females) participated in the study. Each participant completed a 4-meter gait speed assessment and validated neuropsychological tests to examine various domains of executive functions including working memory (i.e., Digit Span), inhibitory control (i.e., Stroop Color Word Test), and task switching (i.e., Trail Making Test). Multiple physical and vascular risk factors were also evaluated. Sustained attention was assessed using the gradual onset continuous performance task (gradCPT), a well validated go/no-go sustained attention task. A series of linear regression models were created to examine how different aspects of cognition, including sustained attention and traditional measures of executive functioning, related to gait speed while controlling for a variety of physical and vascular risk factors. Among all predictors, gradCPT accuracy explained the most variance in gait speed (R2 = 0.21, p < 0.001) and was the only significant predictor (β = 0.36, p = 0.01) when accounting for executive functioning and other physical and vascular risk factors. The present results indicate that sustained attention may be uniquely sensitive and mechanistically linked to mobility limitations in middle-to-older adults.

Boosted Electronic, NLO and Absorption Characteristics for Quercetin and Taxifolin; Comparative Experimental and DFT Studies

In the present study, a considerable, reproducible, and eco-friendly biological synthesis of Ag nanoparticles using Mangifera indica leaf extract as a reductant is documented. The spectroscopic characteristics of synthesized Ag nanoparticles are described by both UV-Vis and FT-IR techniques. The bandgap offsets, reactivity, and NLO properties for two flavonoids, quercetin, and taxifolin, are examined using the DFT approach. Also, a detailed comparative analysis for HOMO-LUMO interactions among quercetin and taxifolin is discussed. Results show that quercetin and taxifolin possess dipole moment (DM=4.79, 3.99 Debye) and bandgap offset (2.59, 2.98 eV). Both molecules are promising candidates as window layers for solar cells and memory switch devices. In addition, hyperpolarizability calculations show that quercetin NLO response is higher than taxifolin, which sets a revolutionary recall for NLO manufacture upgrade. Moreover, NBO and UV-Vis absorption characteristics are reported as well.

Boosted Electronic, NLO and Absorption Characteristics for Quercetin and Taxifolin: Comparative Experimental and DFT Studies

In the present study, a considerable, reproducible, and eco-friendly biological synthesis of Ag nanoparticles using Mangifera indica leaf extract as a reductant is documented. The spectroscopic characteristics of synthesized Ag nanoparticles are described by both UV-Vis and FT-IR techniques. The bandgap offsets, reactivity, and NLO properties for two flavonoids, quercetin, and taxifolin, are examined using the DFT approach. Also, a detailed comparative analysis for HOMO-LUMO interactions among quercetin and taxifolin is discussed. Results show that quercetin and taxifolin possess dipole moment (DM=4.79, 3.99 Debye) and bandgap offset (2.59, 2.98 eV). Both molecules are promising candidates as window layers for solar cells and memory switch devices. In addition, hyperpolarizability calculations show that quercetin NLO response is higher than taxifolin, which sets a revolutionary recall for NLO manufacture upgrade. Moreover, NBO and UV-Vis absorption characteristics are reported as well.