Memory Bits Research Articles

Microscopic theory of spin relaxation of a single Fe adatom coupled to substrate vibrations

Understanding the spin-relaxation mechanism of single adatoms is an essential step towards creating atomic magnetic memory bits or even qubits. Here we present an essentially parameter-free theory by combining \textit{ab-initio} electronic and vibrational properties with the many-body nature of atomic states. Our calculations account for the millisecond spin lifetime measured recently on Fe adatoms on MgO/Ag(100) and reproduce the dependence on the number of decoupling layers and the external magnetic field. We show how the atomic interaction with the environment should be tuned in order to enhance the magnetic stability, and propose a clear fingerprint for experimentally detecting a localized spin-phonon excitation.

Origami-based integration of robots that sense, decide, and respond

Origami-inspired engineering has enabled intelligent materials and structures to process and react to environmental stimuli. However, it is challenging to achieve complete sense-decide-act loops in origami materials for autonomous interaction with environments, mainly due to the lack of information processing units that can interface with sensing and actuation. Here, we introduce an integrated origami-based process to create autonomous robots by embedding sensing, computing, and actuating in compliant, conductive materials. By combining flexible bistable mechanisms and conductive thermal artificial muscles, we realize origami multiplexed switches and configure them to generate digital logic gates, memory bits, and thus integrated autonomous origami robots. We demonstrate with a flytrap-inspired robot that captures ‘living prey’, an untethered crawler that avoids obstacles, and a wheeled vehicle that locomotes with reprogrammable trajectories. Our method provides routes to achieve autonomy for origami robots through tight functional integration in compliant, conductive materials.

Online Digital Implementation of Wide Voltage Range RMS-Current-Optimized Control With Voltage Balancing Capability for DAB Converter

The dual active bridge (DAB) converter is widely used in renewable energy power generation systems with wide input voltage characteristics. An inappropriate duty cycle will lead to a larger inductor RMS current and low efficiency. In this paper, an efficiency-oriented optimized triple-phase-shift (OTPS) scheme is proposed for the dual active bridge (DAB) converter that can reduce the inductor root-mean-square (RMS) current for a wide input voltage and realize zero voltage switching (ZVS). The ZVS condition contains the direction and amplitude of the inductor current to make the ZVS area more accurate. In addition, the OTPS scheme also has the capability of voltage balancing without additional voltage equalizers under unbalanced load. The influence of deadtime on voltage balance is analyzed and a voltage balancing scheme with compensation of the duty cycle is proposed. To reduce resource occupation and operation time, an on-line implementation scheme of variable parameter control (VPC) based on field programable gate array (FPGA) is proposed. Without a look-up table, the sum of the operation time of the control module and modulation module is only 0.66 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> s, and the required memory bits are only 459k. Both operation time and memory bits are reduced by more than 90% compared to existing literature. Finally, the whole proposed process is verified by the experimental results.

A Craft Essay on Trauma

A Craft Essay on Trauma

Bit-complexity of classical solutions of linear evolutionary systems of partial differential equations

We study the bit-complexity intrinsic to solving the initial-value and (several types of) boundary-value problems for linear evolutionary systems of partial differential equations (PDEs), based on the Computable Analysis approach. Our algorithms are guaranteed to compute classical solutions to such problems approximately up to error 1/2n, so that n corresponds to the number of reliable bits of the output; bit-cost is measured with respect to n. Computational Complexity Theory allows us to prove in a rigorous sense that PDEs with constant coefficients are algorithmically ‘easier’ than general ones. Indeed, solutions to the latter are shown (under natural assumptions) computable using a polynomial number of memory bits, and we prove that the complexity class PSPACE is in general optimal; while the case of constant coefficients can be solved in #P—also essentially optimally so: the Heat Equation ‘requires’ #P1. Our algorithms raise difference schemes to exponential powers, efficiently: we compute any desired entry of such a power in #P, provided that the underlying exponential-sized matrices are circulant of constant bandwidth. Exponentially powering modular two-band circulant matrices is established even feasible in P; and under additional conditions, also the solution to certain linear PDEs becomes polynomial time computable.

Solvent-Induced Degradation of Electrochemically Exfoliated Vanadium Selenide Visualized by Electron Microscopy.

Recently discovered two-dimensional ferromagnetic materials (2DFMs) have rapidly gained much interest in the fields of spintronics and computing, where they may prove powerful tools for miniaturizing devices such as magnetic tunnel junctions and spin-transfer torque memory bits. In addition, heterojunctions and twisted bilayer stacks of such materials may yield exotic spin textures. However, preparation of such devices is complicated by the air sensitivity of many 2DFMs. Here, we report details on the preparation of few-to-monolayer flakes of vanadium selenide (VSe2) using electrochemical exfoliation in propylene carbonate. We also present a detailed study of the effects of air on the structure and magnetic properties of bare and passivated VSe2 after different concentrations of surface passivation treatment. We characterized the microstructure of holes in the VSe2 flakes and the formation of new compounds arising from air exposure, solvent exposure during the exfoliating process, and deliberate electron beam irradiation (sculpting). We sculpt VSe2 flakes while retaining the 1T-VSe2 lattice structure, opening the door for top-down patterned high-resolution 2DFM nanostructures. Additionally, investigation of the magnetic response of nanosheets using magnetic force microscopy (MFM) showed that the oxidation-induced damage only affects the surface fields locally and does not quench large-scale magnetic signal. The findings of this study pave the way toward practical incorporation of 2D ferromagnetic materials in nanoelectronics.

Five-Direction Occlusion Filling with Five Layer Parallel Two-Stage Pipeline for Stereo Matching with Sub-Pixel Disparity Map Estimation.

Binocular stereoscopic matching is an essential method in computer vision, imitating human binocular technology to obtain distance information. Among plentiful stereo matching algorithms, Semi-Global Matching (SGM) is recognized as one of the most popular vision algorithms due to its relatively low power consumption and high accuracy, resulting in many excellent SGM-based hardware accelerators. However, vision algorithms, including SGM, are still somewhat inaccurate in actual long-range applications. Therefore, this paper proposes a disparity improvement strategy based on subpixel interpolation and disparity optimization post-processing using an area optimization strategy, hardware-friendly divider, split look-up table, and the clock alignment multi-directional disparity occlusion filling, and depth acquisition based on floating-point operations. The hardware architecture based on optimization algorithms is on the Stratix-IV platform. It consumes about 5.6 K LUTs, 12.8 K registers, and 2.5 M bits of on-chip memory. Meanwhile, the non-occlusion error rate of only 4.61% is about 1% better than the state-of-the-art works in the KITTI2015 dataset. The maximum working frequency can reach up to 98.28 MHz for the 640 × 480 resolution video and 128 disparity range with the power dissipation of 1.459 W and 320 frames per second processing speed.

A Cube Attack on a Reduced-Round Sycon

The cube attack was proposed at the 2009 Eurocrypt. The attack derives linear polynomials for specific output bits of a BlackBox cipher. Cube attacks target recovery keys or secret states. In this paper, we present a cube attack on a 5-round Sycon permutation and a 6-round Sycon permutation with a 320-bit state, whose rate occupies 96 bits, and whose capacity is 224 bits. We found cube variables related to a superpoly with a secret state. Within the cube variables, we recovered 32 bits of the secret state. The target algorithm was Sycon with 5-round and 6-round versions of permutation. For the 5-round Sycon, we found a cube variable and recovered a state with a total of 2192 Sycon computations and 237 bits of memory. For the 6-round Sycon, we found cube variables and recovered a state with a total of 2192 Sycon computations and 270 bits of memory. When using brute force in a 5-round attack, 2224 operations were required, but the cube attack proposed in this paper had 248 offline operations, and 232 operations were required. When using brute force in a 6-round attack, 2224 operations were required, but the cube attack proposed in this paper required 295 offline operations, and 263 operations were required. For both attacks, offline could be used continuously after performing only once. To the best of our knowledge, this is the first cube attack on Sycon.

Entangled polarizations in ferroelectrics: A focused review of polar topologies

Ferroelectric crystals feature asymmetric or polar structures that are switchable under an external electric field, holding promise for information storage. Nanoscale ferroelectrics might exhibit various exotic domain configurations and polar topologies, such as full flux-closure, vortex, skyrmion, and meron. These topological domains were theoretically switchable and may give rise to an unusually high density of memory bits. They would also undergo unusual phase transitions and form hidden, collective polar topological states under external stimulations. Similar domains and spin topologies are well known in ferromagnetic materials, and their topological properties and dynamics are under intensive investigation. However, in ferroelectric materials, the coupling of polarizations to spontaneous strains would be so pronounced that the formations of polar topologies were believed to be impossible. How to stabilize the polar topologies in ferroelectrics, especially in nanoscale ferroelectrics, was known as a big challenge.In this overview, we summarize the recent progress in polar topologies in ferroelectric oxides. We start from a review the discovery of polar topologies, including flux-closure quadrant, vortex, bubble, skyrmion, meron lattice, polar waves, and center-type domains. We also focus on the effects of mechanical and electrical boundary conditions and sample size on the formation of topological structures. In the meanwhile, we emphasize the use of aberration-corrected transmission electron microscope which enables to visualize the ion displacement at a sub-Ångström resolution in real space. And at the end, we envision several aspects to be considered in the future, such as imaging three dimensional (3D) atomic morphology of the topological polar structures, exploring novel polar topologies in other possible systems, and addressing the coupling of polar topologies with flexoelectricity by a combination of quantitative transmission electron microscopy and relevant theoretical approaches.

Reliability improved dual driven feedback 10T SRAM bit cell

This paper presents a dual driven feedback 10T (DDFB10T) static random-access memory (SRAM) bit cell with good read and write stability and that is free from half select issue. This DDFB10T cell working at VDD = 0.9 V achieves 1.5× higher static voltage noise margin (SVNM), and 0.48× lesser write trip voltage (WTV) than 6T SRAM cell. Monte Carlo simulation employing local and global variation using Cadence Virtuoso tool with 45 nm technology proves that the proposed bit cell is highly immune against process, voltage, and temperature (PVT) variations. The proposed DDFB10T bit cell exhibits lesser SVNM variability when it is normalized to that of 6T SRAM bit cell. The proposed DDFB10T cell is designed with the capability to provide a bit interleaved architecture for reducing half select issues.

A comparative radiation analysis of reconfigurable memory technologies: FinFET versus bulk CMOS

This work describes a comparative radiation reliability analysis between two reconfigurable devices with different manufacturing technology: 28 nm CMOS-based and 16 nm FinFET based FPGAs. The analysis is based on a proton radiation test campaign performed at the PSI radiation facility. As application circuit, a multi-core computational engine was implemented on each one of the reconfigurable devices. The radiation sensitivity has been reported in terms of the SEU cross-section of the configuration memory bits. Results have shown a higher sensitivity of 28 nm CMOS with respect to 16 nm FinFET. Moreover, a detailed comparison of detected Single Event Multiple Upsets (SEMUs) clusters for both technology is reported.

A Microring as a Reservoir Computing Node: Memory/Nonlinear Tasks and Effect of Input Non-Ideality

The nonlinear response of an optical microresonator is used in a time multiplexed reservoir computing neural network. Within a virtual node approach combined with an offline training through ridge regression, we solved linear and nonlinear logic operations. We analyzed the nonlinearity of the microresonator as a memory between bits and/or as a neural activation function. This is made possible by controlling both the distance between bits subject to the logical operation and the number of bits supplied to the ridge regression. We show that the optical microresonator exhibits up to two bits of memory in linear tasks and that it allows solving nonlinear tasks providing both memory and nonlinearity. Finally, we demonstrate that the virtual node approach always requires a comparison of the reservoirs performance with the results obtained by applying the same training process on the input signal.

Topological Charge Control of Skyrmion Structure in Frustrated Magnets by Circularly Polarized Light

The classical Heisenberg model with the ${J}_{1}$-${J}_{2}$-${J}_{3}$ interaction forms a skyrmion structure, which is characterized by quantized topological charge. Due to the symmetric interaction, the generated topological charges are randomly distributed in the system, and not controllable intrinsically. Here we show theoretically that manipulation of topological charge can be carried out by applying circularly polarized light, as a result of the mechanism of the topological inverse Faraday effect arising from the coupling of light helicity and topological charge. The effect is expected to be useful for control of the topological charge bit in a skyrmion-based racetrack memory.

The Big Match with a Clock and a Bit of Memory

The Big Match is a multistage two-player game. In each stage, player 1 hides one or two pebbles in his hand, and his opponent has to guess that number. Player 1 loses a point if player 2 is correct; otherwise, he wins a point. As soon as player 1 hides one pebble, the players cannot change their choices in any future stage. The undiscounted Big Match has been much-studied. Blackwell and Ferguson (1968) give an [Formula: see text]-optimal strategy for player 1 that hides, in each stage, one pebble with a probability that depends on the entire past history. Any strategy that depends on just the clock or just a finite memory is worthless (i.e., cannot guarantee strictly more than the least reward). The long-standing natural open problem has been whether every strategy that depends on just the clock and a finite memory is worthless. The present paper proves that there is such a strategy that is [Formula: see text]-optimal. In fact, we show that just two states of memory are sufficient.

An optimised hardware architecture of the angular-domain cyclostationary detector for cognitive radio communications

This paper proposes a novel method to improve the performance and reduce the implementation design complexity of the angular domain cyclostationary feature detection (CFD). This method implements Orthogonal Frequency Division Multiplexing (OFDM) signal detection for cognitive radio applications. The originality of this work is based on using a selective sampling process for the OFDM signal detection by using only samples related to the cyclic prefix (CP). Using only the first NCP (CP length) angles of the angular domain cyclic autocorrelation function and eliminating the remaining angles has significantly improved the detector sensitivity. Results from Matlab simulations revealed that the proposed method reaches a detection probability of 100% at an SNR (signal-to-noise ratio) equal to −16 dB in the case of an additive white Gaussian noise (AWGN) channel. Moreover, the proposed method outperforms the other CFD methods with a performance range up to 5 dB. The proposed algorithm is coded using the VHDL language and implemented with the minimum of counters and comparators on Field-programmable gate array (FPGA) platform without using multipliers and DSP blocks. The proposed design requires a lesser power, logic and memory bits by 5.95, 60.96 and 87.5%, respectively, compared to the conventional angular domain CFD design. The proposed hardware architecture can be more efficient for spectrum sensing in many communication systems, such as LTE-Advanced and the L-band Digital Aeronautical Communication System (LDACS).

Micro-magnetoelastic modeling of Terfenol-D for spintronics

This article focuses on computational studies evaluating the influence of crystallinity, residual stresses, and out-of-plane (OOP) deterministic switching on Terfenol-D nano/microstructures. The computational models use both coupled and uncoupled Landau–Liftshitz–Gilbert equations with elastodynamics to study strain-induced magnetization reorientation. A Voronoi tessellation approach models the crystal distribution in the microstructures subjected to residual stresses with good agreement to experimental data including large changes in coercivity values, i.e., from 100 to 3000 Oe. Parametric studies show how the coercivity is manipulated with residual stresses, including a magnetoelastically induced perpendicular-magnetic-anisotropy (PMA), important for memory applications. Additional parametric studies focus on epitaxially deposited micro-disks, revealing that residual stresses can create magnetoelastically dominant easy axes along the ⟨110⟩ directions, which are energetically favorable relative to the intrinsic ⟨111⟩ magnetocrystalline easy axes. Modification of the global easy axis is used to design a strain-mediated multiferroic composite consisting of a 20 nm epitaxially deposited Terfenol-D memory bit with PMA grown on a PZT substrate. The multiferroic disk achieves OOP deterministic clocking with an applied voltage.

Positional Stability of Skyrmions in a Racetrack Memory with Notched Geometry

Magnetic skyrmions are chiral spin textures with attractive features, such as ultra-small size, solitonic nature, and easy mobility with small electrical currents that make them promising as information-carrying bits in low-power high-density memory, and logic applications. However, it is essential to guarantee the positional stability of skyrmions for reliable information extraction. Using micromagnetic simulations for the minimum energy path (MEP), we compute the energy barriers associated with stabilizing notches along a racetrack. We vary material parameters, specifically, the strength of the chiral Dzyaloshinskii-Moriya interactions (DMI), the notch geometry, and the thickness of the racetrack to get the optimal barrier height. We find that the reduction of skyrmion size as it squeezes past the notch gives rise to the energy barrier. We find a range of energy barriers up to ~ 45 kBT for a racetrack of 5 nm thickness that can provide years long positional lifetime of skyrmions for long-term memory applications while requiring a moderate amount of current (~ 10^10 A/m2) to move the skyrmions. Furthermore, we derive quasi-analytical equations to estimate the energy barrier. We also explore other pinning mechanisms, such as a local variation of material parameters in a region, and find that notched geometry provides the highest energy barrier. Our results open up possibilities to design practical skyrmion-based racetrack geometries for spintronics applications.

Adaptive One Memory Access Bloom Filters

Bloom filters are widely used to perform fast approximate membership checking in networking applications. The main limitation of Bloom filters is that they suffer from false positives that can only be reduced by using more memory. We suggest to take advantage of a common repetition in the identity of queried elements to adapt Bloom filters for avoiding false positives for elements that repeat upon queries. In this paper, one memory access Bloom filters are used to design an adaptation scheme that can effectively remove false positives while completing all queries in a single memory access. The proposed filters are well suited for scenarios on which the number of memory bits per element is low and thus complement existing adaptive cuckoo filters that are not efficient in that case. The evaluation results using packet traces show that the proposed adaptive Bloom filters can significantly reduce the false positive rate in networking applications with the single memory access. In particular, when using as few as four bits per element, false positive rates below 5% are achieved.

TCAM Network Memory Error Detection and Correction Method

Ternary content addressable memories (TCAMs) are widelyused in network devices to implement packet classification. They are used, for example, for packet forwarding, for security, and to implement software-defined networks (SDNs). TCAMs are commonly implemented as standalone devices or as an intellectual property block that is integrated on networking application-specific integrated circuits. On the other hand, field-programmable gate arrays (FPGAs) do not include TCAM blocks. However, the flexibility of FPGAs makes them attractive for SDN implementations, and most FPGA vendors provide development kits for SDN. Those need to support TCAM functionality and, therefore, there is a need to emulate TCAMs using the logic blocks available in the FPGA. In recent years, a number of schemes to emulate TCAMs on FPGAs have been proposed. Some of them take advantage of the large number of memory blocks available inside modern FPGAs to use them to implement TCAMs. A problem when using memories is that they can be affected by soft errors that corrupt the stored bits. The memories can be protected with a parity check to detect errors or with an error correction code to correct them, but this requires additional memory bits per word. In this brief, the protection of the memories used to emulate TCAMs is considered. In particular, it is shown that by exploiting the fact that only a subset of the possible memory contents are valid, most single-bit errors can be corrected when the memories are protected with a parity bit.

Bird Cottage

Bird Cottage