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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Sparse Data Acquisition on Emerging Memory Architectures

Emerging memory devices, such as resistive crossbars, have the capacity to store large amounts of data in a single array. Acquiring the data stored in large-capacity crossbars in a sequential fashion can become a bottleneck. We present practical methods, based on sparse sampling, to quickly acquire sparse data stored on emerging memory devices that support the basic summation kernel, reducing the acquisition time from linear to sub-linear. Experimental results show that at least an order of magnitude improvement in acquisition time can be achieved when the data is sparse.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Autonomous Multistate Nanoencoding Using Combinatorial Ferroelectric Closure Domains in BiFeO 3

Recent advances in ferroic materials have identified topological defects as promising candidates for enabling additional functionalities in future electronic systems. The generation of stable and customizable polar topologies is needed to achieve multistates that enable beyond-binary device architectures. Here, in this study, we show how to autonomously pattern on-demand highly tunable striped closure domains in pristine rhombohedral-phase BiFeO 3 thin films through precise scanning of a biased atomic force microscopy tip along carefully designed paths. By employing this strategy, we generate and manipulate closed-loop structures with high spatial resolution in an automated manner, allowing the creation of highly tunable and intricate topological domain structures that exhibit distinct polarization configurations without the need for electrode deposition or complex heterostructure growth. As a proof-of-concept for ferroelectric beyond-binary memory devices, we use such topological domains as multistates, engineering an alphabet and automating the symbolic writing/reading process using autonomous microscopy. The resulting information density is compared with that of current commercially available memory devices, demonstrating the potential of ferroelectric topological domains for multistate information storage applications.

BiFeO3↗
DOE OSTI2014

Store-operate-coherence-on-value

A system, method and computer program product for performing various store-operate instructions in a parallel computing environment that includes a plurality of processors and at least one cache memory device. A queue in the system receives, from a processor, a store-operate instruction that specifies under which condition a cache coherence operation is to be invoked. A hardware unit in the system runs the received store-operate instruction. The hardware unit evaluates whether a result of the running the received store-operate instruction satisfies the condition. The hardware unit invokes a cache coherence operation on a cache memory address associated with the received store-operate instruction if the result satisfies the condition. Otherwise, the hardware unit does not invoke the cache coherence operation on the cache memory device.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Implementing the OpenACC Data Model

Programming accelerators today usually requires managing separate virtual and physical memories, such as allocating space in and copying data between host and device memories. The OpenACC API provides data directives and clauses to control this behavior where it is required. This paper describes how the data model is supported in current OpenACC implementations, ranging from research compilers (OpenUH and OpenARC) to a commercial compiler (the PGI OpenACC compiler). This includes implementation of the data directives and clauses, testing whether the data is already present on the device, OpenCL support, managing asynchronous data transfers and memory allocations, handling aliased data, reusing device memory, managing partially present data, and support for shared memory between host and device. Lastly, it also discusses on-going work to manage large, complex dynamic data structures.

Wolfe, Michael↗
DOE OSTI2025

A new era of ferroelectric thin films for nonvolatile memories

Ferroelectric films have potential applications in nonvolatile memory devices. In addition to the well-established perovskite-structure oxide ferroelectrics, hafnia- and wurtzite-based ferroelectrics have recently attracted considerable attention because of the improved scalability of the ferroelectric response (down to nanometer thicknesses), their compatibility with silicon fabrication processes, and the availability of deposition methods that realize three-dimensional structures. Furthermore, due to their high compatibility with silicon processes, these are also expected to be used in emerging energy-efficient applications, such as neuromorphic computing and reservoir computing. In this article, we review the fundamentals of hafnia- and wurtzite-based ferroelectrics and their advantages and issues for developing in nonvolatile memory devices. Then, possible emerging applications are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Heap/stack guard pages using a wakeup unit

A method and system for providing a memory access check on a processor including the steps of detecting accesses to a memory device including level-1 cache using a wakeup unit. The method includes invalidating level-1 cache ranges corresponding to a guard page, and configuring a plurality of wakeup address compare (WAC) registers to allow access to selected WAC registers. The method selects one of the plurality of WAC registers, and sets up a WAC register related to the guard page. The method configures the wakeup unit to interrupt on access of the selected WAC register. The method detects access of the memory device using the wakeup unit when a guard page is violated. The method generates an interrupt to the core using the wakeup unit, and determines the source of the interrupt. The method detects the activated WAC registers assigned to the violated guard page, and initiates a response.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1987

Rare-earth substitution in (BiYCa)3(FeSiGe)5O12 bubble films

The substitution of Y by Sm, Tb, Gd, and Ho in (BiYCa)3 FeSiGe)5O12 bubble garnet is shown to have large effects on the growth-induced anisotropy (GIA). The presently accepted film composition intended for 6-or 8-micron-period bubble memory devices demands partial substitution of Y by Gd and Ho. However, comparing films grown under the same growth conditions, it is observed that YGdHoBilG films posess less (GIA) than their Gd, Ho-free counterparts. Thus, to satisfy (GIA) requirements, the supercooling during growth must be increased by 20 K to 80 K with undesirable effects on defect densities. A new film composition containing Sm, Tb, and Gd has been formulated to satisfy all known material property specifications for 6- or 8-micron-period memory devices. It can be grown with only 45-50 K supercooling.

Luther, L. C.↗
DOE OSTI2019

Shape memory embolectomy devices and systems

An embolectomy device comprised of an expansion unit and a support unit is disclosed. The expansion unit can be actuated in response to one or more external stimuli, and the support unit, located proximately to the expansion unit, provides a force to hold the expansion unit in place and to further induce the expansion unit's radial expansion. The radial expansion of the expansion unit causes the expansion unit to physically contact a blood clot, enabling the blood clot to be removed. In some embodiments, the expansion unit can be fabricated from a shape memory polymer foam. In some embodiments the support unit can be fabricated from any elastic material including, without limitation, shape memory alloys.

Szafron, Jason↗
DOE OSTI2022

Shape memory embolectomy devices and systems

An embolectomy device comprised of an expansion unit and a support unit is disclosed. The expansion unit can be actuated in response to one or more external stimuli, and the support unit, located proximately to the expansion unit, provides a force to hold the expansion unit in place and to further induce the expansion unit's radial expansion. The radial expansion of the expansion unit causes the expansion unit to physically contact a blood clot, enabling the blood clot to be removed. In some embodiments, the expansion unit can be fabricated from a shape memory polymer foam. In some embodiments the support unit can be fabricated from any elastic material including, without limitation, shape memory alloys.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Tailoring Spin Textures in Complex Oxide Micromagnets

Engineered topological spin textures with submicron dimensions in magnetic materials have emerged in recent years as the building blocks for various spin-based memory devices. Examples of these magnetic configurations include magnetic skyrmions, vortices, and domain walls. Here in this paper, we show the ability to control and characterize the evolution of spin textures in complex oxide micromagnets as a function of temperature through the delicate balance of fundamental materials parameters, micromagnet geometries, and epitaxial strain. These results demonstrate that in order to fully describe the observed spin textures, it is necessary to account for the spatial variation of the magnetic parameters within the micromagnet. This study provides the framework to accurately characterize such structures, leading to efficient design of spin-based memory devices based on complex oxide thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Apparatus and methods for memory using in-plane polarization

A memory device includes a semiconductor layer with an in-plane polarization component switchable between a first direction and a second direction. A writing electrode is employed to apply a writing voltage to the semiconductor layer to change the in-plane polarization component between the first direction and the second direction. A reading electrode is employed to apply a reading voltage to the semiconductor layer to measure a tunneling current substantially perpendicular to the polarization direction of the in-plane polarization component. The directions of the reading voltage and the writing voltage are substantially perpendicular to each other. Therefore, the reading process is non-destructive. Thin films (e.g., one unit cell thick) of ferroelectric material can be used in the memory device to increase the miniaturization of the device.

42 ENGINEERING↗
DOE OSTI2018

Intrinsic Two-Dimensional Ferroelectricity with Dipole Locking

Out-of-plane ferroelectricity with a high transition temperature in ultrathin films is important for the exploration of new domain physics and scaling down of memory devices. However, depolarizing electrostatic fields and interfacial chemical bonds can destroy this long-range polar order at two-dimensional (2D) limit. In this paper we report the experimental discovery of the locking between out-of-plane dipoles and in-plane lattice asymmetry in atomically thin In 2 Se 3 crystals, a new stabilization mechanism leading to our observation of intrinsic 2D out-of-plane ferroelectricity. Through second harmonic generation spectroscopy and piezoresponse force microscopy, we found switching of out-of-plane electric polarization requires a flip of nonlinear optical polarization that corresponds to the inversion of in-plane lattice orientation. The polar order shows a very high transition temperature (~700Κ) without the assistance of extrinsic screening. This finding of intrinsic 2D ferroelectricity resulting from dipole locking opens up possibilities to explore 2D multiferroic physics and develop ultrahigh density memory devices.

2-dimensional systems↗
DOE OSTI2025

Field-free switching of perpendicular magnetization in a ferrimagnetic insulator with spin reorientation transition

Writing magnetic bits through spin-orbit torque (SOT) switching is promising for fast and efficient magnetic random-access memory devices. While SOT switching of out-of-plane (OOP) magnetized states requires lateral symmetry breaking, in-plane (IP) magnetized states suffer from low storage density. Here, we demonstrate a field-free switching scheme using a 5-nanometer europium iron garnet film grown with a (110) orientation that shows a spin reorientation transition from OOP to IP above room temperature. This scheme combines the benefits of high-density storage in the OOP states at room temperature and the efficient field-free SOT switching in the IP states at elevated temperatures. While conventional switching of OOP bits faces the dilemma that high OOP anisotropy is required to improve bit stability and low OOP anisotropy is required to lower switching current density, this scheme disentangles this interdependence, allowing for low switching currents to be possible without sacrificing the bit stability, offering opportunities for future memory devices.

Science & Technology - Other Topics↗
DOE OSTI2025

Magnetic Switching in Monolayer 2D Diluted Magnetic Semiconductors via Spin‐to‐Spin Conversion

Abstract The integration of 2D van der Waals (vdW) magnets with topological insulators or heavy metals holds great potential for realizing next‐generation spintronic memory devices. However, achieving high‐efficiency spin–orbit torque (SOT) switching of monolayer vdW magnets at room temperature poses a significant challenge, particularly without an external magnetic field. Here, it is shown field‐free, deterministic, and nonvolatile SOT switching of perpendicular magnetization in the monolayer, diluted magnetic semiconductor (DMS), Fe‐doped MoS 2 (Fe:MoS 2 ) at up to 380 K with a current density of ≈7 × 10 4 A cm −2 . The in situ doping of Fe into monolayer MoS 2 via chemical vapor deposition and the geometry‐induced strain in the crystal break the rotational switching symmetry in Fe:MoS 2 , promoting field‐free SOT switching by generating out‐of‐plane spins via spin‐to‐spin conversion. An apparent anomalous Hall effect (AHE) loop shift at a zero in‐plane magnetic field verifies the existence of z spins in Fe:MoS 2 , inducing an antidamping‐like torque that facilitates field‐free SOT switching. This field‐free SOT application using a 2D ferromagnetic monolayer provides a new pathway for developing highly power‐efficient spintronic memory devices.

Chen, Siwei [Department of Mechanical Engineering ↗
DOE OSTI2014

SSD-optimized workload placement with adaptive learning and classification in HPC environments

In recent years, non-volatile memory devices such as SSD drives have emerged as a viable storage solution due to their increasing capacity and decreasing cost. Due to the unique capability and capacity requirements in large scale HPC (High Performance Computing) storage environment, a hybrid configuration (SSD and HDD) may represent one of the most available and balanced solutions considering the cost and performance. Under this setting, effective data placement as well as movement with controlled overhead become a pressing challenge. In this paper, we propose an integrated object placement and movement framework and adaptive learning algorithms to address these issues. Specifically, we present a method that shuffle data objects across storage tiers to optimize the data access performance. The method also integrates an adaptive learning algorithm where realtime classification is employed to predict the popularity of data object accesses, so that they can be placed on, or migrate between SSD or HDD drives in the most efficient manner. We discuss preliminary results based on this approach using a simulator we developed to show that the proposed methods can dynamically adapt storage placements and access pattern as workloads evolve to achieve the best system level performance such as throughput.

Wan, Lipeng↗
NASA NTRS1998

Interaction between Convection and Heat Transfer in Crystal Growth

Crystals are integral components in some of our most sophisticated and rapidly developing industries. Single crystals are solids with the most uniform structures that can be obtained on an atomic scale. Because of their structural uniformity, crystals can transmit acoustic and electromagnetic waves and charged particles with essentially no scattering or interferences. This transparency, which can be selectively modified by controlled additions of impurities known as dopants, is the foundation of modern electronic industry. It has brought about widespread application of crystals in transistors, lasers, microwave devices, infrared detectors, magnetic memory devices, and many other magnets and electro-optic components. The performance of a crystal depends strongly on its compositional homogeneity. For instance, in modern microcircuitry, compositional variations of a few percent (down to a submicron length scale) can seriously jeopardize predicted yields. Since crystals are grown by carefully controlled phase transformations, the compositional adjustment in the solid is often made during growth from the nutrient. Hence, a detailed understanding of mass transfer in the nutrient is essential. Moreover, since mass transfer is often the slowest process during growth, it is usually the rate limiting mechanism. Crystal growth processes are usually classified according to the nature of the parent phase. Nevertheless, whether the growth occurs by solidification from a melt (melt growth), nucleation from a solution (solution growth), condensation from a vapor (physical vapor transport) or chemical reaction of gases (chemical vapor deposition), the parent phase is a fluid. As is with most non-equilibrium processes involving fluids, liquid or vapor, fluid motion plays an important role, affecting both the concentration and temperature gradients at the soli-liquid interface.

Source record↗
DOE OSTI2012

{100}<100> or 45.degree.-rotated {100}<100>, semiconductor-based, large-area, flexible, electronic devices

Novel articles and methods to fabricate the same resulting in flexible, {100}<100> or 45.degree.-rotated {100}<100> oriented, semiconductor-based, electronic devices are disclosed. Potential applications of resulting articles are in areas of photovoltaic devices, flat-panel displays, thermophotovoltaic devices, ferroelectric devices, light emitting diode devices, computer hard disc drive devices, magnetoresistance based devices, photoluminescence based devices, non-volatile memory devices, dielectric devices, thermoelectric devices and quantum dot laser devices.

42 ENGINEERING↗