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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Filament-Free Bulk Resistive Memory Enables Deterministic Analogue Switching

Digital computing is nearing its physical limits as computing needs and energy consumption rapidly increase. Analogue-memory-based neuromorphic computing can be orders of magnitude more energy efficient at data-intensive tasks like deep neural networks, but has been limited by the inaccurate and unpredictable switching of analogue resistive memory. Filamentary resistive random access memory (RRAM) suffers from stochastic switching due to the random kinetic motion of discrete defects in the nanometer-sized filament. Here, this stochasticity is overcome by incorporating a solid electrolyte interlayer, in this case, yttria-stabilized zirconia (YSZ), toward eliminating filaments. Filament-free, bulk-RRAM cells instead store analogue states using the bulk point defect concentration, yielding predictable switching because the statistical ensemble behavior of oxygen vacancy defects is deterministic even when individual defects are stochastic. Both experiments and modeling show bulk-RRAM devices using TiO2-X switching layers and YSZ electrolytes yield deterministic and linear analogue switching for efficient inference and training. Bulk-RRAM solves many outstanding issues with memristor unpredictability that have inhibited commercialization, and can, therefore, enable unprecedented new applications for energy-efficient neuromorphic computing. Beyond RRAM, this work shows how harnessing bulk point defects in ionic materials can be used to engineer deterministic nanoelectronic materials and devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deterministic Ferroelastic Domain Switching Using Ferroelectric Bilayers

Composition gradients, or dissimilar ferroelectric bilayers, demonstrate colossal electromechanical figures of merit attributed to the motion of ferroelastic domain walls. Yet, mechanistic understanding of polarization switching pathways that drive ferroelastic switching in these systems remains elusive. Here, the crucial roles of strain and electrostatic boundary conditions in ferroelectric bilayer systems are revealed, which underpin their ferroelastic switching dynamics. Using in situ electrical biasing in the transmission electron microscope (TEM), the motion of ferroelastic domain walls is investigated in a tetragonal (T) Pb(Zr,Ti)O 3 (PZT)/rhombohedral (R) PZT epitaxial bilayer system. Atomic resolution electron microscopy, in tandem with phase field simulations, indicates that ferroelastic switching is triggered by predominant nucleation at the triple domain junctions located at the interface between the T/R layers. Furthermore, this interfacial nucleation leads to systematic reversable reorientation of ferroelastic domain walls. Finally, deterministic ferroelastic domain switching, driven by the interfacial strain and electrostatic boundary conditions in the ferroelectric bilayer, provides a viable pathway toward novel design of miniaturized energy-efficient electromechanical devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Antiphase-Boundary-Engineered Domain Switching in a (110)-Oriented BiFeO 3 Film

A ferroelectric domain wall memory device exploits the presence (or absence) of domain walls as the basis for information storage. Although structural defects strongly influence ferroelectric domain wall nucleation and growth, this correlation is far from being fully understood. For example, a single defect can play opposing roles: it can act as a nucleation site to initiate domain switching or, conversely, serve as a pinning center inhibiting domain wall motion. This is particularly the case for antiphase boundaries (APBs), whose influence on switching remains relatively unexplored despite being ubiquitous in oxide perovskite ferroelectrics. Here, we use aberration-corrected scanning transmission microscopy and in situ transmission electron microscopy under an applied bias to extensively characterize the influence of an APB on the switching behavior in a (110)-oriented BiFeO 3 thin film. We demonstrate that deterministic nucleation occurs in the proximity of a vertically oriented APB, following which domain growth occurs laterally in a symmetric fashion. Atomic-scale structural analysis reveals that the shear operation vector for the APB is 1/2[110]; this half-unit-cell shift extends over a few nanometers, implying that the APB plane is inclined toward the imaging direction. The symmetric switching observation is attributed to local inhomogeneous lattice strain and a reduction of polarization caused by the APB. These results demonstrate that an extended structural defect can be used as an active switching element rather than a stumbling block in reprogrammable domain-wall-based devices. Ultimately, this will expand the capabilities of ferroelectric thin films for future electronic devices based on ferroelectric domain walls.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Chemical state evolution in ferroelectric films during tip-induced polarization and electroresistive switching

Domain formation and ferroelectric switching is fundamentally inseparable from polarization screening, which on free surfaces can be realized via band bending and ionic adsorption. In the latter case, polarization switching is intrinsically coupled to the surface electrochemical phenomena, and the electrochemical stage can control kinetics and induce long-range interactions. However, despite extensive evidence towards the critical role of surface electrochemistry, little is known about the nature of the associated processes. Here we combine SPM tip induce polarization switching and secondary ion mass spectrometry to explore the evolution of chemical state of ferroelectric during switching. Surprisingly, we find that even pristine surfaces contain ions (e.g. Cl - ) that are not anticipated based on chemistry of the system and processing. In the ferroelectric switching regime, we find surprising changes in surface chemistry, including redistribution of base cations. Finally, at higher voltages in the electroforming regime significant surface deformation was observed and associated with a strong ion intermixing.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comparison of Kill Switch Toxins in Plant-Beneficial Pseudomonas fluorescens Reveals Drivers of Lethality, Stability, and Escape

Kill switches provide a biocontainment strategy in which unwanted growth of an engineered microorganism is prevented by expression of a toxin gene. A major challenge in kill switch engineering is balancing evolutionary stability with robust cell killing activity in application relevant host strains. Understanding host-specific containment dynamics and modes of failure helps to develop potent yet stable kill switches. To guide the design of robust kill switches in the agriculturally relevant strain Pseudomonas fluorescens SBW25, we present a comparison of lethality, stability, and genetic escape of eight different toxic effectors in the presence of their cognate inactivators (i.e., toxin–antitoxin modules, polymorphic exotoxin–immunity systems, restriction endonuclease–methyltransferase pair). We find that cell killing capacity and evolutionary stability are inversely correlated and dependent on the level of protection provided by the inactivator gene. Decreasing the proteolytic stability of the inactivator protein can increase cell killing capacity, but at the cost of long-term circuit stability. By comparing toxins within the same genetic context, we determine that modes of genetic escape increase with circuit complexity and are driven by toxin activity, the protective capacity of the inactivator, and the presence of mutation-prone sequences within the circuit. Here, the results of our study reveal that circuit complexity, toxin choice, inactivator stability, and DNA sequence design are powerful drivers of kill switch stability and valuable targets for optimization of biocontainment systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Discrete-time systems with random switches: From systems stability to networks synchronization

In this article, we develop some approaches, which enable us to more accurately and analytically identify the essential patterns that guarantee the almost sure stability of discrete-time systems with random switches. We allow for the case that the elements in the switching connection matrix even obey some unbounded and continuous-valued distributions. In addition to the almost sure stability, we further investigate the almost sure synchronization in complex dynamical networks consisting of randomly connected nodes. Numerical examples illustrate that a chaotic dynamics in the synchronization manifold is preserved when statistical parameters enter some almost sure synchronization region established by the developed approach. Moreover, some delicate configurations are considered on probability space for ensuring synchronization in networks whose nodes are described by nonlinear maps. Both theoretical and numerical results on synchronization are presented by setting only a few random connections in each switch duration. More interestingly, we analytically find it possible to achieve almost sure synchronization in the randomly switching complex networks even with very large population sizes, which cannot be easily realized in non-switching but deterministically connected networks.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Temperature induced complementary switching in titanium oxide resistive random access memory

On the way towards high memory density and computer performance, a considerable development in energy efficiency represents the foremost aspiration in future information technology. Complementary resistive switch consists of two antiserial resistive switching memory (RRAM) elements and allows for the construction of large passive crossbar arrays by solving the sneak path problem in combination with a drastic reduction of the power consumption. Here we present a titanium oxide based complementary RRAM (CRRAM) device with Pt top and TiN bottom electrode. A subsequent post metal annealing at 400°C induces CRRAM. Forming voltage of 4.3 V is required for this device to initiate switching process. The same device also exhibiting bipolar switching at lower compliance current, Ic <50 μA. The CRRAM device have high reliabilities. Formation of intermediate titanium oxi-nitride layer is confirmed from the cross-sectional HRTEM analysis. The origin of complementary switching mechanism have been discussed with AES, HRTEM analysis and schematic diagram. This paper provides valuable data along with analysis on the origin of CRRAM for the application in nanoscale devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Giant resistance switch in twisted transition metal dichalcogenide tunnel junctions

Resistance switching in multilayer structures are typically based on materials possessing ferroic orders. Here, in this work, we predict an extremely large resistance switching based on the relative spin–orbit splitting in twisted transition metal dichalcogenide (TMD) monolayers tunnel junctions. Because of the valence band spin splitting which depends on the valley index in the Brillouin zone, the perpendicular electronic transport through the junction depends on the relative reciprocal space overlap of the spin-dependent Fermi surfaces of both layers, which can be tuned by twisting one layer. Our quantum transport calculations reveal a switching resistance larger than 10 6 % when the relative alignment of TMDs goes from 0° to 60° and when the angle is kept fixed at 60° and the Fermi level is varied. By creating vacancies, we evaluate how inter-valley scattering affects the efficiency and find that the resistance switching remains large (10 4 %) for typical values of vacancy concentration. Not only should this resistance switching be observed at room temperature due to the large spin splitting, but our results also show how twist angle engineering and control of van der Waals heterostructures could be used for next-generation memory and electronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Cavity-assisted magnetization switching in a quantum spin-phonon chain

Néel order switching in antiferromagnets has typically required intense optical driving, leading to substantial heating and limited efficiency. By placing antiferromagnets inside a terahertz-driven optical cavity, we propose a multi-particle mechanism for Néel order switching that benefits from reduced heating. Our analysis reveals that phonons are indispensable to this mechanism. A driven cavity mode couples to a spin-phonon chain, with all excitations dissipating energy through external baths. Mean-field analysis shows that cavity photons induce sublattice spin-density imbalance—an intrinsic symmetry-breaking effect absent without the cavity. Contrary to known (1–10 V/nm) laser fields required to switch the Néel order, our mechanism enables switching at remarkably low laser fields (1–5 V/μm), selectively targeting low-energy and perpendicular magnon modes. By virtue of the suppressed heating, the switching remains highly tunable through laser fluence, damping, and photon loss, establishing a low-dissipation route toward cavity-assisted opto-spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Direct imaging of electrical switching of antiferromagnetic Néel order in α-Fe 2 O 3 epitaxial films

In this work, we report the direct observation of switching of the Néel vector of antiferromagnetic (AFM) domains in response to electrical pulses in micron-scale Pt/α-Fe 2 O 3 Hall bars using photoemission electron microscopy. Current pulses lead to reversible and repeatable switching with the current direction determining the final state, consistent with Hall effect experiments that probe only the spatially averaged response. Current pulses also produce irreversible changes in domain structure, in and even outside the current path. In both cases only a fraction of the domains switch in response to pulses. Furthermore, the analysis of images taken with different x-ray polarizations shows that the AFM Néel order has an out-of-plane component in equilibrium that is important to consider in analyzing the switching data. These results show that—in addition to effects associated with spin-orbit torques from the Pt layer, which can produce reversible switching—changes in AFM order can be induced by purely thermal effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Analysis and Experimental Evaluation of Middle-Point Inductance's Effect on Switching Transients for Multiple-Chip Power Module Package

Middle-point inductance L middle can be introduced in multiple-chip power module package designs. In this paper, the effect of middle-point inductance on switching transients is analyzed first using a frequency-domain analysis. Then a dedicated multiple-chip power module is fabricated with the capability of varying L middle , and extensive switching tests are conducted to evaluate the middle-point inductance's impact. Experiment result shows that the active MOSFET's turn-on loss decreases at higher values of L middle , while its turn-off loss increases. Detailed analysis of this loss variation is presented. In addition to the switching loss variation, it is also observed that different peak voltage stresses are imposed on the active switch and antiparallel diode during the switching transients. Specifically, in the case of lower MOSFET's turn-off, the maximum voltage of the lower MOSFET increases as L middle goes up; however, the peak voltage of the antiparallel diode decreases significantly. Furthermore, the induced voltage spikes during upper MOSFET turn-on process is also evaluated, and an opposite trend is observed experimentally. Analysis of the voltage overshoot variation is discussed. Based on the experimental evaluation and analysis, a multiple-chip power module package design guideline is summarized considering the middle-point inductance's effect.

42 ENGINEERING↗
DOE OSTI2016

A high-current rail-type gas switch with preionization by an additional corona discharge

The characteristics of a high-current rail-type gas switch with preionization of the gas (air) in a spark gap by an additional corona discharge are investigated. The experiments were performed in a voltage range of 10–45 kV using a two-electrode switch consisting of two cylindrical electrodes with a diameter of 22 mm and a length of 100 mm and a set of laterally located corona-discharge needles. The requirements for the position and size of the needles are defined for which a corona discharge is ignited before a breakdown of the main gap and does not change to a sparking form, and the entire length of the rail electrodes is efficiently used. The fulfillment of these requirements ensures stable operation of the switch with a small variation of the pulse breakdown voltage, which is not more than 1% for a fixed voltage-pulse rise time in the range from 150 ns to 3.5 μs. A short delay time of the switch breakdown makes it possible to control the two-electrode switch by an overvoltage pulse of nanosecond duration.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

High-Power Nano- and Picosecond Optoelectronic Switches Based on High-Voltage Silicon Structures with p–n Junctions. III. Self-Heating Effects

The self-heating effects of optoelectronic switches based on vertical high-voltage structures with p–n junctions (Vertical Photoactivated Semiconductor Switches, VPSS) operating in the high-frequency mode are theoretically studied for the first time. It is shown that the strong temperature dependence of the control-radiation absorbance κ(T) is a major factor controlling the maximum switching frequency f{sub max} and the corresponding maximum crystal temperature T{sub max}, as well as the temperature T and current density j distributions over the device area. Two-dimensional analysis of the simplest electrothermal model of a VPSS embedded into a double coaxial forming line shows that an increase in the switching frequency f leads to current displacement to the device periphery where the temperature is minimum. However, the T and j distributions over the device area remain stable at f < f{sub max} and T < T{sub max}. Certainly, f{sub max} and T{sub max} depend on the control-radiation pulse energy, pulse switching power, and heat-removal conditions. For the VPSS based on indirect-gap semiconductors (Si, SiC), they vary within 20–120 kHz and 120–160°C which is quite sufficient for practical applications. However, VPSSs based on direct-gap semiconductors (GaAs, InP) are in fact inapplicable to operation in high-frequency modes due to the fact that the dependence κ(T) is too sharp.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

A numerical approach for detecting switch-like bistability in mass action chemical reaction networks with conservation laws

Theoretical analysis of signaling pathways can provide a substantial amount of insight into their function. One particular area of research considers signaling pathways capable of assuming two or more stable states given the same amount of signaling ligand. This phenomenon of bistability can give rise to switch-like behavior, a mechanism that governs cellular decision making. Investigation of whether or not a signaling pathway can confer bistability and switch-like behavior, without knowledge of specific kinetic rate constant values, is a mathematically challenging problem. Recently a technique based on optimization has been introduced, which is capable of finding example parameter values that confer switch-like behavior for a given pathway. Although this approach has made it possible to analyze moderately sized pathways, it is limited to reaction networks that presume a uniterminal structure. It is this limited structure we address by developing a general technique that applies to any mass action reaction network with conservation laws. In this paper we developed a generalized method for detecting switch-like bistable behavior in any mass action reaction network with conservation laws. The method involves (1) construction of a constrained optimization problem using the determinant of the Jacobian of the underlying rate equations, (2) minimization of the objective function to search for conditions resulting in a zero eigenvalue, (3) computation of a confidence level that describes if the global minimum has been found and (4) evaluation of optimization values, using either numerical continuation or directly simulating the ODE system, to verify that a bistability region exists. The generalized method has been tested on three motifs known to be capable of bistability. We have developed a variation of an optimization-based method for the discovery of bistability, which is not limited to uniterminal chemical reaction networks. Successful completion of the method provides an S-shaped bifurcation diagram, which indicates that the network acts as a bistable switch for the given optimization parameters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2009

Electrostatic Switching in Vertically Oriented Nanotubes for Nonvolatile Memory Applications

We have demonstrated electrostatic switching in vertically oriented nanotubes or nanofibers, where a nanoprobe was used as the actuating electrode inside an SEM. When the nanoprobe was manipulated to be in close proximity to a single tube, switching voltages between 10 V - 40 V were observed, depending on the geometrical parameters. The turn-on transitions appeared to be much sharper than the turn-off transitions which were limited by the tube-to-probe contact resistances. In many cases, stiction forces at these dimensions were dominant, since the tube appeared stuck to the probe even after the voltage returned to 0 V, suggesting that such structures are promising for nonvolatile memory applications. The stiction effects, to some extent, can be adjusted by engineering the switch geometry appropriately. Nanoscale mechanical measurements were also conducted on the tubes using a custom-built anoindentor inside an SEM, from which preliminary material parameters, such as the elastic modulus, were extracted. The mechanical measurements also revealed that the tubes appear to be well adhered to the substrate. The material parameters gathered from the mechanical measurements were then used in developing an electrostatic model of the switch using a commercially available finite-element simulator. The calculated pull-in voltages appeared to be in agreement to the experimentally obtained switching voltages to first order.

plasma-enhanced chemical vapor deposition (PECVD).↗
NASA NTRS2008

Carbon Nanotube Switches for Communication and Memory Applications

Lateral CNT Switches: a) dc CNT switches were demonstrated to operate at low voltages, low powers and high speeds. b) RF simulations of switch in series configuration with metallized tube yielded good RF performance 1) Isolation simulated to be approx. 20 dB at 100 GHz. 2) Insertion loss simulated to be < 0.5 dB at 100 GHz. Vertical CNT Switches: a) Thermal CVD was used to mechanically constrain tubes in nanopockets; tubes not self-supporting. b) Demonstrated growth of vertically aligned arrays and single-few MWNTs using dc PECVD with Ni catalyst using optical lithography.

memory devices↗
DOE OSTI2023

Nonvolatile Magnetoelectric Switching of Magnetic Tunnel Junctions with Dipole Interaction

The magnetoelectric effect is technologically appealing because of its ability to manipulate magnetism using an electric field rather than magnetic field or current, thus providing a promising solution for the development of energy-efficient spintronics. Although 180° magnetization switching is vital to spintronic devices, the achievement of 180° magnetization switching via magnetoelectric coupling is still a fundamental challenge. Here, in this work, voltage-driven full resistance switching of a magnetic tunnel junction (MTJ) with dipole interaction on a ferroelectric substrate through switchable parallel/antiparallel magnetization alignment is demonstrated. Parallel magnetization alignment along the y direction is obtained under a bias magnetic field. By rotating the magnetic easy axis via strain-mediated magnetoelectric coupling, the parallel magnetizations in the MTJ reorient to the x axis with opposite paths because of dipole interaction, thus resulting in antiparallel alignment. Moreover, this voltage switching of MTJs is nonvolatile owing to variations in dipole interaction and can be well understood via phase field simulations. The results provide an avenue to realize electrical switching of MTJs and are significant for exploring energy-efficient spintronic devices.

36 MATERIALS SCIENCE↗
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 ↗