Nonvolatile Data Storage Research Articles

All Roads Lead to Rome: Tuning the Luminescence of a Breathing Catenated Zr-MOF by Programmable Multiplexing Pathways

A zirconium-based metal–organic framework (Zr-MOF) with a 2-fold catenated breathing structure is designed, whose framework contracts in a similarly consecutive manner responsive to solvent (S), temperature (T), or pressure (P). As a result, photoluminescence color tuning (PLCT) can be achieved progressively from blue to yellow, via S, T, or P pathways, leading to multiple PL states with memory nature. Based on this, a 3D PLCT coordinate system is established. Along each stimulation pathway, the starting, ending, and multiple intermediate PLCT states can be recognized and plotted on the S, T, and P axes of the coordinate system. Furthermore, multiplexing node-transfer pathways are programmed among the axes, in which two or three kinds of outer stimuli (S/T/P) are implemented successively and alternatively, leading to various stages of PL states. This multiplexing approach provides a new strategy to control and utilize the multiresponsiveness of PL-MOFs for intriguing applications such as composite nonvolatile data storage and so on.

A Nonvolatile Phase‐Change Metamaterial Color Display

AbstractChalcogenide phase‐change materials, which exhibit a marked difference in their electrical and optical properties when in their amorphous and crystalline phases and can be switched between these phases quickly and repeatedly, are traditionally exploited to deliver nonvolatile data storage in the form of rewritable optical disks and electrical phase‐change memories. However, exciting new potential applications are now emerging in areas such as integrated phase‐change photonics, phase‐change optical metamaterials/metasurfaces, and optoelectronic displays. Here, ideas from these last two fields are fused together to deliver a novel concept, namely a switchable phase‐change metamaterial/metasurface resonant absorber having nonvolatile color generating capabilities. With the phase‐change layer, here GeTe, in the crystalline phase, the resonant absorber can be tuned to selectively absorb the red, green, and blue spectral bands of the visible spectrum, so generating vivid cyan, magenta, and yellow pixels. When the phase‐change layer is switched into the amorphous phase, the resonant absorption is suppressed and a flat, pseudowhite reflectance results. Thus, a route to the potential development is opened‐up of nonvolatile, phase‐change metamaterial color displays and color electronic signage.

Core-shell copper nanowire-TiO2 nanotube arrays with excellent bipolar resistive switching properties

Electrochemical nanomaterial-based resistive switching devices (memristors) have recently attracted significant research interest because of their low cost and potential applications in nonvolatile data storage and artificial neural networks. In this paper, we report an electrochemical method to produce a novel memristor based on copper nanowire-titanium dioxide nanotube arrays (TNTAs), a core-shell composite material. TNTAs are fabricated using a cheap and effective electrochemical anodization method, and high-density copper nanowires are synthesized via excess-electrodeposition with a novel peeling-off strategy. This novel memristor shows both analogue and digital resistive switching properties by controlling the electroforming process. The Roff/Ron ratio of the digital memristor remains greater than 40 during 1000 consecutive I–V sweeps. The device shows good endurance over 104 pulse cycles, with an Roff/Ron ratio greater than 20. Furthermore, the data retention time can be maintained at least for 104 s. The outstanding digital resistive switching performance can be attributed to the numerous parallel copper nanowire nanoelectrodes inside the film.

Multiferroic properties of Gd/Er doped chromium ferrite nano sized particles synthesized by citrate auto combustion method

The non-stoichiometric Gd/Er doped Chromium nano ferrite with uniform and tunable size has been successfully synthesized by citrate auto combustion method. The prepared samples exhibit a combination of nonstoichiometry and non electroneutrality. The neutrality in the investigated samples is well maintained via the reduction of oxygen or removal of Cr ions. The ferromagnetic as well as the ferroelectric hysteresis loops of the investigated samples were studied. The obtained data shows that the antiferromagnetic nature in CrFe2O4 (CrFeO3) is turned into weak ferromagnetism in rare earth doped chromium. The substitution of rare earth ions for Fe can dramatically improve the saturation magnetization and remnant magnetization. The band gap energy was calculated from near infrared (NIR) and visible (VIS) reflectance spectra using the Kubelka-Munk function. Special attention should be given to chromium ferrite nanoparticles which are suitable candidates to be used in many applications like non-volatile data storage and camera flashes due to their ferroelectrics properties.

Dependence of structural cross-linking, system energy and transition temperature on coordination number for Sm doped GST

Abstract Ge2Sb2Te5 is one of the prominent phase change memory material for non-volatile data storage due to high crystallization temperature and fast crystallization speed. The physical correlations have been employed to narrate the structural alteration of Ge2Sb2Te5 on Sm incorporation. The calculation of structural change has been performed by calculating the change in net constraints (Ncon) with mean coordination (Z) on Sm addition. There is an increase in fraction of zero frequency modes (Mf) and cross-linking density (DCL) on Sm incorporation. The structural cross-linking shows a three dimensional network formation. There is an enhancement in density and compactness on Sm addition. The degree of covalency (>93%) shows a decrease in ordering and leading to an increase in glass formation tendency. The calculated values of band gap show an increase on Sm addition which is in good agreement with increase in cohesive energy calculated using chemical bond approach (CBA). Using CBA, the glass transition temperature has been estimated and is correlated with the increase in cross-linking in the system.

Spin tunnel field-effect transistors based on two-dimensional van der Waals heterostructures

A transistor based on spin rather than charge—a spin transistor—could potentially offer non-volatile data storage and improved performance compared with traditional transistors. Many approaches have been explored to realize spin transistors, but their development remains a considerable challenge. The recent discovery of two-dimensional magnetic insulators such as chromium triiodide (CrI3), which offer electrically switchable magnetic order and an effective spin filtering effect, can provide new operating principles for spin transistors. Here, we report spin tunnel field-effect transistors (TFETs) based on dual-gated graphene/CrI3/graphene tunnel junctions. The devices exhibit an ambipolar behaviour and tunnel conductance that is dependent on the magnetic order in the CrI3 tunnel barrier. The gate voltage switches the tunnel barrier between interlayer antiferromagnetic and ferromagnetic states under a constant magnetic bias near the spin-flip transition, thus effectively and reversibly altering the device between a low and a high conductance state, with large hysteresis. By electrically controlling the magnetization configurations instead of the spin current, our spin TFETs achieve a high–low conductance ratio approaching 400%, suggesting they could be of value in the development of non-volatile memory applications. A tunnel field-effect transistor with spin-dependent outputs that are voltage controllable and reversible can be created using a dual-gated graphene/CrI3/graphene tunnel junction.

Selective control of magnetism in FeAl/PIN-PMN-PT using an electric field

Mediating nonvolatile magnetism by purely electrical methods is a crucial challenge for the development of high-density and low energy consumption information storage. Research into most material systems, including ferromagnetic /ferroelectric heterostructures and, especially, magnetostriction/lead magnesium niobate-lead titanate (PMN-PT), has focused mainly on the nonvolatile strain-mediated converse magnetoelectric (ME) effect. The recent discovery of a type of FeAl/lead indium niobate (PIN)-PMN-PT heterostructure has provided an approach for electrical control of magnetism at room temperature. We demonstrate selective control of nonvolatile magnetism in (001)- and (111)-oriented FeAl/PIN-PMN-PT. In order to illustrate the behavior of electric field control of magnetism in (111)-oriented PIN-PMN-PT, a converse ME coupling mechanism is presented via polarization switching models. This mechanism indicates that the magnetization process is related to both the direction of polarization switching and the strain-mediated effect. By controlling the piezoresponse force microscopy (PFM) scan direction and analyzing the color contrast of the PFM images, we confirm the validity of the proposed models of polarization switching and demonstrate the validity of the mechanism. The results of this study may offer a method for the selective control of magnetism in nonvolatile multilevel data storage.

Shear strain-induced anisotropic domain evolution in mixed-phase BiFeO3 epitaxial films

Understanding and controlling the domain evolution under external stimuli in multiferroic thin films is critical to realizing nanoelectronic devices, including for non-volatile memory, data storage, sensors, and optoelectronics. In this article, we studied the shear-strain effect on the domain evolution with temperature in highly strained BiFeO3 thin films on rhombohedral LaAlO3 substrates using a high-resolution synchrotron X-ray diffraction three dimensional-reciprocal space mapping (3D-RSM) technique. The results revealed significant biaxial, anisotropic, evolution behaviors of the mixed-phase (MC + R′/T′ phases) BiFeO3 ferroelectric domains along the in-plane [100] and [010] axes. These biaxial, anisotropic, evolution behaviors were attributed to the shear-strain-modulated transition pathways of the mixed-phase ferroelectric domains. This viewpoint was further verified in the BiFeO3/LaSrAlO4 (001) system in which no anisotropic evolution behaviors of the mixed-phase domains were found. This work sheds light on the quantitative analysis of domain evolution in multi-domain systems and demonstrates that the shear-strain effect could act as an effective tool to manipulate the domain behavior and control novel functionalities of ferroelectric thin films.

Tubular 3D Resistive Random Access Memory Based on Rolled-Up h-BN Tube.

Due to their advantages compared with planar structures, rolled-up tubes have been applied in many fields, such as field-effect transistors, compact capacitors, inductors, and integrative sensors. On the other hand, because of its perfect insulating nature, ultrahigh mechanical strength and atomic thickness property, 2D hexagonal boron nitride (h-BN) is a very suitable material for rolled-up memory applications. In this work, a tubular 3D resistive random access memory (RRAM) device based on rolled-up h-BN tube is realized, which is achieved by self-rolled-up technology. The tubular RRAM device exhibits bipolar resistive switching behavior, nonvolatile data storage ability, and satisfactorily low programming current compared with other 2D material-based RRAM devices. Moreover, by releasing from the substrate, the footprint area of the tubular device is reduced by six times. This tubular RRAM device has great potential for increasing the data storage density, lowering the power consumption, and may be applied in the fields of rolled-up systems and sensing-storage integration.

Electrical properties and structural transition of Ge2Sb2Te5 adjusted by rare-earth element Gd for nonvolatile phase-change memory

Phase change memory has been considered as the next generation in non-volatile electronic data storage. The property modulation of such materials by the doping of rare-earth elements has drawn a lot of attention, which motivates us to search for the optimal dopants and reveal the underlying mechanisms. Here, we investigate the role of Gd as a dopant in Ge2Sb2Te5, which exhibits higher crystalline resistance and better thermal stability and antioxidant capacity than the undoped counterpart. Moreover, Gd dopants suppress both the processes of phase transition and grain growth. The crystalline structure remains unchanged with Gd dopants and vacancies are randomly distributed. Furthermore, the bonding mechanism was theoretically investigated. In the amorphous state, Gd atoms modify the local structures around Ge, Sb, and Te atoms. The large coordination number of Gd and the “Gd–Te distorted pentagonal bipyramidal-like” structure can be attributed to the good thermal stability. These microscopic findings figure out some of the key issues about the bonding mechanism, electrical properties, and crystallization behaviors of Gd doped phase change memory materials, which could be useful for storage devices.

Discrete Hall resistivity contribution from Néel skyrmions in multilayer nanodiscs.

Magnetic skyrmions are knot-like quasiparticles. They are candidates for non-volatile data storage in which information is moved between fixed read and write terminals. The read-out operation of skyrmion-based spintronic devices will rely on the electrical detection of a single magnetic skyrmion within a nanostructure. Here we present Pt/Co/Ir nanodiscs that support skyrmions at room temperature. We measured the Hall resistivity and simultaneously imaged the spin texture using magnetic scanning transmission X-ray microscopy. The Hall resistivity is correlated to both the presence and size of the skyrmion. The size-dependent part matches the expected anomalous Hall signal when averaging the magnetization over the entire disc. We observed a resistivity contribution that only depends on the number and sign of skyrmion-like objects present in the disc. Each skyrmion gives rise to 22 ± 2 nΩ cm irrespective of its size. This contribution needs to be considered in all-electrical detection schemes applied to skyrmion-based devices. Not only the area of Néel skyrmions but also their number and sign contribute to their Hall resistivity.

Proposing a Solution for Single-Event Upset in 1T1R RRAM Memory Arrays

Resistive random access memory (RRAM) is a promising emerging technology to provide nonvolatile and scalable data storage in advanced technologies. As a noncharge-based device, the intrinsic RRAM device is immune to single-event effects. However, single-event upset (SEU) due to the MOSFET in the one-transistor-one-RRAM (1T1R) array can be observed. A novel methodology, which can be easily integrated to the other memory system components, is proposed in this paper to detect and correct SEU in 1T1R RRAM memory array. Using the HfO x 1T1R RRAM array as an example, our simulation results show that, for an 8-Gb memory array, the proposed technique can detect and fix the soft errors induced by the heavy ion strikes with 0.66% increase in the chip area. Also, the suggested methodology minimally increases the energy consumption of the read and write operations by 0.2% and 0.1%, respectively.

A Centimeter-Scale Inorganic Nanoparticle Superlattice Monolayer with Non-Close-Packing and its High Performance in Memory Devices.

Due to the near-field coupling effect, non-close-packed nanoparticle (NP) assemblies with tunable interparticle distance (d) attract great attention and show huge potential applications in various functional devices, e.g., organic nano-floating-gate memory (NFGM) devices. Unfortunately, the fabrication of device-scale non-close-packed 2D NPs material still remains a challenge, limiting its practical applications. Here, a facile yet robust "rapid liquid-liquid interface assembly" strategy is reported to generate a non-close-packed AuNP superlattice monolayer (SM) on a centimeter scale for high-performance pentacene-based NFGM. The d and hence the surface plasmon resonance spectra of SM can be tailored by adjusting the molecular weight of tethered polymers. Precise control over the d value allows the successful fabrication of photosensitive NFGM devices with highly tunable performances from short-term memory to nonvolatile data storage. The best performing nonvolatile memory device shows remarkable 8-level (3-bit) storage and a memory ratio over 105 even after 10 years compared with traditional devices with a AuNP amorphous monolayer. This work provides a new opportunity to obtain large area 2D NPs materials with non-close-packed structure, which is significantly meaningful to microelectronic, photovoltaics devices, and biochemical sensors.

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (105) with better endurance (∼2000 cycles) and longer data retention (104 s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.

P-channel differential multiple-time programmable memory cells by laterally coupled floating metal gate fin field-effect transistors

In this paper, we present a new differential p-channel multiple-time programmable (MTP) memory cell that is fully compatible with advanced 16 nm CMOS fin field-effect transistors (FinFET) logic processes. This differential MTP cell stores complementary data in floating gates coupled by a slot contact structure, which make different read currents possible on a single cell. In nanoscale CMOS FinFET logic processes, the gate dielectric layer becomes too thin to retain charges inside floating gates for nonvolatile data storage. By using a differential architecture, the sensing window of the cell can be extended and maintained by an advanced blanket boost scheme. The charge retention problem in floating gate cells can be improved by periodic restoring lost charges when significant read window narrowing occurs. In addition to high programming efficiency, this p-channel MTP cells also exhibit good cycling endurance as well as disturbance immunity. The blanket boost scheme can remedy the charge loss problem under thin gate dielectrics.

Selective control of multiple ferroelectric switching pathways using a trailing flexoelectric field.

Flexoelectricity is an electromechanical coupling between electrical polarization and a strain gradient 1 that enables mechanical manipulation of polarization without applying an electrical bias2,3. Recently, flexoelectricity was directly demonstrated by mechanically switching the out-of-plane polarization of a uniaxial system with a scanning probe microscope tip3,4. However, the successful application of flexoelectricity in low-symmetry multiaxial ferroelectrics and therefore active manipulation of multiple domains via flexoelectricity have not yet been achieved. Here, we demonstrate that the symmetry-breaking flexoelectricity offers a powerful route for the selective control of multiple domain switching pathways in multiaxial ferroelectric materials. Specifically, we use a trailing flexoelectric field that is created by the motion of a mechanically loaded scanning probe microscope tip. By controlling the SPM scan direction, we can deterministically select either stable 71° ferroelastic switching or 180° ferroelectric switching in a multiferroic magnetoelectric BiFeO3 thin film. Phase-field simulations reveal that the amplified in-plane trailing flexoelectric field is essential for this domain engineering. Moreover, we show that mechanically switched domains have a good retention property. This work opens a new avenue for the deterministic selection of nanoscale ferroelectric domains in low-symmetry materials for non-volatile magnetoelectric devices and multilevel data storage.

Van der Waals interfacial bonding and intermixing in GeTe-Sb2Te3-based superlattices

Interfacial phase change memory (iPCM) based on GeTe and Sb2Te3 superlattices (SLs) is an emerging contender for non-volatile data storage applications. A detailed knowledge of the atomic structure of these materials is crucial for further development of SLs and for a better understanding of the resistivity switching characteristics of iPCM devices. In this work, crystalline GeTe-Sb2Te3-based SLs, produced by pulsed laser deposition onto a Si(111) substrate at temperatures lower than in previous studies, are analyzed by advanced scanning transmission electron microscopy. The results reveal the formation of Ge-rich Ge(x+y)Sb(2–y)Tez building blocks with specific numbers of ordered Ge cation layers (between 1 and 5) and disordered cation layers (4) for z = 6–10, as well as intermixed cation layers for z = 5, within the SLs. The G Ge(x+y)Sb(2–y)Tez units are separated from the Sb2Te3 building blocks by van der Waals gaps. In particular, the interlayer bonding is promoted by the formation of outermost cation layers consisting of intermixed GeSb within the building blocks adjacent to the van der Waals gaps. The Ge(x+y)Sb(2–y)Tez units with z > 5 retain metastable crystal structures with two-dimensional bonding within the SLs. The present study shed new light on the possible configurations of the building units that can be formed during the synthesis of GeTe-Sb2Te3-based iPCM materials. In addition, a possible switching mechanism active in iPCM materials is discussed.

Recovering disk storage metrics from low‐level trace events

SummaryBlock devices such as magnetic disks are nonvolatile data storage devices that transfer data in fixed‐size chunks. They are the main nonvolatile memory that holds the file system, and they are also used in virtual memory mechanisms such swapping and page fault handling. Investigating storage performance issues requires a full insight into the operating system internals. Kernel tracing offers an efficient mechanism to gather information about the storage subsystem at runtime. Still, the tracing output is often huge and difficult to analyze manually.In this paper, we introduce a framework to compute meaningful storage performance metrics from low‐level trace events generated by LTTng. A stateful approach is used to model the state of the storage subsystem. Efficient data structures and algorithms are proposed to offer a reasonable response time, allowing the user to navigate throughout the trace and to retrieve metrics from any time range. The framework includes a visualization system that provides different graphical views that represent the collected information in a convenient way. These views are synchronized together, forming a comprehensive perspective that makes storage performance investigation a much more comfortable task. Different use cases are presented to show the usefulness of the framework in real‐world applications.

Recent Advances of Flexible Data Storage Devices Based on Organic Nanoscaled Materials.

Following the trend of miniaturization as per Moore's law, and facing the strong demand of next-generation electronic devices that should be highly portable, wearable, transplantable, and lightweight, growing endeavors have been made to develop novel flexible data storage devices possessing nonvolatile ability, high-density storage, high-switching speed, and reliable endurance properties. Nonvolatile organic data storage devices including memory devices on the basis of floating-gate, charge-trapping, and ferroelectric architectures, as well as organic resistive memory are believed to be favorable candidates for future data storage applications. In this Review, typical information on device structure, memory characteristics, device operation mechanisms, mechanical properties, challenges, and recent progress of the above categories of flexible data storage devices based on organic nanoscaled materials is summarized.

Development of a Measurement Software for the Characterization of WORM Devices for Novel Memory Storage Applications

We hereby propose a software solution to perform high quality electrical measurements for the characterization of WORM (write-once read many), a new generation memory device which is being intensively studied for non-volatile data storage. The as-proposed software is completely based on .NET framework and sample C# code. The paper performed a relevant measurement based on this software. Working WORM devices, based on a polymeric matrix embedded with gold and copper sulfide nanoparticles, have been used for test measurements. The aim of this paper is to show the main steps to develop a fully working measurement software without using any expensive dedicated software.