Use In Memory Devices Research Articles

Creating arbitrary sequences of mobile magnetic skyrmions and antiskyrmions

Magnetic skyrmions and their antiparticles, the antiskyrmions, are stable magnetic solitons existing down to the nanometer scale. Their stability and size as well as the possibility to propel them by, e.g., electric currents make them promising candidates for use in memory devices, such as racetrack memories. Skyrmions and antiskyrmions share those same advantages individually, but may annihilate each other when they coexist in the same device. Yet, combining them to represent logical bits of 0 (skyrmion) and 1 (antiskyrmion) in one device opens new possibilities to create new types of densely packed racetrack memory devices. For this, a controlled creation and annihilation procedure, i.e., a writing or deletion operation, is necessary. Here, we propose a method to create arbitrary sequences of coexisting skyrmions and antiskyrmions by rotations of the magnetic moments at the edge of a rectangular slab. The skyrmions and antiskyrmions remain stable and do not annihilate each other.

Switching to Hidden Metallic Crystal Phase in Phase-Change Materials by Photoenhanced Metavalent Bonding.

Metavalent bonding is crucial for the determination of phase transition and improvement of device performance in phase-change materials, which are attracting interest for use in memory devices. Although monitoring dielectric and phononic parameters provides a direct measure of the metavalent bonding, the control of phase-change phenomena and metavalent bonding in the dynamical regime has yet to be demonstrated. This study reports the photoenhanced metavalent bonding and resulting hidden metallic crystalline state of Ti-doped Sb2Te3, a representative phase-change material with ultralong sustainability. Using ultrafast terahertz spectroscopy, Ti0.4Sb2Te3 was discovered to possess ultralong pump-probe dynamics, which is retained over hundreds of picoseconds, unlike the short-lived state of undoped Sb2Te3. Moreover, for Ti0.4Sb2Te3 during the long-lived transmission change, the infrared-active phonon is highly softened, even more than the amount of a thermal phonon shift, indicating the photoenhancement of lattice anharmonicity. Such a long-lived relaxation implies photoinduced transition into a crystalline state of ultrastrong metavalent bonding in Ti0.4Sb2Te3, on the basis of comparisons of the dynamical dielectric constant and temporal phonon shift. Our results show the realization of photoengineering of phase-change materials by tuning electron sharing or transferring.

PCoSA: A product error correction code for use in memory devices targeting space applications

The radiation sensitivity of integrated memory cells increases dramatically as the supply voltage decreases. Although there are some Error Correcting Code (ECC) studies to prevent faults on memories used in space applications, there is no consensus on choosing the best ECC product-type with two-dimensional Hamming to mitigate data faults in memory. This work introduces the Product Code for Space Applications (PCoSA), an ECC product based on Hamming and parity in both rows and columns for use in memory with space-application reliability requirements. The potentialities of PCoSA were evaluated by injecting (i) thirty-six error patterns already available in the literature and (ii) all possible combinations of up to seven bitflips. PCoSA has corrected all cases of the thirty-six error patterns, and it has a correction rate of 100% for any three bitflips, 82.67% for four bitflips, and 69.7% for five bitflips.

Designing Thermally Actuated Bimorph as Energy Harvester

Abstract Microelectromechanical systems (MEMS) are micrometre-size systems that are capable of transforming electrical signals to mechanical signals. In this paper, the use of MEMS devices as a method for harvesting waste heat is explored. A background for the technology and methods is discussed and a method proposed for a working device based upon a thermally heated bimorph actuated by waste radiation alone is investigated. A chopper interrupts the radiant energy inducing an oscillation in the bimorph temperature and thus creates a mechanical motion which can be taken advantage of using piezoelectric materials. Difficulties in harvesting radiant energy with this method are highlighted and suggestions for non-passive energy generation are made based on the outlined principles.

Characterization techniques to predict mechanical behaviour of green ceramic bodies fabricated by ceramic microstereolithography

Ceramic microstereolithography (CMSL) has emerged as solid free form (SFF) fabrication technology in which complex ceramic parts are fabricated from ceramic suspensions which are formulated by dispersing ceramic particles in UV curable resins. Ceramic parts are fabricated by exposing ceramic suspension to computer controlled UV light which polymerizes resin to polymer and this polymer forms rigid network around ceramic particles. A 3-dimensional part is created by piling cured layers one over the other. These ceramic parts are used to build microelectromechanical (MEMS) devices after thermal treatment. In many cases green ceramic parts can be directly utilized to build MEMS devices. Hence characterization of these parts is essential in terms of their mechanical behaviour prior to their use in MEMS devices. Mechanical behaviour of these green ceramic parts depends on cross link density which in turn depends on chemical structure of monomer, concentrations of photoinitiator and UV energy dose. Mechanical behaviour can be determined with the aid of nanoindentation. And extent of crosslinking can be verified with the aid of DSC. FTIR characterization is used to analyse (-C=C-) double bond conversion. This paper explains characterization tools to predict the mechanical behaviour of green ceramic bodies fabricated in CMSL

Water-Erasable Memory Device for Security Applications Prepared by the Atomic Layer Deposition of GeO2

We have investigated the atomic layer deposition (ALD) of GeO2 thin films that dissolve in water rapidly and have excellent electrical properties for use in memory devices. The growth characteristics based on surface reactions during the ALD process are discussed by correlation with experimental results and atomistic theoretical calculation. Compared to sputtered GeO2 films, the ALD-grown GeO2 is perfect, pure, and water-soluble at room temperature and has better electrical properties for use as the dielectric layer in memory devices. The superior film properties of ALD GeO2 are attributed to the higher film density, high purity, low roughness, and highly stoichiometric film composition. Finally, we demonstrate the fabrication of charge-trapping memory (CTM) devices with ALD GeO2, and that the electrical information stored in the CTM can be eliminated immediately by exposure to one droplet of water at room temperature. Thus, ALD GeO2 could find widespread application in the fabrication of secure memory de...

The Influence of Alkali Metal Chloride Treatments on the Wear Resistance of Silicon Surfaces for Possible Use in MEMS

ABSTRACTThe wear of contacting silicon surfaces in microelectromechanical systems (MEMS) has been a longstanding concern. To address this issue, the effects of immersing silicon surfaces into alkali metal chloride solutions (LiCl, NaCl, CsCl) on their sliding friction and wear were investigated. A custom-built reciprocating tribometer was used with a sapphire ball as the counterbody. Results indicated that the friction coefficient between the silicon surface (p-doped, orientation (100)) and a sapphire ball can be reduced by up to 30% by treating the silicon surfaces in aqueous salt solutions (concentration 1 mol/L, exposure for 24 h). These modified surfaces also have higher wear resistance and a significant change in wettability. After immersion, the contact angle between the silicon surface and water was reduced by approximately 50%. These results may lead to new, simple, and inexpensive methods to increase the wear resistance of silicon surfaces for use in MEMs devices.

Design and analysis of codes with distance 4 and 6 minimizing the probability of decoder error

The problem of minimization of the decoder error probability is considered for shortened codes of dimension 2m with distance 4 and 6. We prove that shortened Panchenko codes with distance 4 achieve the minimal probability of decoder error under special form of shortening. This shows that Hamming codes are not the best. In the paper, the rules for shortening Panchenko codes are defined and a combinatorial method to minimize the number of words of weight 4 and 5 is developed. There are obtained exact lower bounds on the probability of decoder error and the full solution of the problem of minimization of the decoder error probability for [39,32,4] and [72,64,4] codes. For shortened BCH codes with distance 6, upper and lower bounds on the number of minimal weight codewords are derived. There are constructed [45,32,6] and [79,64,6] BCH codes with the number of weight 6 codewords close to the lower bound and the decoder error probabilities are calculated for these codes. The results are intended for use in memory devices.

High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. This result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

Microstructure and nanomechanical properties of Mn-rich Ni–Mn–Ga thin films

We report the effect of post-annealing on the crystalline phase, grain growth, magnetic and mechanical properties of Ni–Mn–Ga thin films deposited at room temperature followed by post-annealing at different temperatures. The phase and microstructural analysis reveal that amorphous to crystalline transformation occurs in as-deposited films after post-annealing above 873 K. The transformation of disordered phase into nanocrystalline phase by the influence of annealing has been confirmed by transmission electron microscopy. The crystalline films exhibit soft magnetic behavior with the Curie temperature of 314 K, while the amorphous films exhibit the Pauli-paramagnetic behavior even down to 4 K. The mechanical properties like hardness and elastic modulus of the films also show a strong dependence on the annealing temperature with crystalline film exhibiting maximum values of 6 GPa and 103 GPa, respectively. The Ni–Mn–Ga film annealed at 873 K exhibits enhanced nanomechanical properties and room temperature ferromagnetism which make this a potential candidate for use in MEMS devices.

Antipsychotic treatment dosing profile in patients with schizophrenia evaluated with electronic monitoring (MEMS®)

BackgroundAlthough the Medication Event Monitoring System (MEMS®) device offers accurate information on treatment dosing profile, such profile has never been studied in patients with schizophrenia. Enhancing our knowledge on this issue would help in developing intervention strategies to improve adherence to antipsychotic treatment in these patients. Methods74 outpatients with schizophrenia were monitored with the MEMS device for a 3-month period, for evaluation of antipsychotic treatment dosing profile, possible influence of medication schedule-related variables, adherence to treatment – considering dose intake within prescribed timeframes – and possible Hawthorne's effect of using the MEMS device. ResultsDose-omission gaps occurred in 18.7% of monitoring days, most frequently during weekends, almost significantly. Almost one-third of prescribed doses were taken out of prescribed time. Neither the prescribed number of daily doses nor the indicated time of the day for dose intake (breakfast, dinner), were associated with correct antipsychotic dosing. Excess-dose was rare in general, and more frequent out of prescribed dose timeframe. No Hawthorne's effect was found for the MEMS device. Adherence reached only 35% according to a definition that included dose intake within prescribed timeframes. ConclusionsAntipsychotic treatment dosing was considerably irregular among patients with schizophrenia. Strategies to reduce dose-omission gaps and increase dosing within prescribed timeframes seem to be necessary. Gaining knowledge on precise oral antipsychotic dosing profiles or the influence of schedule-related variables may be useful to design strategies towards enhancing adherence. There appears to be no Hawthorne's effect associated with the use of MEMS devices in outpatients with schizophrenia.

Numerical analysis for design optimization of microcantilever beams for measuring rheological properties of viscous fluid

The precise measurement of rheological properties is a demanding problem in various field of engineering. Occasionally the available sample volume of interest may be sufficiently small where the conventional methods of measuring rheological properties are inappropriate. Consequently, there is a growing interest in the use of MEMS devices to measure the required properties, especially with an aim of encouraging high throughput. During this research, the dynamic response of micro cantilever beams is demonstrated to characterize the rheological properties of viscous materials. First, the dynamic response of a mini cantilever beam partially submerged in air and water is measured experimentally for different configurations using a duel channel PolyTec scanning vibrometer. Next, finite element analysis (FEA) method is implemented to predict the dynamic response of the same cantilever beam in air and water, and then compared with corresponding experiments. Once the model is validated, further numerical analysis is conducted to investigate the variation in modal response with changing beam dimension and fluid properties. Results obtained from this parametric study can be used for sensitivity analysis and to design the optimized MEMS based test set up for measuring the rheological properties of viscous fluid and of any soft viscoelastic materials such as biofilm. Miniaturization of the measuring instrument is necessary so that small sample volume can be used to perform the desired test.

Polyimide memory: a pithy guideline for future applications

Polymeric materials for use in memory devices have attracted significant scientific interest due to their several advantages, such as low cost, solution processability, high mechanical strength, and possible development of three-dimensional stacking devices. Taking into account the heat resistance for the device fabrication process, polyimides (PIs) are one of the most attractive polymers for memory applications due to their high thermal stability and mechanical strength. In recent years, a large number of studies have revealed that almost all kinds of memory properties from volatile to non-volatile memory can be produced by optimizing the chemical structure of the PIs. Several mechanisms have been discussed in order to explain the switching properties. Among them, two major theories, field induced charge transfer (CT) and filament formation, are thought to explain the phenomena in the PI system. In this article, recent studies of functional polyimides (PIs) for memory applications are reviewed, mostly focusing on the mechanism underlying the switching phenomena. In addition, some progress in the fabrication process for developing high density storage will also be reviewed.

Polarization Switching Behaviour of Metallo-Organic Decomposition Processed (Pb0.60Ca0.40)TiO3 Thin Film Capacitors

Polarization switching behaviours of polycrystalline (Pb0.60Ca0.40)TiO3 thin films deposited on Pt/Ti/SiO2/Si substrate by metallo-organic decomposition technique have been studied in detail. The switching time dependence of the polarization demonstrates the effect of charge injection on the ferroelectric properties of the film. Typically, the upper limit of the polarization switching time of these films free from charge injection is ∼20 ms. The (Pb0.60Ca0.40)TiO3 film with simple Pt top and bottom electrodes exhibits ferroelectric properties with spontaneous polarization Ps∼19 μc/cm2, remanent polarization Pr∼11.8 μc/cm2 and coercive field Ec∼167 kV/cm and fatigue free behavior up to ∼5.3 × 105 read/write cycles. Although the observed value of Ec and fatigue free behavior up to 105 read/write cycles of these (Pb0.60Ca0.40)TiO3 films are not promising for their use in memory devices, no systematic study of the polarization switching properties of (Pb0.60Ca0.40)TiO3 films has been discussed earlier in the literature.

Synthesis and characterization of polyimide‐γ‐Fe2O3 nanocomposites

AbstractNovel polyimide‐γ‐Fe2O3 hybrid nanocomposite films (PI/γ‐Fe2O3) has been developed from the poly(amic acid) salt of oxydianiline with different weight percentages (5, 10, 15 wt %) of γ‐Fe2O3 using tetrahydrofuran (THF) and N,N‐dimethylacetamide (DMAc) as aprotic solvents. The prepared polyimide‐γ‐Fe2O3 nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), transmission electron micrograph (TEM), X‐ray diffraction (XRD), 13C‐NMR, and thermal analysis (TGA/DSC) techniques. These studies showed the homogenous dispersion of γ‐Fe2O3 in the polyimide matrix with an increase in the thermal stability of the composite films on γ‐Fe2O3 loadings. Magnetization measurements (magnetic hysteresis traces) have shown very high values of coercive force indicating their possible use in memory devices and in other related applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 834–840, 2007

Organic Donor-Acceptor System Exhibiting Electrical Bistability for Use in Memory Devices.

An all-organic electrically bistable device and its application in non-volatile memory is reported. The switching mechanism is attributed to electric-field-induced charge transfer from an organic electron donor to an acceptor, so that the device switches from a low- to a high-conductivity state. This device provides a new direction for data-storage technology based on organic composites.

Modification of drain current on metal–oxide–semiconductor field-effect transistor by magnetic field induced by remanent magnetization

We propose a concept of drain current (Ids) modification in a metal–oxide–semiconductor field-effect transistor (MOSFET) using the Lorentz force from an external magnetic field and a magnetic field induced by remanent magnetization. We fabricated a Pt∕MZF∕YSZ∕MOSFET structure (MZF:Mn0.60Zn0.30Fe2.10O4,YSZ:Y0.15Zr0.85O1.93), based on this concept and examined the effect of the magnetic field on electrical properties. The magnetic field increased the Ids when the carriers were pushed away from the interface. A magnetic field of the opposite direction increased Ids slightly. This phenomenon is related to the potential change and carrier mobility. It may be useful for use in memory devices.

MEMS beams with defects: a model of non-ideal rods using a Cosserat approach for component level modelling

We present and derive a technique for the introduction of defects into a beam model based on the Cosserat theory of rods. The technique is designed for the derivation of component models of non-ideal rods for use in MEMS devices. We also present a worked through example of blob/nick defects (where the rod has an area with an excess/lack of material) and a guide for a model with random pits and blobs along the length of the beam. Finally we present a component level model of a beam with a defect and compare it to results from a finite element analysis simulation. We test the Cosserat model for two cases without any defect and four with a defect. Results are in good agreement with a maximum 0.5% difference for the ideal case and under 1% differences for all but one of the defective cases, the exception being a 2% error in an extreme case for which the model is expected to break down. Overall, the Cosserat model with and without defects provides an accurate way of modelling slender structures. In addition, simulation times are greatly reduced through this approach and further development for both component level models as well as FEA components is important for practical yet accurate modelling of MEMS both for prediction and comparison.

Micro/nanotribological studies of polysilicon and SiC films for MEMS applications

Microelectromechanical (MEMS) devices are currently made from single-crystal silicon, various polysilicon films and other ceramic materials. Silicon carbide (SiC) film has recently been pursued as a material for use in MEMS devices owing to its excellent mechanical properties and high-temperature capabilities. Since surface properties, friction and wear are important issues in such small-scale devices, it is essential that the materials used in MEMS have good micro/nonotribological properties. using atomic force/friction force microscopy (AFM/FFM), surface roughness, microscale friction and microscale scratch/wear resistance of 3CSiC (cubic SiC) films, as well as undoped single-crystal Si(100) and doped and undoped polysilicon films for comparison were measured. Nanohardness and modulus of elasticity were measured using a Nanoindenter. Surface roughness values showed that the as-deposited films of SiC and undoped polysilicon were rougher than the doped polysilicon film and Si(100). Polishing of the as-deposited samples resulted in comparable values of roughness between SiC and undoped and doped polysilicon films, while Si(100) still remained the smoothest and the doped polysilicon film, the roughest. It was found that the polished SiC and doped polysilicon films showed the lowest friction followed by undoped polysilicon film, while Si(100) showed high friction. Microscale scratch/wear studies clearly showed that SiC film was much more scratch/wear resistant than the other materials, which showed comparable resistance levels. SiC also showed higher hardness and modulus of elasticity compared to the other materials. These results show that 3CSiC film posessess desirable micro/nanotribological characteristics that make it an ideal material for use in MEMS devices.

Neural Communication in a Mnemonic Nutshell: A Cognitive Framework That Improves Understanding

L EARNING biology is not easy. As researchers develop an ever more subtle understanding of biological processes, the sheer quantity of information makes it difficult for students to retain enough facts to develop a holistic understanding of the material. The problem is particularly acute in introductory courses where students are exposed to an array of detailed, sometimes disparate, information. Although we know that the students need this information to succeed in advanced courses, the sad reality is that they will forget much of it after the semester. Given the demands upon our students, there are at least two options open to us. First, we can emphasize concept learning over rote memorization whenever possible. Second, when students do need to memorize material, we can restructure the disparate facts so that they relate to things that the students are interested in. For example, the late James V. McConnell of the University of Michigan developed a series of clever stories about the function of various brain structures. He told his classes that the function of the hypothalamus is to control the four Fs of behavior: fighting, fleeing, feeding and mating. Years later, students who have forgotten nearly everything else about biology still recall the functions of this area of the brain. This paper has two goals. The first is to promote the use of memory devices, also known as mnemonics, by outlining six different types that are proven ways to better help students recall information. These mnemonics have been carefully studied by cognitive psychologists (Bower 1970, Loftus 1980, Lorayne & Lucas 1974, Ross & Lawrence 1968), and each is best suited to remembering different types of material. My hope is that this outline will enable teachers to develop new and more effective ways to present complex information. The second goal of this paper is to describe a memory device that I use to help my students more easily recall the process of neural conduction. This device takes the form of an allegory of life on a college campus, and it incorporates many of the mnemonic techniques that I outline. I present this allegory with an experiment I conducted that measured its pedagogical value.