High Density Data Storage Systems Research Articles

Investigation of magnetic domain interactions and switching mechanism in sputter deposited Fe–Co–Al thin film

To create a high-density data storage system, a thorough understanding of magnetic domain interactions is essential. In this work, we present a systematic study of magnetic domain state interaction and switching mechanism of Fe–Co–Al films across various thicknesses. Structural analysis confirms the formation of an A2-type disorder structure. Magnetic investigation reveals that all films are soft magnetic in nature, exhibiting a predominant in-plane magnetic anisotropy with a low coercive field that increases from 1.9 mT to 3 mT as the film thickness grows from 5 nm to 25 nm. Analysis of first-order reversal curves reveals the formation of multi-domain (MD) states. An enhancement of magnetic domain interactions occurs as the contour graph shifts along the coercive field direction with an increase in film thickness. Switching field distribution (SFD) analysis reveals broader SFD curves, indicating more inter-grain interactions as magnetostatic interactions between magnetic grains intensify with thickness. Further, magnetic force microscopy analysis confirms the presence of MD structures in all films. Magnetization reversal dynamics elucidates domain wall pinning near to zero field and possesses a large out-of-plane switching field. Simulations are performed to corroborate experimental findings. These findings underscore the critical role of domain state configuration and switching mechanisms for designing spintronic devices using soft magnetic thin films.

The b-symbol weight hierarchy of the Kasami codes

The symbol-pair read channel was first proposed by Cassuto and Blaum. Later, Yaakobi et al. generalized it to the b-symbol read channel. It is motivated by the limitations of the reading process in high density data storage systems. One main task in b-symbol coding theory is to determine the b-symbol weight hierarchy of codes. In this paper, we study the b-symbol weight hierarchy of the Kasami codes, which are well known for their applications to construct sequences with optimal correlation magnitudes. The complete symbol-pair weight distribution of the Kasami codes is determined.

MDS Constacyclic Codes and MDS Symbol-Pair Constacyclic Codes

Symbol-pair codes are used to protect against symbol-pair errors in high density data storage systems. One of the most important tasks in symbol-pair coding theory is to design MDS codes. MDS symbol-pair codes are optimal in the sense that such codes attain the Singleton bound. In this paper, a new class of MDS symbol-pair codes with code-length $5p$ and optimal pair distance of 7 is established. It is shown that for any prime $p \equiv 1 \pmod 5$ , we can always construct four $p$ -ary MDS symbol-pair cyclic codes of length $5p$ of largest possible pair distance 7. We also completely determined all MDS symbol-pair and MDS $b$ -symbol codes of length $p^{s}$ and $2p^{s}$ over $\mathbb F_{p^{m}}+u\mathbb F_{p^{m}}$ by filling in some missing cases, and rectifying some gaps in Type 3 codes of recent papers. As an applications of our results, we use MAGMA to provide many examples of new MDS codes over $\mathbb F_{p^{m}}$ and $\mathbb F_{p^{m}}+u\mathbb F_{p^{m}}$ .

Tailoring the dielectric and magnetic properties of Eu-substituted BiFeO3 nanoparticles

A systematic investigation into the enhanced dielectric and magnetic properties of europium - doped bismuth ferrite (Bi(1-x)EuxFeO3, x = 0.0–0.3) multiferroic nanoparticles highlights its usefulness for device miniaturization and high-density data storage systems in nanoelectronics. The samples were synthesized by sol–gel method and calcined at 873 K. Structural characterization by X-ray diffraction and transmission electron microscopy showed the distribution of nanocrystallites with narrow size distribution and further revealed a transformation of the crystalline structure from the initial rhombohedra (R3c) to an orthorhombic (Pn21a) one. This was also accompanied by significant lattice contraction and the elemental composition for each Eu-incorporation was examined through energy dispersive analysis of X- Rays (EDAX). The EDAX studies clearly confirmed the successful and accurate incorporation of Eu3+ in place of Bi3+ and the presence of oxygen vacancies in the samples. Sample with × = 0.2 showed the maximum value of dielectric constant ε′ and leakageε′′ as well as a.c. conductivity(σ). Magnetic response studies reflected the enhancement of spontaneous magnetization by Eu-doping. The maximum values of saturation magnetization MS, remnant magnetization (Mr), and coercivity (HC) were again obtained for the sample with ×= 0.2. The studies thus demonstrate a doping concentration at which the material properties can be optimized for the best performance through substitution and size-controlled crystallization to nanometer dimensions.

Bounds and Constructions of Codes Over Symbol-Pair Read Channels

Cassuto and Blaum recently studied the symbol-pair channel, a model where every two consecutive symbols are read together. This special channel structure is motivated by the limitations of the reading process in high density data storage systems, where it is no longer possible to read individual symbols. In this new paradigm, the errors are not individual symbol errors, but rather symbol-pair errors , where at least one of the symbols is erroneous. In this work, we study bounds and constructions of codes over the symbol-pair channel. We extend the Johnson bound and the linear programming bound for this channel and show that they improve upon existing bounds. We then propose new code constructions that improve upon existing results for pair-distance six, seven, and ten.

On the design of spectrum shaping codes for high-density data storage

This paper proposes systematic code design methods for constructing efficient spectrum shaping codes with the maximum runlength limited constraint k, which are widely used in data storage systems for digital consumer electronics products. Through shaping the spectrum of the input user data sequence, the codes can effectively circumvent the interaction between the data signal and servo signal in high-density data storage systems. In particular, we first propose novel methods to design high-rate k constrained codes in the non-return-to-zero (NRZ) format, which can not only facilitate timing recovery of the storage system, but also avoid error propagation during decoding and reduce the system complexity. We further propose to combine the Guided Scrambling (GS) technique with the k constrained code design methods to construct highly efficient spectrum shaping k constrained codes. Simulation results demonstrate that the designed codes can achieve significant spectrum shaping effect with only around 1% code rate loss and reasonable computational complexity.

Flexible multi-level resistive memory with high current ratio by electrical triggering into insulating layer

We demonstrate a flexible multi-level resistive memory device, based on the concept of electrical triggering into an insulating layer, which exhibits a high current ratio between two memory states in the unipolar mode of operation. Due to the presence of a triggering zone in unit memory cell, three resistive memory states having different domain sizes of the conductive filaments are achieved. Each memory state is readable without the disturbances by other states and the current ratio is as high as 103. The multi-level memory states are found to be well preserved during bending and applicable for constructing flexible and high-density data storage systems.

Constructions and Decoding of Cyclic Codes Over <inline-formula> <tex-math notation="LaTeX">$b$ </tex-math> </inline-formula>-Symbol Read Channels

Symbol-pair read channels, in which the outputs of the read process are pairs of consecutive symbols, were recently studied by Cassuto and Blaum. This new paradigm is motivated by the limitations of the reading process in high density data storage systems. They studied error correction in this new paradigm, specifically, the relationship between the minimum Hamming distance of an error correcting code and the minimum pair distance, which is the minimum Hamming distance between symbol-pair vectors derived from codewords of the code. It was proved that for a linear cyclic code with minimum Hamming distance d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> , the corresponding minimum pair distance is at least d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> +3. In this paper, we show that, for a given linear cyclic code with a minimum Hamming distance d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> , the minimum pair distance is at least d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> + (dH/2). We then describe a decoding algorithm, based upon a bounded distance decoder for the cyclic code, whose symbol-pair error correcting capabilities reflect the larger minimum pair distance. Finally, we consider the case where the read channel output is a larger number, b ≥3, of consecutive symbols, and we provide extensions of several concepts, results, and code constructions to this setting.

Non‐volatile memories: Materials, nanostructures and integration approaches

Dear reader, The following pages are the result of the exciting investigations presented during the Symposium AA of the 2015 E-MRS Spring Conference “Non-volatile memories: materials, nanostructures and integration approaches”, aimed to gather the newest and most significant studies in the field of materials and materials-related concepts for non-volatile memories (NVM), devices at the heart of all appliances that need to handle and keep information during power cycling. The increasing need for high density data storage systems in different types of applications has created a significant research effort to develop memory concepts using novel functional materials. Improving the scalability and performance of these new devices is a multi-disciplinary task, which spans from molecular dynamics to solid state physics, to manufacturing process. These aspects make the NVM field most appealing to the research related to materials with application potential, making the conference an excellent platform to share, make visible and disseminate the work done in this field in Europe and beyond. The topics covered were from the basic science to the materials research challenges, as well as key integration strategies for future technologies. Contribution areas included semiconductor-based memories, flash magnetic memories, ferroelectric systems, chalcogenide- based phase change memory, resistive RAM featuring novel dielectrics and neuromorphic concepts, conductive bridge RAM based on innovative nanostructured configurations and oxide stacks. These subject areas were presented as oral and poster contributions and are nicely represented by the papers of this special issue, which includes four featured articles discussing the recent progress in peripheral CMOS devices for DRAM 1, the reliability of electrochemical metallization memories and conductive bridge RAM as linked with their selected device structures 2, a modelling investigation to understand the role of the material properties of oxide-based resistive RAM devices on the electrical behaviour at circuit level 3, and a new concept to extend the life of planar NAND beyond the 20 nm node, namely hybrid floating gate 4. Topics were motivated with presentations of experts of each subject. We are thankful to their participation as they helped to invigorate the discussion among the participants. Their names are Alessio Spessot (Micron), Ilia Valov (Research Center Jülich), Julie Grollier (CNRS/Thalès), Luca Larcher (Università di Modena e Reggio Emilia), Marco Bernasconi (Università di Milano Bicocca), Paolo Cappelletti (Micron) and Robin Roelofs (ASM). The symposium owes a great deal of gratitude to all the scientists who helped in the revision of the submitted abstracts, giving their expert opinion and generous time, allowing us to have a Symposium of great quality. Here are their names: Alex Kotov, Andrea Fantini, Christian Walczyk, Claudia Wiemer, Damien Querlioz, Daniele Ielmini, Etienne Janod, Gabriele Navarro, Hilde Hardtdegen, Jaakko Akoda, Juergen Schubert, Laurent Vila, Lucian Prejebeanu, Magali Putero, Robert Muller, Roberto Fallica, Sabina Spiga, Stephane Mangin and Valeri Afanas'ev. We would also like to thank the students that helped in the organization, namely: Simone Selmo (CNR, Italy), Michael Chen (imec, Belgium) and Adrien Le Goff (University of Paris Sud, France). Finally, the Symposium would not have been possible without the financial support of E-MRS headquarters and the sponsorship of Micron Foundation. Judit G. Lisoni On behalf of the Guest Editors Damien Deleruyelle, Ludovic Goux, Massimo Longo, Dafiné Ravelosona

Multiferroism in rare earth metals-doped BiFeO3 nanowires

Nanowires are the key multifunctional materials for the development towards device miniaturization and high-density data storage systems for future nanoelectronics. In the present report, multifunctional undoped and rare earth metals ions (Gd3+, Tb3+, Dy3+)-doped BiFeO3 nanowires with 20nm diameter, have been synthesized by template-assisted colloidal dispersion technique. The effect of the size of synthesized nanowires, as well as, the doping of rare earth ions on the structural, magnetic, dielectric and magnetodielectric properties have been studied. The doping of rare earth metals ions leads to structural transition from rhombohedral to orthorhombic BiFeO3 nanowires. The synthesized nanowires exhibit ferromagnetic nature with high value of saturation magnetization, dielectric constant and magnetodielectric coefficient.

Blue laser-sensitized photopolymer for a holographic high density data storage system

We present a new blue-sensitized photopolymer to achieve a higher storage density compared to green/red-recordable media. Photopolymers are prepared based on a two-chemistry system and their holographic recording properties are investigated. A matrix of long and flexible ether units of an epoxy precursor and a multi-crosslinkable amine hardener enhances energetic sensitivity and suppresses volume shrinkage effectively. Page-wise recording of 961 bits/page of digital data is demonstrated and long term recording stability is also verified for a period of roughly 2 months.

Jitter-free multi-layered nanoparticles optical storage disk with buffer ring

A multi-layered nanoparticles optical disk has been developed for a jitter-free high-density data storage system. The disk has nano structures composed of 300-nm-diameter photosensitive particles and 30-nm-width non-photosensitive buffer rings around them. With the buffer rings into the nanoparticles disk, a conventional confocal microscope equipped with a low numerical aperture (NA) objective picked up a particle's shape signal to generate a synchronous signal on its own. In the three-dimensional structured disk proposed, no electronically-produced reference signal is necessary for clock data recover (CDR); no jitter occurs in data decoding.

Data-Aided Timing Recovery for Recording Channels With Data-Dependent Noise

In high-density data storage systems, noise becomes highly correlated and data dependent as a result of media noise, channel nonlinearities, and front-end filters. In such environments, conventional timing recovery schemes will exhibit large residual timing jitter and, especially, data-dependent timing jitter. This paper presents a new data-aided timing recovery algorithm for data storage systems with data-dependent noise. We derive a maximum-likelihood timing recovery scheme based on a data-dependent Gauss-Markov model of the noise. The timing recovery algorithm incorporates data-dependent noise prediction parameters in the form of linear prediction filters and prediction error variances. Moreover, because noise can be nonstationary in practice, we propose an adaptive algorithm to estimate and track the noise prediction parameters. Simulation results, for an idealized optical storage channel incorporating a simple model of media noise, illustrate the merits of our algorithm

A Photochromic Liquid Crystal System

ABSTRACT Switching molecular or supramolecular systems reversibly from one state to another, with both states having significantly different properties using light is widespread in biological systems and has been in the focus of materials research for many years. Such synthetic systems are promising as high density data storage systems, sensors, photonic switches or as molecular logic gates. There the concept of optically addressable molecules promises miniaturisation to the molecular level and potentially the direction towards optical computing on that level. Our approach is based on the concept that the functional groups and the properties in such molecules, if suitably selected can add up to attractive properties in the self-assembled molecular systems. Rational design allows of the photochromic core and the mesogenic groups for the modulation of the photochromic behaviour, the absorption properties, the quantum yields of the photo conversion processes and the conversion obtained at the photostationary state. The use of suitable mesogens allows for the use of the FRET effect for the switching behaviour. Keywords: liquid crystal, molecular switch, photochromic, self-assembly, spectroscopy, FRET, nematic, Smectic C, diarylethene

Decoding for iterative Reed-Solomon coding schemes

For high density data storage systems channel errors may appear in the form of bursts. This error correlation can significantly degrade the bit error rate on the subsequent stages of data processing. To correct error bursts the interleaved Read-Solomon (RS) codes are used. Usually, after the deinterleaving, the received words are decoded one by one by the same error correction algorithm. In this paper, a novel approach for the decoding of interleaved codes is proposed. It is based on a notion of covering error locators that locate error positions in two or more adjacent words. To compute the covering error locator polynomial, a modification of the Berlekamp-Massey algorithm is proposed. It is shown that with a certain probability of failure the proposed algorithm can correct more errors than the designed error correction ability. The algorithm may also be useful in a more general case of interleaved coding schemes with both rows and columns encoded by RS code.

Persistent spectral hole burning of Sm2+ in borate glasses

It is expected that persistent spectral hole burning (PSHB) will be applied for a high-density data storage system and it can serve as a powerful method for studying the local structure around optical centers. The authors' group has discovered a room-temperature PSHB material for Sm2+-doped glasses. The present work investigated the relationship between the Debye temperature of the glass and the hole width, and the effects of alkali ions on hole burning for alkali borate glasses. Sm2+-doped glasses were produced in a strongly reducing atmosphere. Hole burning was measured for the 5D0-7F0 transition of the Sm2+ ion. The hole width decreased with increasing Debye temperature which is a parameter of the bond strength of glass network former. The hole width for borate glasses was more closely related to the local structure around the Sm2+ ion than to the glass matrix. The hole depth increased with increasing optical basicity of glasses. The hole burning mechanism in Sm2+-doped glasses seemed to be the photo-ionization of Sm2+ → Sm3+ + e−.

Optics and magneto-optics of thin metallic films

In recent years there has been a rapid growth in the study of the optical and magneto-optical properties of many different conducting, semiconducting and magnetic materials. Whilst this growth owes much to a basic utilitarian interest in the production of various devices, for example, complex multilayer optical devices with special reflection, interference and polarization properties and high density data storage systems utilizing different magneto-optic effects, the extensive study of fundamental optical and magneto-optical effects has also helped considerably in the understanding of both the electronic structures of solids and unusual magnetization reversal processes in some new magnetic materials.