WorldCat Identities

Dieny, B. (Bernard)

Overview
Works: 33 works in 48 publications in 2 languages and 496 library holdings
Roles: Editor, Thesis advisor, Opponent, Author, 956, 958
Publication Timeline
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Most widely held works by B Dieny
Introduction to magnetic random-access memory by R. B Goldfarb( )

7 editions published between 2016 and 2017 in English and held by 265 WorldCat member libraries worldwide

Basic Spintronic Transport Phenomena / Nicolas Locatelli, Vincent Cros -- Magnetic Properties of Materials for MRAM / Shinji Yuasa -- Micromagnetism Applied to Magnetic Nanostructures / Liliana D Buda-Prejbeanu -- Magnetization Dynamics / William E. Bailey -- Magnetic Random-Access Memory / Bernard Dieny, I. Lucian Prejbeanu -- Magnetic Back-End Technology / Michael C. Gaidis -- Beyond MRAM: Nonvolatile Logic-in-Memory VLSI / Takahiro Hanyu, Tetsuo Endoh, Shoji Ikeda, Tadahiko Sugibayashi, Naoki Kasai, Daisuke Suzuki, Masanori Natsui, Hiroki Koike, Hideo Ohno -- Appendix: Units for Magnetic Properties
Magnétisme( Book )

2 editions published between 1999 and 2000 in French and held by 84 WorldCat member libraries worldwide

Magnétisme by Michel Cyrot( Book )

3 editions published between 1999 and 2000 in French and held by 76 WorldCat member libraries worldwide

Brisure du ferromagnétisme dans les systèmes à anisotropie aléatoire : étude de la phase basse température et des propriétés critiques d'alliages amorphes à base de terres rares by Bernard Dieny( Book )

2 editions published in 1985 in French and held by 6 WorldCat member libraries worldwide

ETUDE EXPERIMENTALE DES PROPRIETES A BASSE TEMPERATURE D'UNE SERIE D'ALLIAGES AMORPHES DY::(X)GD::(1-X)NI. DANS CES ALLIAGES LES IONS LANTHANIDES SONT COUPLES FERROMAGNETIQUEMENT ET POSSEDENT UNE DIRECTION D'ANISOTROPIE UNIAXIALE D'ORIENTATION ALEATOIRE. ETUDE PAR MAGNETOMETRIE JOSEPHSON (SQUID), SUSCEPTIBILITE ALTERNATIVE, COUPLES MAGNETIQUES, DIFFUSION DE NEUTRONS ET SIMULATION NUMERIQUE. A BASSE TEMPERATURE L'ANISOTROPIE ALEATOIRE CONDUIT A UNE VERITABLE BRISURE DU FERROMAGNETISME QUI NE SUBSISTE QUE COMME ORDRE LOCAL. MACROSCOPIQUEMENT L'AIMANTATION SPONTANEE A LA SYMETRIE SPHERIQUE. ETUDE DETAILLEE DES HYSTERISIS DIRECTIONNELLLE ET RATIONNELLE. ETUDE DES PROPRIETES DE LA TRANSITION DE PHASE DANS LES CAS EXTREMES DE FAIBLE ET DE FORTE ANISOTROPIE LOCALE (GDNI/DYNI). CES SYSTEMES EN OFFRANT LA POSSIBILITE DE GRADUER LA FRUSTRATION PAR VARIATION DU RAPPORT DE L'ANISOTROPIE ALEATOIRE A L'ECHANGE PERMETTENT DE PASSER CONTINUEMENT DU FERROMAGNETISME AUX VERRES DE SPIN ET FACILITENT DE CE FAIT LA COMPREHENSION DE SYSTEMES MAGNETIQUES DESORDONNES
Special issue: spin electronics( Book )

1 edition published in 2007 in English and held by 3 WorldCat member libraries worldwide

Etude des parois de domaines dans les nanofils magnétiques by Ségolène Jamet( )

1 edition published in 2015 in French and held by 3 WorldCat member libraries worldwide

The work performed during my thesis was based on magnetic domain walls in magnetic nanowires. We extended the phase diagram of domain walls already known to a geometry ranging from nanostrips to nanowires. The various types of domain wall and transition phase types are presented. We introduced new estimators based on physical known features, in order to better characterize domain walls magnetic configurations of domain walls and then to predict the type of domain wall according to the geometry.To validate our theoretical approach, we were interested in imaging these domain walls. We chose the X-ray Magnetic Circular Dichroism along with the PhotoEmission Electron Microscopy (XMCD PEEM). This microscopy method enables to reach spatial resolution required to observed domain wall configuration. The experimental conditions (sample and set up) enable to have access both the surface magnetization and also the shadow of the wire projected on to the substrate. This enable caries information about volume magnetization, averaged along the path of the X-ray through the wire. This experimental configuration gives rise to complex contrasts. Thus, we developped a model that enables to simulate the XMCD contrast from steady state micromagnetic configurations. Comparison between experimental and simulated contrasts gives rise to a good quantitative agreement. Moreover, experimental parameters were studied in order to get the best magnetic contrast, reflecting the true magnetic configuration of the sample.For the future, the work consists in the study of the domain wall propagation in nanowires, particularly the propagation of the Bloch point wall
Mémoire magnétique à écriture assistée thermiquement à base de FeMn by Erwan Gapihan( )

1 edition published in 2011 in French and held by 3 WorldCat member libraries worldwide

This thesis addresses a current topic of TA-MRAM, new non volatile memories using pulses to heat and thus allows the reversal of the magnetization of a ferromagnetic layer. A first goal was to learn the writing mechanism (heating) of TA-MRAM cells. Therefore, we compared electrical measurements and thermal simulations. Generally speaking, TA-MRAM combines two ferromagnetic layers where the relative direction of the magnetization is pinned by antiferromagnetic layers. Moreover, we developed new magnetic tunnel junctions using FeMn in the storage layer. We thus optimized the ferromagnetic and antiferromagnetic layers of the storage layer in order to minimize the magnetic field needed to reverse the magnetization of these layers and thus to decrease the power consumption. To finish, the etching of magnetic memory dots is explored, giving the pattern key of magnetic devices
Conception sur mesure d'un FPGA durci aux radiations à base de mémoires magnétiques by Olivier Gonçalves( )

1 edition published in 2013 in French and held by 3 WorldCat member libraries worldwide

Le but de la thèse a été de montrer que les cellules mémoires MRAM présentent de nombreux avantages pour une utilisation en tant que mémoire de configuration pour les architectures reconfigurables et en particulier les FPGAs (Field Programmable Gate Arrays). Ce type de composant est programmable et permet de concevoir un circuit numérique simplement en programmant des cellules mémoires qui définissent sa fonctionnalité. Un FPGA est principalement constitué de cellules mémoires. C'est pourquoi elles déterminent en grande partie ses caractéristiques comme sa surface ou sa consommation et influencent ses performances comme sa rapidité. Les mémoires MRAM sont composées de Jonctions Tunnel Magnétiques (JTMs) qui stockent l'information sous la forme d'une aimantation. Une JTM est composée de trois couches : deux couches de matériaux ferromagnétiques séparées par une couche isolante. Une des deux couches ferromagnétiques a une aimantation fixée dans un certaine direction (couche de référence) tandis que l'autre peut voir son aimantation changer dans deux directions (couche de stockage). Ainsi, la propagation des électrons est changée suivant que les deux aimantations sont parallèles ou antiparallèles c'est-à-dire que la résistance électrique de la jonction change suivant l'orientation relative des aimantations. Elle est faible lorsque les aimantations sont parallèles et forte lorsqu'elles sont antiparallèles. L'écriture d'une JTM consiste donc à changer l'orientation de l'aimantation de la couche de stockage tandis que la lecture consiste à déterminer si l'on a une forte ou une faible résistance. Les atouts de la JTM font d'elle une bonne candidate pour être une mémoire dite universelle, bien que des efforts de recherche restent à accomplir. Cependant, elle a de nombreux avantages comme la non-volatilité, la rapidité et la faible consommation à l'écriture comparée à la mémoire Flash ainsi que la résistance aux radiations. Grâce à ces avantages, on peut déjà l'utiliser dans certaines applications et en particulier dans le domaine du spatial. En effet, l'utilisation dans ce domaine permet de tirer parti de tous les avantages de la JTM en raison du fait qu'elle est intrinsèquement immune aux radiations et non-volatile. Elle permet donc de réaliser un FPGA résistant aux radiations et avec une basse consommation et de nouvelles fonctionnalités. Le travail de la thèse s'est donc déroulé sur trois ans. La première année a d'abord été dédiée à l'état de l'art afin d'apprendre le fonctionnement des JTMs, l'architecture des FPGAs, les techniques de durcissement aux radiations et de basse consommation ainsi que le fonctionnement des outils utilisés en microélectronique. Au bout de la première année, un nouveau concept d'architecture de FPGA a été proposé. Les deuxième et troisième années ont été dédiées à la réalisation de cette innovation avec la recherche de la meilleure structure de circuit et la réalisation d'un circuit de base d'un FPGA ainsi que la conception puis la fabrication d'un démonstrateur. Le démonstrateur a été testé avec succès et a permis de prouver le concept. La nouvelle architecture de circuit de FPGA a permis de montrer que l'utilisation des mémoires MRAM comme mémoire de configuration de FPGA était avantageuse et en particulier pour les technologies futures
L'anisotropie magnétique perpendiculaire induite par oxydation et recuit thermique : de la structure au magnétisme by Houmed Mohamed Garad( )

1 edition published in 2012 in French and held by 3 WorldCat member libraries worldwide

In the domain of thin film (thickness ~ Å) combining a magnetic metal (Fe, Co, Ni) and a non-magnetic (largely metal or insulator), remarkable physical properties (magnetization, transport) require fine structural characterization. In particular, include the case of tunnel junctions (metal / insulator / metal) with perpendicular magnetization which are being studied in the laboratory Spintec (UMR8191 (CEA / CNRS / UJF). These nanomaterials are deposited by physical (sputtering) in this laboratory. These nanostructures are probed by X-ray diffraction in the Neel Institute (UPR 2940) via collaboration between Spintec and a team of the Institute (Surface, Interfaces and Nanostructures Department MCFP, Condensed Matter Materials and Functions). These reflectivity measurements X are the preferred sensor of choice in the context of this thesis. Other routes are also used: using means such as synchrotron radiation absorption spectroscopy X-ray: EXAFS, XANES and XMCD. The thesis will aim to study these phenomena experimentally in continuous layers on the tunnel junction stacks with perpendicular magnetization. Specifically, the thesis will include the magnetic measurements (performed at the Institut Néel SQUID magnetometry including HALL and low temperature) through a battery of structural. This theme is part of a share in the context of work carried Spintec and dedicated to research of new materials with high added value industries (information storage on ultra-high density of discrete media for example). It registers on the other hand in strengthening links between basic research (CNRS own laboratories as Neel Institute) and applied (ECA), with strong skills in use of structural and magnetic characterization of the Institute Neel
Miniaturisation extrême de mémoires STT-MRAM : couche de stockage à anisotropie de forme perpendiculaire by Nicolas Perrissin fabert( )

1 edition published in 2018 in French and held by 3 WorldCat member libraries worldwide

Most of the actual STT-MRAM development effort is nowadays focused on out-of-plane magnetized MTJ taking advantage of the perpendicular magnetic anisotropy (PMA) arising at magnetic metal/oxide interface. This interfacial anisotropy allows conciliating large anisotropy required to insure a sufficient retention of the memory together with low switching current density thanks to weak spin-orbit coupling. However this PMA is too weak to insure 10 year retention up to 100°C in sub-20 nm devices. For deeply sub-20 nm nodes, new materials with large bulk PMA and low damping still have to be found. Furthermore, because this PMA is an interfacial effect, it is very sensitive to the structural and chemical properties of the magnetic metal/MgO interfaces contributing to dot to dot variability. To solve these problems in very small feature size STT-MRAM, we propose a totally novel approach: use MTJ stacks in which the storage layer anisotropy is uniquely controlled by its out-of-plane shape anisotropy i.e. by giving the storage layer a cylindrical shape with large enough aspect ratio (thickness / diameter typically > 1). In such structure, for purely magnetostatic reasons, the storage layer magnetization lies out-of-plane. With this approach, the geometry of conventional 2D thin layers is thus replaced by a 3D geometry. This innovative approach had several advantages: (i) it creates a strong and robust source of perpendicular anisotropy, much less sensitive to interfacial defects and thermal fluctuations; (ii) allows the use of well-known materials with mastered growth and low magnetic damping, such as Permalloy in combination with FeCoB at the interface of the MgO tunnel barrier and (iii) yields to an extreme scalability of the memory point, down to the sub-10 nm node, as the same materials can be used at very low nodes
Elaboration et étude du comportement de micro / nanoparticules antiferromagnétiques synthétiques pour applications biotechnologiques by Paul Balint( )

1 edition published in 2011 in French and held by 3 WorldCat member libraries worldwide

In the biotechnologies, the magnetic particles are more and more used in different applications, therapy or diagnostics such as: drug-delivery, cancer treatments, MRI ... This thesis, which marks the beginnings of a new research area at SPINTEC laboratory, implemented particles made by an approach top-down. The used materials are synthetic antiferromagnetic (SAF). The interest for the magnetic nanoparticles was shown in the introduction. The study made at SPINTEC was first of all the characterization and modeling of different SAF materials, and the development of the technological processes for making the particles. Then the work was devoted to observation and modeling of the behavior of the particles in suspension in the applied magnetic field. A model of self-bias and agglomeration of SAF particles allowed to determine a susceptibility threshold below which the particles remain dispersed in solution, avoiding the agglomeration phenomena
Réduction du champ d'écriture de mémoires magnétiques à écriture assistée thermiquement à l'aide du couple de transfert de spin by Antoine Chavent( )

1 edition published in 2016 in French and held by 3 WorldCat member libraries worldwide

Spintronics offers new solutions in microelectronics regarding architecture, to solve scaling and consumption issues. Its main product, magnetic random access memories (MRAM), is composed of magnetic tunnel junctions (MTJ). Switching of the magnetic moment storing the data is facilitated by a thermally assisted writing method developed by Crocus Technology. The storage layer's magnetization is coupled to an antiferromagnetic layer to stabilize it (pinned layer). Joule heating thanks to a tunneling current allows freeing the storage layer to write information thanks to a magnetic field. Generating a magnetic field still consumes power. To solve this issue, the idea explored in the thesis is to harness advantageously the spin transfer torque arising from the heating current in order to lower the writing field by changing the heating current polarity depending on the state to write. To do this, 1 kbit test vehicles have been tested, for which it is shown that spin transfer torque influence allows reducing the writing field. A new structure has been developed, consisting of a pinned synthetic ferrimagnetic (SyF) storage layer, to get benefits from the spin transfer torque without degrading epitaxial relations necessary to have a good stability and a good signal. To study the influence of spin transfer torque in details, field-voltage phase diagrams have been measured for various structures, by separating the elementary parts of the full structure. Apart from the expected spin transfer torque, an even effect of the current has been observed, favoring the antiparallel state whatever the current polarity. This effect can be found both in pinned layers and free layers, and can be explained thanks to perpendicular spin transfer torque as suggested by the shape of the diagrams obtained on free layers. Besides, writing diagrams of SyF storage layer have a complexe shape that may be related to the excitation of one only layer of the two of the SyF by spin transfer torque. By varying the resistance-area product (RA) of the MTJ, we showed that spin transfer torque seems to keep its proportionality to current density for structures with pinned storage layer. Another side of the work is related to the cooling phase at the end of the thermally assisted writing. Influence of the cooling rate on the efficiency of spin transfer torque was evidenced, and it is showed that a gradual decrease of the voltage let reach a quasistatic cooling regime in which the writing error rate is reduced by one order of magnitude on some structures. The different results are linked to the temperature dependence of RKKY coupling inside the SyF. This allows estimating real time change of temperature. Finally, thermoelectric effect due to heating asymmetry is studied
Etude de fiabilité des jonctions tunnel magnétiques pour applications à forte densité de courant by Selma Amara( )

1 edition published in 2012 in French and held by 3 WorldCat member libraries worldwide

The thesis objective is to study the Magnetic Tunnel Junction reliability and cyclability to more understand the barrier breakdown mechanisms. An investigation of barrier endurance till electrical breakdown in MgO-based magnetic tunnel junctions (MTJs) is presented. Samples were tested under pulsed electrical stress. By studying the effect of delay between successive pulses, an optimum endurance of MTJs is observed for an intermediate value of delay between pulses corresponding to an optimum trade-off between the average density of charge trapped in the barrier and the amplitude of its time-modulation at each voltage pulse. Furthermore, a charge trapping/detrapping model was developed which support this interpretation. The study emphasizes the role of electron trapping/detrapping mechanisms on the tunnel barrier reliability. It also shows that extremely long endurance could be obtained in MTJs by reducing the density of electron trapping sites in the tunnel barrier. Then the write endurance and the 1/f noise of electrical origin were characterized in CoFeB/MgO/CoFeB MTJ for STT-MRAM or TA-MRAM. A correlation was observed and explained by the presence of electron trapping sites in the MgO barrier and the role of electron trapping/detrapping phenomena in both the MTJ reliability and its 1/f electrical noise power. These results suggest that 1/f noise could be used as a predictive characterization of the MTJ endurance. Finally, as thesis perspectives, some complement measurements were proposed to further investigate this model and an optimization of MgO barrier which could be carried out to reduce the density of these trapping sites was presented to ameliorate the MTJs reliability
Spin electronics( Book )

1 edition published in 2007 in English and held by 3 WorldCat member libraries worldwide

Elaboration de micro/nanopinces magnétiques pour applications biotechnologiques by Cécile Iss( )

1 edition published in 2015 in English and held by 3 WorldCat member libraries worldwide

Cette thèse propose de réaliser des micro/nano-pinces magnétiques articulées dont l'actionnement à distance est obtenu par l'application d'un champ magnétique. Cette idée innovante consiste à relier par l'un de leurs côtés deux microparticules magnétiques parallélépipédiques à l'aide d'une nano-charnière en or flexible. Destinées à des applications biotechnologiques et médicales, ces pinces ont pour finalité de capturer des micro/nano-objets ciblés biochimiquement pour y appliquer et mesurer des forces. Le défi de ce projet était de mener, à partir d'une idée simple, un ensemble d'études à la fois théoriques et technologiques, pour aboutir à une première preuve de concept. Dans ce but, un modèle analytique a d'abord été construit pour prédire le comportement magnéto-mécanique des pinces en fonction de divers paramètres physiques. Ensuite, un procédé de fabrication inspiré des techniques de la microélectronique a été développé pour parvenir à la réalisation d'un prototype de pince fonctionnel. Enfin, l'ouverture par l'action d'un champ magnétique de pinces fixées à un substrat, a pu être démontrée à l'aide d'une expérience originale installée dans un microscope électronique à balayage. Les résultats de ces expériences, en bon accord avec nos prédictions théoriques, ont permis de quantifier le comportement mécanique de la nano-charnière en or. Fixées à un substrat, ces pinces forment un réseau de micro-surfaces réfléchissantes qui trouveront des applications en microfluidique (bio-puces) ou en nano-physique. Libérées en solution, les pinces pourraient être employées de manière originale en micro-manipulation d'objets biologiques ou diagnostic et thérapie cellulaire
Spin electronics( Book )

5 editions published in 2007 in English and held by 3 WorldCat member libraries worldwide

Scalabilité et amélioration des propriétés de couplage d'échange pour TA-MRAM by Giovanni Maria Vinai( )

1 edition published in 2013 in English and held by 3 WorldCat member libraries worldwide

Le couplage d'échange entre une couche ferromagnétique (F) et une couche antiferromagnétique (AF) permet de piéger l'aimantation de la couche ferromagnétique. Ce phénomène est largement utilisé dans des systèmes magnétiques complexes, telles que les vannes de spins, ou les mémoires MRAM, où il permet de constituer des couches de références, normalement insensibles aux cycles d'écriture des couches de stockage. On remarque aux petites dimensions, lorsque la taille des cellules diminue en dessous de la centaine de nm, des renversements partiels ou complets des électrodes de référence, dus à un basculement du réseau de spins dans l'AF. L'objectif de cette thèse est de comprendre ces phénomènes de renversement, de les quantifier en fonction de la dimension latérale des dispositifs, et de présenter des solutions viables afin d'accroître la stabilité des systèmes de stockage. Ce travail essentiellement expérimental, comprenant dépôts, lithogravure et caractérisations, se déroulera pour la majeure partie au sein du laboratoire SPINTEC (UMR8191). L'étudiant sera cependant amené à collaborer avec plusieurs entités du pôle grenoblois, notamment pour les mesures magnéto-optiques, les analyses cristallographiques, ainsi que pour une partie de simulation atomistique ; il devra aussi s'intéresser à l'intégration industrielle de ses études en rendant compte de ses résultats, en les discutant, afin que Crocus Technology en bénéficie directement. La thèse, se déroulant sur trois ans, explorera les points suivants : i) Etude de la stabilité thermique en fonction de la taille des motifs (0-15mois) L'étudiant déposera par pulvérisation cathodique des bicouches F/AF (AF=FeMn, PtMn ou IrMn) qui seront gravées sur la plate forme de technologie amont (PTA) localisée sur le site du CEA/Grenoble. Il caractérisera par des mesures d'effet kerr ou de magnétotransport les propriétés magnétiques des bicouches, notamment les distributions de TB, de champ d'échange, en fonction de la taille des motifs. Il participera aux analyses cristallographiques en collaboration avec le Service général des rayons X et le laboratoires d'Etude des Matériaux par Microscopie Avancée (LEMMA) (du CEA/Grenoble/INAC/SP2M). Ces analyses qui donneront des renseignements sur les tailles de grains et leur distribution seront utilisées pour comprendre les mesures magnétiques dans un premier temps, et seront un point de départ pour optimiser via des recuits, ou l'ajout d'éléments d'addition, la stabilité des systèmes aux dimensions réduites, typiquement <100nm. ii) Etude du couplage inter-grain dans l'AF (15-22mois) L'étudiant réalisera des mesures de trainage magnétique et déterminera les volumes de nucléation dans l'AF et les comparera aux données cristallographiques. Il essaiera de déterminer l'importance de ce couplage dans la stabilité des points mémoire en jouant sur son intensité (recuits, éléments d'addition...), ceci participant de l'optimisation de l'anisotropie d'échange aux petites dimensions présentée dans la partie précédente. iii) Volet de simulations atomistiques (22-30mois) L'étudiant collaborera avec le laboratoire LSIM et notamment F. Lançon afin de simuler, grâce à un code de calcul développé localement, l'impact de la cristallographie (taille de grains, couplage inter-grains, désordre interfacial et rugosité) sur les propriétés de l'anisotropie d'échange dans les systèmes F/AF de taille réduite. Ces simulations permettront de comprendre les mesures expérimentales réalisées en parallèle et d'ouvrir de nouvelles voies exploratoires pour optimiser les valeurs de champ d'échange en vue de leur intégration dans les dispositifs
Mastering the influence of thermal fluctuations on the magnetization switching dynamics of spintronic devices by Bertrand Lacoste( )

1 edition published in 2013 in English and held by 3 WorldCat member libraries worldwide

Spin-transfer torque magnetic random-access memory (STTRAM) are very promising non-volatile and enduring memories to replace charged-based RAM. However, in conventional in-plane or out-of-plane STTRAM technologies, the switching time is limited to about 10~ns because the reversal process is stochastic i.e. it is triggered by thermal fluctuations. In order to render the reversal deterministic and faster, an approach consists in adding to the magnetic tunnel junction (MTJ) stack another spin-polarizing layer whose magnetization is orthogonal to that of the MTJ reference layer. We particularly investigated the case where a perpendicular polarizer is added to an in-plane magnetized tunnel junction. The STT from the perpendicular polarizer initiates the reversal, but it also creates oscillations of the resistance between its two extremal values. This behavior is usually interesting to realize STT nano-oscillators (STO). In this thesis, the dynamics of the system comprising an in-plane free layer, an in-plane reference layer and a perpendicular polarizer is studied both experimentally and theoretically (analytically and by simulations) in the framework of the macrospin approximation. For a single layer free layer oscillating due to the STT of the perpendicular polarizer, an accurate description of the oscillations is presented, in which the anisotropy field, the applied field and the in-plane STT are treated as perturbations. In the particular case of a synthetic ferrimagnetic (SyF) free layer, analytical expressions of the critical currents and of the oscillations equation of motion are computed and compared to simulations. These results are used to determine the phase diagram of the complete system. The in-plane anisotropy field is found to play a dramatic role, which is confirmed by experimental data from real-time measurements on MgO-based nano-pillars. It is shown that the cell aspect ratio can be used to tune the relative influence of the STT from the in-plane reference layer and from the out-of-plane polarizer. This allows achieving well controlled sub-nanosecond switching in STTRAM
Jonctions tunnel magnétiques à anisotropie perpendiculaire et écriture assistée thermiquement by Sébastien Bandiera( )

1 edition published in 2011 in French and held by 3 WorldCat member libraries worldwide

In order to increase the storage density of magnetoresistive random access memories (MRAM), magnetic materials with perpendicular anisotropy are very appealing thanks to high anisotropy. However, the enhancement of anisotropy induces an increase of writing consumption as well. A new thermally assisted switching concept has been proposed by SPINTEC laboratory. The principle is to design a highly stable structure at stand-by temperature which loses its anisotropy when heated, making thus the switching easier. The aim of this thesis is to validate experimentally this concept. The first chapters describe the optimisation of out-of-plane magnetic materials such as (Co/Pt), (Co/Pd) and (Co/Tb) multilayers. Their integration in magnetic tunnel junctions is then presented. The evolution of anisotropy with temperature is a critical parameter for thermally assisted writing and has been therefore studied. Finally, the efficiency of this thermally assisted writing is demonstrated: the developed structures present a reduced consumption compared to standard structures and high stability at room temperature
Développement de cellules mémoires magnétiques à accès aléatoire (MRAM) auto-référencées assistées thermiquement by Quentin Stainer( )

1 edition published in 2014 in English and held by 3 WorldCat member libraries worldwide

The goal of this thesis was to model and demonstrate experimentally the read and write functionalities of a new thermally assisted magnetic random access memory structure, the self-referenced MRAM. The self-referenced MRAM stack is obtained from the thermally assisted MRAM one by removing the reference antiferromagnetic, effectively replacing the pinned reference layer by a free layer: the sense layer. By remotely switching the sense layer magnetization, by means of an external field, the storage layer magnetization direction, and as such the stored bit state, can be probed in-situ. Due the possibility to program both magnetic layers individually, self-referenced MRAM can be operated as a Magnetic Logic Unit, combining in-stack the storage and exclusive-or logic functions and thereby opening new application ranges. The read and write functionality of self-referenced MRAM were experimentally demonstrated on a first batch of samples. However, the field requirements were found to be higher than the target requirements for fully functional industrial products. In order to optimize the read and write field requirements, we developed a macrospin model based on the Stoner-Wohlfarth model of magnetization reversal. By introducing magnetostatic, RKKY and ferromagnet/antiferromagnet exchange coupling phenomena, we calculated a general form of the energy for any type of MRAM magnetic stack. A previously proposed highly efficient switching mode, relying on the magnetostatic interactions between the sense and the storage layer, was effectively predicted by the model and experimentally demonstrated in new samples. An excellent agreement was obtained between the model and the experimental results. Increasing the stiffness of the storage layer was found to be critical in order to minimize the read field requirements at decreasing patterning dimensions. Material developments were performed to maximize the RKKY coupling in the synthetic ferrimagnet storage layer. In order to study the reproducibility of the write operation, the influence of thermal activation was modelled by calculating energy barriers and transition paths and compared with on-the-fly measurements of switching probabilities on the new set of samples with a stiffer storage layer. Again, an excellent agreement was obtained between the model and the experiments. Based on the model developed, we built a roadmap describing the magnetic stack to use, that allows a downscaling of the self-referenced MRAM down to 45 nm while conserving manageable field requirements. Due to fundamental limitations in field-induced switching MRAM technology, reaching higher densities was found to require increasing the individual storage capacity of each MTJ, i.e. storing multiple bits per unit cell. A new angle-based storage method taking advantage of the sense layer free magnetization was investigated. Using the magnetic model developed previously, suitable samples were designed and allowed to experimentally demonstrate up to 4 bits per single MTJ. The field requirements were however found to be substantially higher than those compatible with a fully functional product. A new write method, predicted by the model, was investigated and exploited in the building of a second roadmap down to 45 nm. Mirrored dual barrier structures were then studied, with the experimental demonstration of their manufacturability and functionality. Notably, a highly efficient write mechanism similar to that observed in single barrier self-referenced MRAM was obtained. Finally, the adaptation of angle-based storage to these dual barrier devices was modeled, leading to the proposition of a method to store up to 8 bits per single cell
 
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Audience level: 0.42 (from 0.02 for Magnétism ... to 0.96 for Réduction ...)

Alternative Names
Dieny, Bernard

Languages
English (18)

French (16)