Spelling suggestions: "subject:"giant magnetoresistance"" "subject:"giant magnetoresistances""
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Side Channel Analysis of a Java-based Contactless Smart CardMateos Santillan, Edgar January 2012 (has links)
Smart cards are widely used in different areas of modern life including identification, banking, and transportation cards. Some types of cards are able to store data and process information as well. A number of them can run cryptographic algorithms to enhance the security of their transactions and it is usually believed that the information and values stored in them are completely safe. However, this is generally not the case due to the threat of the side channel. Side channel analysis is the process of obtaining additional information from the internal activity of a physical device beyond that allowed by its specifications. There exist different techniques to attempt to obtain information from a cryptosystem using other ways than the normally permitted. This thesis presents a series of experiments intended to study the side channel from a particular type of smart card, known as Java Cards. This investigation uses the well known technique, Correlation Analysis, and a new type of side channel attack called fast correlation in the frequency domain to study the side channel of Java Cards. This research presents a giant magnetoresistor (GMR) probe and for the first time, this type of sensor is used to investigate the side channel. A novel setup designed for studying the side channel of smart cards is described and two metrics used to evaluate the analysis results are presented. After testing the GMR probe and methodology on electronic devices executing the Advanced Encryption Standard (AES), such as 8 bit microcontrollers and 128 bit AES implementations on FPGAs, these techniques were applied to analyse two different models of Java Cards working in the contactless mode. The results show that successful attacks on a software implementation of AES running on both models of Java Cards are possible.
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Magneto-transport Study of 3D Topological Insulator Bi2Te3 And GaAs/AlGaAs 2D Electron SystemWang, Zhuo 08 August 2017 (has links)
Magneto-transport study on high mobility electron systems in both 2D- and 3D- case has attracted intense attention in past decades. This thesis focuses on the magnetoresistance behavior in 3D topological insulator Bi2Te3 and GaAs/AlGaAs 2D electron system at low magnetic field range 0.4T the first drop at T~3.4K to tndium superconductor and considered the second drop at lower temperature as the proximity effect that occurred near the interface between these two materials. On the other hand, GaAs/AlGaAs heterostructure, as a III-V semiconductor family, has been extensively studied for exploring many interesting phenomena due to the extremely high electron mobility up to 10^7 cm^2/Vs. In this thesis, two interesting phenomena are present and discussed in a GaAs/AlGaAs system, which are the electron heating induced tunable giant magnetoresistance study and phase inversion in Shubnikov-de Haas oscillation study, respectively. By applying elevated supplementary dc current bias, we found a tunable giant magnetoresistance phenomenon which is progressively changed from positive to giant negative magnetoresistance. The observed giant magnetoresistance is successfully simulated with a two-term Drude model at all different dc biases, I_{dc}, and temperature, T. In addition, as increasing the dc current bias, a phase inversion behavior was observed in Shubnikov-de Haas oscillation, which was further demonstrated by the simulation with an exponential damped cosine function. This thesis also presents an ongoing project, which is the observation and fabrication of 2D layered materials. The studied 2D layered materials includes graphene, biron nitride, Molybdenum disulfide, etc. At the end, a future work about fabrication of the 2D layered materials devices as well as the suggestion about the measurement are discussed.
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Solid State Chemistry Of Transition Metal Oxides With Fascinating PropertiesMahesh, R 02 1900 (has links) (PDF)
No description available.
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Magnetoresistance in Permalloy/GaMnAs Circular MicrostructuresGuenther, Justin 15 August 2014 (has links)
No description available.
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Integrated Micro-Origami SensoricsBecker, Christian 16 May 2024 (has links)
This work presents the successful development of micro-origami sensorics by 3D self-assembling and reconfiguring in space integrated thin-film magnetic sensors, which rely on anisotropic (AMR) and giant magnetoresistance (GMR). Stimuli responsive polymeric materials able to reshape into mesoscale 3D “Swiss-roll” and polygonal architectures accomplish a strain driven parallel spatial realignment of magnetic sensors from the in-plane state. High performance 3D magnetic vector angular encoders demonstrates the successful realization of complex sensor configurations. The proposed concepts rely on parallel wafer scale processes, which allow for a monolithic fabrication of 3D sensor arrays and pave the way towards active sensory matrix circuits.
As a proof of this concept, magneto-resistive Wheatstone bridge sensors are developed and integrated in the self-assembling platform at predefined rigid regions and integrated with an active matrix backplane circuit. This circuit, based on a-IGZO TFT technology, is specially designed for the operation with the Wheatstone bridge differential sensors and optimized to be compatible with the micro-origami self-folding technology. Such an active sensory matrix system with integrated 3D self-assembled pixels is called Integrated Micro-Origami Sensors or in short IMOS. IMOS is capable for static and dynamic mapping of magnetic fields enabling spatiotemporal mapping of artificial magnetic hair arrays embedded in an elastic skin layer. The presented results offer a fresh strategy for large area integration of microscale 3D electronic devices with various vector functionalities in active matrix circuits, which are of great interest in novel robotics, bioelectronics and diagnostic systems.
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Charge Transport in Nano-Constrictions and Magnetic MicrostructuresTolley, Robert Douglas 10 August 2012 (has links)
No description available.
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Stretchable Magnetoelectronics / Dehnbare MagnetoelektronikMelzer, Michael 22 December 2015 (has links) (PDF)
In this work, stretchable magnetic sensorics is successfully established by combining metallic thin films revealing a giant magnetoresistance effect with elastomeric materials. Stretchability of the magnetic nanomembranes is achieved by specific morphologic features (e.g. wrinkles), which accommodate the applied tensile deformation while maintaining the electrical and magnetic integrity of the sensor device. The entire development, from the demonstration of the world-wide first elastically stretchable magnetic sensor to the realization of a technology platform for robust, ready-to-use elastic magnetoelectronics with fully strain invariant properties, is described. The prepared soft giant magnetoresistive devices exhibit the same sensing performance as on conventional rigid supports, but can be stretched uniaxially or biaxially reaching strains of up to 270% and endure over 1,000 stretching cycles without fatigue. The comprehensive magnetoelectrical characterization upon tensile deformation is correlated with in-depth structural investigations of the sensor morphology transitions during stretching.
With their unique mechanical properties, the elastic magnetoresistive sensor elements readily conform to ubiquitous objects of arbitrary shapes including the human skin. This feature leads electronic skin systems beyond imitating the characteristics of its natural archetype and extends their cognition to static and dynamic magnetic fields that by no means can be perceived by human beings naturally. Various application fields of stretchable magnetoelectronics are proposed and realized throughout this work. The developed sensor platform can equip soft electronic systems with navigation, orientation, motion tracking and touchless control capabilities. A variety of novel technologies, like smart textiles, soft robotics and actuators, active medical implants and soft consumer electronics will benefit from these new magnetic functionalities.
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Beiträge zur Theorie des Supermagnetwiderstandes in magnetischen VielfachschichtenZahn, Peter 11 August 2021 (has links)
Es werden ab-initio Rechnungen des Supermagnetwiderstands-Effektes von Fe/Cr-Multilagen vorgestellt. Die Elektronenstruktur wurde im Rahmen einer LCAO-Superzellen-Rechnung bestimmt. Als Störung der idealen Schichtstruktur wurden Cr-Defekte in Fe angenommen, die durch spinabhängige Relaxationszeiten beschrieben werden. Die elektrischen Transportkoeffizienten wurden durch Lösung der linearisierten Boltzmann-Gleichung in Relaxationszeitnäherung unter Verwendung des Mott-schen Zweistrommodells berechnet. Bei den betrachteten Systemen variierte die Dicke der Fe-Schicht zwischen 3 und 9 Monolagen, die der Cr-Schicht zwischen 1 und 13 Monolagen. In Abhängigkeit von der Fe- bzw. Cr-Schichtdicke ergeben sich in Übereinstimmung mit den Experimenten charakteristische Oszillationen des Supermagnetwiderstandes. Es wird der Einfluß der Spinanisotropie der Streuung auf den Effekt untersucht. Insbesondere kann gezeigt werden, daß der Effekt auch für spinunabhängige Streuung existiert. / Ab-initio calculations of the Giant Magnetoresistance (GMR) for Fe/Cr multilayers are presented. The electronic structure of the Fe/Cr superlattice is calculated within an optimized LCAO scheme using the local spin density approximation. The scattering of the electrons by Cr impurities in an Fe environment is taken into account by spin dependent relaxation times. The transport is described quasiclassically by solving the linearized Boltzmann equation in relaxation time approximation. In agreement with experiments characteristic oscillations of the GMR are obtained in dependence on the Cr and Fe layer thickness. It can be shown, that the GMR can be reduced or increased by the spin anisotropy of the scattering, but the phenomenon still exists for spin-independent scattering.
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Magnetic and Magneto-Transport Properties of Hard Magnetic Thin Film Systems / Magnetische und magnetoresistive Eigenschaften von hartmagnetischen DünnschichtsystemenMatthes, Patrick 21 March 2016 (has links) (PDF)
The present thesis is about the investigation of ferromagnetic thin film systems with respect to exchange coupling, magnetization reversal behavior and effects appearing in magnetic heterostructures, namely the exchange bias and the giant magnetoresistance effect. For this purpose, DC magnetron sputtered thin films and multilayers with perpendicular magnetic anisotropy were prepared on single crystalline and rigid as well as flexible amorphous substrates.
The first part concentrates on magnetic data storage applications based on the combination of the concept of bit patterned media and three dimensional magnetic memory, consisting of at least two exchange decoupled ferromagnetic storage layers. Here, [Co/Pt] multilayers, revealing different magnetic anisotropies, have been applied as storage layers and as spacer material Pt and Ru was employed. By the characterization of the magnetization reversal behavior the exchange coupling in dependence of the spacer layer thickness was studied. Furthermore, with regard to the concept of bit patterned media, the layers were also grown on self-assembled silica particles, leading to an exchange decoupled single-domain magnetic dot array, which was studied by magnetic force microscope imaging and angular dependent magneto-optic Kerr effect magnetometry to evaluate the reversal mechanism and its dependence on the array dimensions, mainly the diameter of the silica particles and layer thicknesses. To complete the study, micromagnetic simulations were performed to access smaller dimensions and to investigate the dependence of intralayer as well as interlayer coupling on the magnetization reversal of the dot array with multiple storage layers.
The second part focuses on the investigation of the giant magnetoresistance effect in systems with perpendicular magnetic anisotropy, where L10 -chemically ordered FePt alloys and [Co/Pt] as well as [Co/Pd] multilayers were utilized. In case of FePt, where high temperatures during the deposition are necessary to induce the chemical ordering, diffusion and alloying of the spacer material often prevent a sufficient exchange decoupling of the ferromagnetic layers. However, with Ru as spacer material a giant magnetoresistance effect could be achieved. Large improvements of the magnetoresistive behavior of such trilayer structures are presented for [Co/Pt] and [Co/Pd] multilayers, which can be deposited at room temperature not limiting the choice of spacer as well as substrate material. Furthermore, in systems consisting of one ferromagnet with perpendicular magnetic anisotropy and one ferromagnet with in-plane magnetic easy axis, a linear and almost hysteresis-free field dependence of the electrical resistance was observed and the behavior for various thickness series has been intensively studied. Finally, the corrosion resistance in dependence of the capping layer material as well as the magnetoresistance of a strained flexible pseudo-spin-valve structure is presented.
In addition, in chapter 2.5.2 an experimental study of an improved crystal growth of FePt at comparable low temperatures by molecular beam epitaxy and further promoted by a surfactant mediated growth using Sb is shown. Auger electron spectroscopy as well as Rutherford backscattering spectrometry were carried out to confirm the surface segregation of Sb and magnetic characterization revealed an increase of magnetic anisotropy in comparison to reference layers without Sb. / Die vorliegende Dissertation beschäftigt sich mit der Untersuchung ferromagnetischer Dünnschichtsysteme im Hinblick auf die Austauchkopplung, das Ummagnetisierungsverhalten und Effekte wie z.B. den Exchange Bias Effekt oder den Riesenmagnetwiderstandseffekt (GMR), welche in derartigen Heterostrukturen auftreten können. Die Probenpräparation erfolgte mittels DC Magnetronsputtern, wobei auf einkristallinen aber auch flexiblen sowie starren amorphen Substraten abgeschieden wurde.
Im ersten Teil der Arbeit werden Untersuchungen mit dem Hintergrund einer Anwendung als magnetischer Datenträger vorgestellt. Konkret werden hier die Konzepte Bit Patterned Media (BPM) und 3D Speicher miteinander kombiniert. Letzteres Konzept basiert auf der Verwendung wenigstens zweier austauschentkoppelter ferromagnetischer Schichten, für welche [Co/Pt] Multilagen mit unterschiedlicher magnetischer Anisotropie verwendet wurden. Als Zwischenschichtmaterial diente Pt und Ru. Durch die Charakterisierung des Ummagnetisierungsverhaltens wurde die Austauschkopplung in Abhängigkeit der Zwischenschichtdicke untersucht. Darüber hinaus wurden jene Schichtstapel zur Realisierung des BPM-Konzeptes auf selbstangeordnete SiO2 Partikel mit unterschiedlichen Durchmessern aufgebracht, durch welche sich lateral austauschentkoppelte, eindomänige magnetische Nanostrukturen erzeugen lassen. Zur Untersuchung des Ummagnetisierungsverhaltens und der jeweiligen Größenabhängigkeiten (maßgeblich Durchmesser und Schichtdicke) wurden diese mittels Magnetkraftmikroskopie sowie winkelabhängiger magnetooptischer Kerr Effekt Magnetometrie untersucht. Zur weiteren Vertiefung des Verständnisses noch kleinerer Strukturgrößen erfolgten mikromagnetische Simulationen, bei denen die magnetischen Wechselwirkungen lateral (benachbarte 3D Elemente) als auch vertikal (Wechselwirkungen ferromagnetischer Schichten innerhalb eines 3D Elementes) im Interesse standen, sowie deren Auswirkungen auf das Ummagnetisierungsverhalten des gesamten Feldes.
Der Fokus des zweiten Teils liegt auf der Untersuchung des Riesenmagnetwiderstandseffektes in Systemen mit senkrechter Sensitivität. Dafür sind ferromagnetische Schichten mit senkrechter magnetischer Anisotropie nötig, wobei hier die chemisch geordnete L10-Phase der FePt Legierung und [Co/Pt] sowie [Co/Pd] Multilagen Anwendung fanden. Für eine chemische Ordnung der FePt Legierung sind hohe Temperaturen während der Schichtabscheidung notwendig, welche eine hinreichende Austauschentkopplung beider ferromagnetischer Schichten meist nicht gewährleisten. Grund dafür sind einsetzende Diffusionsprozesse als auch Legierungsbildungen mit dem Zwischenschichtmaterial. In der vorliegenden Arbeit konnte der GMR Effekt daher ausschließlich mit einer Ru Zwischenschicht in FePt basierten Trilagensystemen nachgewiesen und charakterisiert werden. Enorme Verbesserungen der magnetoresistiven Eigenschaften werden im Anschluss für [Co/Pt] und vor allem [Co/Pd] Multilagen vorgestellt. Diese Schichtsysteme mit senkrechter magnetischer Anisotropie können bei Raumtemperatur präpariert werden und stellen daher keine weiteren Anforderungen an das Zwischenschichtmaterial sowie die verwendeten Substrate. Hier wurden neben Systemen mit ausschließlich senkrechter magnetischer Anisotropie auch Systeme mit gekreuzten magnetischen Anisotropien intensiv untersucht, da diese durch einen linearen und weitgehend hysteresefreien R(H) Verlauf imHinblick auf Sensoranwendungen enorme Vorteile bieten. Letztendlich wurde die Korrosionsbeständigkeit in Abhängigkeit des Deckschichtmaterials als auch die mechanische Belastbarkeit von auf flexiblen Substraten abgeschiedenen GMR-Schichtstapeln untersucht.
Zusätzlich wird in Kapitel 2.5.2 eine experimentelle Studie zum Surfactant-gesteuerten Wachstum der FePt Legierung mittels Molekularstrahlepitaxie vorgestellt. Als Surfactant dient Sb, wodurch die Kristallinität bei geringer Depositionstemperatur deutlich verbessert werden konnte. Die Oberflächensegregation von Sb wurde mittels Auger Elektronenspektroskopie und Rutherford Rückstreuspektrometrie verifiziert und die Charakterisierung magnetischer Eigenschaften belegt einen Anstieg der magnetischen Anisotropieenergie im Vergleich zu Referenzproben ohne Sb.
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Stretchable MagnetoelectronicsMelzer, Michael 19 November 2015 (has links)
In this work, stretchable magnetic sensorics is successfully established by combining metallic thin films revealing a giant magnetoresistance effect with elastomeric materials. Stretchability of the magnetic nanomembranes is achieved by specific morphologic features (e.g. wrinkles), which accommodate the applied tensile deformation while maintaining the electrical and magnetic integrity of the sensor device. The entire development, from the demonstration of the world-wide first elastically stretchable magnetic sensor to the realization of a technology platform for robust, ready-to-use elastic magnetoelectronics with fully strain invariant properties, is described. The prepared soft giant magnetoresistive devices exhibit the same sensing performance as on conventional rigid supports, but can be stretched uniaxially or biaxially reaching strains of up to 270% and endure over 1,000 stretching cycles without fatigue. The comprehensive magnetoelectrical characterization upon tensile deformation is correlated with in-depth structural investigations of the sensor morphology transitions during stretching.
With their unique mechanical properties, the elastic magnetoresistive sensor elements readily conform to ubiquitous objects of arbitrary shapes including the human skin. This feature leads electronic skin systems beyond imitating the characteristics of its natural archetype and extends their cognition to static and dynamic magnetic fields that by no means can be perceived by human beings naturally. Various application fields of stretchable magnetoelectronics are proposed and realized throughout this work. The developed sensor platform can equip soft electronic systems with navigation, orientation, motion tracking and touchless control capabilities. A variety of novel technologies, like smart textiles, soft robotics and actuators, active medical implants and soft consumer electronics will benefit from these new magnetic functionalities.:Outline
List of abbreviations 7
1. INTRODUCTION
1.1 Motivation and scope of this work 8
1.1.1 A brief review on stretchable electronics 8
1.1.2 Stretchable magnetic sensorics 10
1.2 Technological approach 11
1.3 State-of-the-art 12
2. THEORETICAL BACKGROUND
2.1 Magnetic coupling phenomena in layered structures 14
2.1.1 Magnetic interlayer exchange coupling 14
2.1.2 Exchange bias 15
2.1.3 Orange peel coupling 16
2.2 Giant magnetoresistance 17
2.2.1 Electronic transport through ferromagnets 17
2.2.2 The GMR effect 19
2.2.3 GMR multilayers 20
2.2.4 Spin valves 21
2.3 Theory of elasticity 22
2.3.1 Elastomeric materials 22
2.3.2 Stress and strain 23
2.3.3 Rubber elasticity 25
2.3.4 The Poisson effect 26
2.3.5 Viscoelasticity 27
2.3.6 Bending strain in a stiff film on a flexible support 27
2.4 Approaches to stretchable electronic systems 28
2.4.1 Microcrack formation 28
2.4.2 Meanders and compliant patterns 29
2.4.3 Surface wrinkling 30
2.4.4 Rigid islands 32
3. METHODS & MATERIALS
3.1 Sample fabrication 34
3.1.1 Polydimethylsiloxane (PDMS) 34
3.1.2 PDMS film preparation 35
3.1.3 Lithographic structuring on the PDMS surface. 36
3.1.4 Magnetic thin film deposition 38
3.1.5 GMR layer stacks 40
3.1.6 Mechanically induced pre-strain 43
3.1.7 Methods and materials for the direct transfer of GMR sensors 45
3.1.8 Materials used for imperceptible GMR sensors 47
3.2 Characterization 48
3.2.1 GMR characterization setup with in situ stretching capability 48
3.2.2 Sample mounting 50
3.2.3 Electrical contacting of stretchable sensor devices 51
3.2.4 Customized demonstrator electronics 52
3.2.5 Microscopic investigation techniques 53
4. RESULTS & DISCUSSION
4.1 GMR multilayer structures on PDMS 54
4.1.1 Pre-characterization 54
4.1.2 Thermally induced wrinkling 55
4.1.3 Self-healing effect 57
4.1.4 Demonstrator: Magnetic detection on a curved surface 60
4.1.5 Sensitivity enhancement 61
4.1.6 GMR sensors in circumferential geometry 64
4.1.7 Stretchability test 67
4.2 Stretchable spin valves 69
4.2.1 Random wrinkles and periodic fracture 70
4.2.2 GMR characterization 73
4.2.3 Stretching of spin valves 74
4.2.4 Microcrack formation mechanism 76
4.3 Direct transfer printing of GMR sensorics 81
4.3.1 The direct transfer printing process 82
4.3.2 Direct transfer of GMR microsensor arrays 84
4.3.3 Direct transfer of compliant meander shaped GMR sensors 86
4.4 Imperceptible magnetoelectronics 89
4.4.1 GMR multilayers on ultra-thin PET membranes 89
4.4.2 Imperceptible GMR sensor skin 92
4.4.3 Demonstrator: Fingertip magnetic proximity sensor 93
4.4.4 Ultra-stretchable GMR sensors 94
4.4.5 Biaxial stretchability 99
4.4.6 Demonstrator: Dynamic detection of diaphragm inflation 101
5. CONCLUSIONS & OUTLOOK
5.1 Achievements 102
5.2 Outlook 104
5.2.1 Further development steps 104
5.2.2 Prospective applications. 105
5.3 Technological impact: flexible Bi Hall sensorics 106
5.3.1 Application potential 106
5.3.2 Thin and flexible Hall probes 107
5.3.3 Continuative works and improvements 108
5.4 Activities on technology transfer and public relations 108
Appendix
References 110
Selbständigkeitserklärung 119
Acknowledgements 120
Curriculum Vitae 121
Scientific publications, contributions, patents, grants & prizes 122
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