The physics of ultracold atomic gases has been the subject of a long standing theoretical and experimental research over the last half century. The development of evaporative cooling techniques and the realization of the first Bose-Einstein Condensate (BEC) in 1995 gave a great advantage to the field. A great experimental knowledge of the fundamental properties of BECs, such as long-range coherence, superfluidity and topological excitations, has now been acquired. On top of these advances, current research on ultracold atoms is also focusing on quantum simulations, which aim at building analogue models of otherwise difficult to compute physical systems in the lab. In this context, BECs, with their enhanced coherence, many-body dynamics and superfluid character offer a powerful platform for advances in the field. Shortly after the first realization of a BEC, research started also investigating the physics of quantum mixtures of a BECs, either composed of different atomic species or isotopes, or of atoms occupying different hyperfine states. The latter are known as spin mixtures, or spinor condensates. The presence of multiple components interacting through mutual contact interactions enriches the physics of the condensate, introducing ground states with magnetic ordering as well as spin dynamics, which can be order of magnitudes less energetic than the density one. On top of this, hyperfine states can be coherently coupled with an external resonant radiation. Interesting physics arises when the strength of the coupling is comparable with the energy of spin excitations, an example of which is given by the emergence of the internal Josephson effect. This regime has been the subject of intense theoretical studies in the past twenty years, however its experimental realization on ultracold atomic platforms have been proven to be challenging, with experiments strongly limited by coherence times of few tens of milliseconds. In fact, the small energy scale of spin excitations reflects in a high sensitivity coupling to environmental magnetic noise, which affects the resonant condition. The experimental apparatus on which I worked during my Ph.D. solve this problem employing a magnetic shield that surrounds the science chamber, attenuating external magnetic fields by 6 orders of magnitudes. During my Ph.D., I investigated the properties of a coherently coupled mixture of BEC of Sodium 23, performing different experiments in two atomic configurations. The first configuration consist of a mixture of hyperfine states, namely the |F=1, mF = -1> and |F=1, mF = +1>, coupled by a two-photon transition, which is characterized by miscibility in the ground state. Another configuration was instead realized working with a strongly immiscible mixture of |F=1, mF=-1> and |F=2, mF = -2>, realized through with a one photon transition. My first experiment was devoted to the characterization of different methods of manipulation of the coupled miscible mixture in an elongated quasi-1D geometry. In Local Density Approximation (LDA), The dynamics of the system, depends on the atom number difference, the relative phase, and coupling to mean field energy ratio, can be fully described as an internal Josephson junction. We characterized this dynamics on a sample an inhomogeneous spatial profile, developing three different protocols for state manipulations. In a second experiment, I developed a protocol to generate Faraday waves in an unpolarized miscible mixture. Faraday waves are classical non-linear waves characterized by a regular pattern, that originate in classical and quantum fluids via a parametric excitation in the fluid. Interestingly enough, this process resembles the phase of reheating of the early universe, where the oscillation of the inflaton field is thought to have excited particles out of the vacuum. In analogy with this phenomenon, the oscillation of the inflaton field can be simulated with the periodic modulation of the trapping potential. On top of this, in a spin mixture, the parametric modulation can excite either in-phase (density) modes or out-of-phase (spin) modes, as two possible elementary excitations are present in the system. By extracting the spatial periodicity of the generated pattern at different modulation frequencies, I was then able to measure the dispersion relations for both density and spin modes of the system. In the presence of the coherent coupling, when spin excitations becomes gapped, we further demonstrate the scaling of the gap with the strength of the coupling radiation. The third experiment I realized concerned the characterization of the magnetic ground state of a spatially extended immiscible mixture in the presence of the coherent coupling. The Hamiltonian of such a system is formally equivalent to a continuous version of the transverse field Ising model, which describes magnetic materials at zero temperature. In this mapping, a nonlinear interaction term arises from the ratio between the self-interaction energy and the strength of the coupling, which acts as the transverse field. As the ratio between the two quantities is varied above and below one, the ground state of the system spontaneously changes from a paramagnetic phase to an ordered ferromagnetic phase, featuring two equivalent and opposite magnetizations, a signature of the occurrence of a second order quantum phase transition (QPT). Furthermore, in the magnetic model, the degeneracy between the two ferromagnetic ground states can be broken by introducing an additional longitudinal field. In the atomic case, the role of this additional field is taken by the detuning between the coupling radiation and the resonant transition frequency of non-interacting atoms. I characterized the QPT developing protocols to manipulate the spin mixture in its spatially extended ground state, varying the longitudinal field. Leveraging on the inhomogeneity of a BEC trapped in the harmonic potential, a smooth variation of the spin self-interaction energy occurs spontaneously in space, introducing different magnetic regimes at fixed coupling strength. These protocols gave access to a characterization of static properties typical of magnetic materials, such as the presence of an hysteresis cycle. The occurrence of the phase transition was instead validated by a measurement of the magnetic susceptibility and corresponding fluctuations, which both show a divergence when crossing the QPT critical point. At last, I developed a protocol to smoothly manipulate the position of magnetic domain walls, the least energetic excitations in a ferromagnet. While the previous study focused on static properties, the last experimental investigation presented in this thesis was devoted to the study of the dynamics of the metastable ferromagnetic region of the BEC. As a result of the presence of an hysteresis cycle, it is possible to engineer states of the ferromagnetic energy landscape that are homogeneously prepared either in the global minimum, with trivial dynamics, or in the metastable, higher energy, local minima. In the latter case, a classical system should eventually decay towards the global minimum, driven by temperature fluctuations which overtop the energy barrier separating the two minima. For a quantum system described by a field theory, such as a ferromagnetic BEC, the decay towards the global minimum occurs by tunneling through the barrier, triggered by quantum fluctuations. The event of tunneling is known as False Vacuum Decay (FVD), and is of outstanding relevance also for high energy physics and cosmology, were the first theoretical models were developed. In the FVD model, the decay towards the global minimum, the true vacuum, is a stochastic process that occurs only if a resonant bubble of true vacuum is formed. Once formed, the bubble will eventually expand throughout the whole system, as the true vacuum is energetically favorable. The probability for such a bubble to form can be approximately calculated analytically in 1D, and should depend exponentially on the height of the barrier the field has to tunnel through. Due to the exponentially long time scale of the process, experimental observations of FVD were still lacking. Thanks to the enhanced coherence time of the superfluid ferromagnetic mixture, and to the precise control of the barrier height through the detuning from atomic resonance, we were able to observe the event of bubble nucleation in a ferromagnetic BEC. To corroborate the observation, I measured the characteristic timescale of the decay for different values of the control parameters. Results were successfully compared first with numerical simulation, and then validated by instanton theory.

No description available.

This thesis presents novel radio frequency microelectromechanical (RF MEMS) circuits based on the three-dimensional (3-D) micromachined coplanar transmission lines whose geometry is re-configured by integrated microelectromechanical actuators. Two types of novel RF MEMS devices are proposed. The first is a concept of MEMS capacitors tuneable in multiple discrete and well-defined steps, implemented by in-plane moving of the ground side-walls of a 3-D micromachined coplanar waveguide transmission line. The MEMS actuators are completely embedded in the ground layer of the transmission line, and fabricated using a single-mask silicon-on-insulator (SOI) RF MEMS fabrication process. The resulting device achieves low insertion loss, a very high quality factor, high reliability, high linearity and high self actuation robustness. The second type introduces two novel concepts of area efficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. The coupling is achieved by tuning both the ground and the signal line coupling, obtaining a large tuneable coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity over a very large bandwidth. This thesis also presents for the first time on RF nonlinearity analysis of complex multi-device RF MEMS circuits. Closed-form analytical formulas for the IIP3 of MEMS multi-device circuit concepts are derived. A nonlinearity analysis, based on these formulas and on  measured device parameters, is performed for different circuit concepts and compared to the simulation results of multi-device  conlinear electromechanical circuit models. The degradation of the overall circuit nonlinearity with increasing number of device stages is investigated. Design rules are presented so that the mechanical parameters and thus the IIP3 of the individual device stages can be optimized to achieve a highest overall IIP3 for the whole circuit.The thesis further investigates un-patterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip inductances. The approach used is to increase the thickness of the ferromagnetic material without increasing its conductivity, by using multilayer NiFe and AlN sandwich structure. This suppresses the induced currents very effectively and at the same time increases the ferromagnetic resonance, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. The so far highest permeability values above 1 GHz for on-chip integrated un-patterned NiFe layers were achieved. / <p>QC 20140328</p>

Le transport et la distribution de l'énergie électrique sont traditionnellement réalisés en alternatif (50 Hz ou 60 Hz), un des éléments-clés de ces infrastructures est le transformateur de puissance. Ce dernier est utilisé depuis plus d'un siècle et donc sa conception est maîtrisée (avec des rendements très élevés, supérieurs à 99 %). Depuis quelques années, la part des énergies renouvelables est en constante augmentation. Bien souvent, la production des énergies renouvelables est éloignée des centres de consommation. Or, le transport en courant continu sous haute tension (HVDC) sur de grandes distances est plus rentable. Dans ce cas, nous avons besoin de convertisseurs de puissance fonctionnant pour certains avec des Transformateurs Moyennes Fréquences (TMF) entre 1 kHz et quelques dizaines de kilohertz. Dans ces applications, la recherche du rendement maximal est primordiale. L'augmentation de la fréquence de fonctionnement a pour effet bénéfique de diminuer l'encombrement d'un transformateur. Cependant un certain nombre de problèmes vont apparaître avec cette augmentation. Nous pouvons citer : les pertes dans les conducteurs et dans le circuit magnétique sont liées à la fréquence ; le type de bobinages (fil de Litz et feuillard) et les matériaux magnétiques (ferrites et nanocristallins) en moyennes fréquences sont différents de ceux utilisés en 50 Hz ; le refroidissement est plus complexe car la densité de puissance volumique est plus élevée... Ainsi dans cette thèse, nous avons mis en place une méthodologie de conception afin de maîtriser au mieux le dimensionnement d'un TMF avec un compromis précision et coût de calculs. Nous avons identifié les modèles (analytiques et numériques) susceptibles d'être utilisés pour estimer les performances d'un TMF. Deux TMF d'une puissance de 180 kVA et de 1 kVA ont été dimensionnés, fabriqués et testés afin de mettre en évidence le domaine de validité et d'ajuster les différents modèles. Ce travail nous a permis de mettre en place une méthodologie de conception allant des spécifications du convertisseur jusqu'à la simulation de celui-ci avec le modèle du transformateur dimensionné. Nous avons mis en évidence : l'influence de paramètres technologiques sur l'élévation de la résistance pour des bobinages de type feuillard et l'influence de paramètres technologiques sur les propriétés magnétiques des matériaux nanocristallins. Ce travail de thèse a été réalisé avec le groupe « Matériaux du Génie Electrique » du laboratoire Ampère et financé par l'institut pour la transition énergétique SuperGrid Institute / The transmission and distribution of electric power is normally made by ac networks (50 Hz or 60 Hz), where one of the key elements of this infrastructure is the power transformer; used for more than a century, its design is very well understood, with a level of operating efficiency normally greater than 99%. In recent years, the share of renewable energy has been increasing. Often times the energy generated from renewable sources is produced far from consumption centers, and so transportation in the form of high voltage direct current (HVDC) over long distances is more profitable, due to the lower losses seen than with HVAC after a certain length of transmission line. In this case, we need power converters operating with Medium Frequency Transformers (MFT) from 1 kHz to tens of kilohertz. For these applications, the research of their maximum efficiency in operation is paramount. Increasing the transformer operating frequency has the beneficial effect of reducing its size. However, a number of problems will appear with this frequency increase, such as: the increase in the losses in the conductors and the magnetic circuit that are related to the frequency; the less well understood winding type (Litz wire and foil) and magnetic materials (ferrites and nanocrystalline) in the MF that are different from those used at 50 Hz; the cooling is more complex because the power density is higher, etc. In this thesis, a design methodology was developed in order to optimise the design of MFTs with respect to the compromise between accuracy and the length of calculations. In addition, analytical and numerical models were identified that can be used to accurately estimate the performance of an MFT. Furthermore, two MFTs (apparent power: 180 kVA and 1 kVA, respectively) were sized, manufactured and tested in order to demonstrate the domain of validity of the models, and also for optimisation of the different models. This work has enabled the development of a design methodology using the converter specifications and build a simulation with complete model of the transformer, which can then be used to validate an MFT design. We have highlighted: the influence of the technological parameters on the rise of resistance in the foil coils and the influence of the technological parameters on the magnetic properties of nanocrystalline materials. This work was performed with the group "Materials for Electrical Engineering" Ampère laboratory and funded by the Institute for Energy Transition SuperGrid Institute.

Neue elektrische Antriebskonzepte ermöglichen es, eine hohe Funktionalität in einem eingeschränkten Bauraum unterzubringen. Damit steigt auch in der Landwirtschaft das Interesse an elektrischen Antrieben. Die Projektgruppe Elektrische Maschinen und Antriebe der HTW Dresden beteiligt sich mit der TU Dresden an einem Projekt, bei dem beginnend mit der elektrisch angetriebenen Dreschtrommel umfassend an einem Mähdrescher untersucht wird, wie diese Antriebe in einzelne Funktionselemente integriert werden können. Neben der Auslegung der Antriebe werden Verfahren erarbeitet, die Verluste im Motor mit hoher Genauigkeit zu berechnen. So können in Zukunft passgenaue Kühlkonzepte für diese Antriebstechnik entwickelt werden. Anforderungen gerade im Bereich der Elektromobilität fordern den Blick für neue Materialien, deren elektromagnetisches und thermisches Verhalten werden in ihrem Einfluss auf die Erwärmung untersucht. Analytische und kombinierte Berechnungsmethoden in 2D-FEM gestatten die vereinfachte Rechnung unter Berücksichtigung von Grundwelle und entstehenden Harmonischen zu qualifizieren. Verlustberechnungen aus der transienten FEM-Rechnung ermöglichen diese Verbesserung. Die Methode wird am Beispiel der elektrischen Dreschtrommel mit den berechneten Verlustverteilungen beschrieben. Neue Methoden der 3D-FEM, wie sie die Software Ansys bietet, werden für die Nutzung von Einflüssen der Wirbelstromeffekte und in Auswertung für die Segmentierung von Permanentmagneten dargestellt. Die exemplarisch gewonnenen Erkenntnisse liefern einen Beitrag für weitere Schneidwerksantriebe am Mähdrescher, aber auch darüber hinaus in Projekten mit Herstellern elektrischer Maschinen. / New concepts for electrical drives make it possible to put a high functionality into a restricted structural form. Thereby the interest in electrical drives increases also in the farming. The project team Electrical machines and drives of the HTW Dresden participates together with the TU Dresden in a project, where starting with the electrically driven threshing cylinder is comprehensively examined at a combine harvester, how these drives can be integrated into single function elements. Besides the dimensioning of the drives are developed methods to calculate losses in the engine with high precision. So custom-fit cooling concepts can be developed for this drive technology in future. Requirements just in the area of the electric mobility call looking for new materials, whose electromagnetic and thermic behavior are examined in her influence on the warming. Analytical and combined computation methods in 2D-FEM allow the simplified calculation under consideration of the fundamental wave and the arising harmonic ones. Loss calculations by means of the transient FEM calculation make possible this improvement. The method is described at the example of the electrical threshing cylinder with the calculated loss distributions. New methods of the 3D-FEM, as the software of Ansys offers, are presented for the use of influences of the eddy current effects and in evaluation for the segmentation of permanent magnets. The exemplarily got knowledge provides a contribution for further cut header drives at the combine but also furthermore in projects together with manufacturers of electrical machines.

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.

In this work, our initial efforts have been directed to study the behavior of the magnetization as a function of temperature, calculated according to the approximate method of the anisotropy constants and the resolution of a Hamiltonian (that includes the crystal field) as exemplified for the DyAl2 compound. Furthermore, we investigated the magneto-thermal characteristics of some members of the RX2 series (R: rare earth, X: Al, Ni), including spin reorientation (SR), by using a model Hamiltonian, that consists of localized magnetic moments interacting via exchange and crystal field interaction, in the molecular-field approximation. We studied how the SR depends on the direction of the application of magnetic field, the intensity of this field and temperature. For the magnetic calculations, the problem of self-consistency was solved by using a computational routine developed in the Fortran 90 programming language. We emphasize that special attention was directed to the crystal field, because of its high relevance to the anisotropic characteristics of the RX2 studied compounds. Thus, in our attempts to study the peculiarities of the rare earth elements, due to crystal field effects, we have not only considered the intensity change, but the direction change of the applied field. In the cases of both Er+3 and Tb+3 compounds, we obtained second-order or continuous magnetization behavior along the polar angle axis. We stressed that the crystal field terms plays an important role in the first order spin reorientation for Dy+3 and Ho+3 compounds. First, it can be revealed by the discontinuity in the Cartesian components of the magnetization vector as a function of the polar angle. Second, the discontinuity is of great importance in the calculation of latent heat associated to the spin reorientation in the case where the first order transitions were observed. Finally, we were able to separate the first and second order contributions of the anisotropic magnetic entropy change, which is the main result of this work. / Neste trabalho, nossos esforços iniciais foram direcionados a estudar o comportamento da magnetização em função da temperatura, calculado segundo o método aproximativo das constantes de anisotropia e da resolução de um hamiltoniano (que inclui o campo cristalino) como exemplificado para o composto DyAl2. Além disto, investigamos as características magneto-térmicas de alguns integrantes da série RX2 (R: Terra rara; X: Al, Ni), incluindo a reorientação de spin (RS), usando um hamiltoniano modelo que consiste de momentos magnéticos localizados interagentes via interações de troca e de campo cristalino, na aproximação do campo molecular. Estudamos como a RS depende da direção de aplicação do campo magnético, da sua intensidade e da temperatura. Para os cálculos magnéticos, o problema da auto consistência foi solucionado utilizando uma rotina, computacional desenvolvida na linguagem computacional Fortran 90. Ressaltamos que, uma atenção especial foi direcionada ao campo cristalino, por conta da sua alta relevância sobre as características anisotrópicas dos compostos RX2 estudados. Portanto, em nossas tentativas para estudar as peculiaridades dos elementos terras raras, devido aos efeitos do campo cristalino, não consideramos somente a mudança na intensidade, mas a variação na direção do campo aplicado. No caso dos compostos Er+3 e Tb+3, obteve-se um comportamento da magnetização de segunda ordem ou contínuo face à mudança do ângulo polar. Salientamos que os termos de campo cristalino desempenham um papel fundamental na reorientação de spin de primeira ordem para Dy+3 e Ho+3. Primeiro, tal transição pode ser revelada por uma descontinuidade nas componentes cartesianas do vetor de magnetização em função do ângulo polar. Segundo, a descontinuidade é de grande importância para o cálculo do calor latente associado à reorientação spin nos casos em que foram observadas as transições de primeira ordem. Finalmente, foi possível separar as contribuições de primeira e segunda ordem da variação de entropia magnética anisotrópica, o qual é o principal resultado deste trabalho.

Neue elektrische Antriebskonzepte ermöglichen es, eine hohe Funktionalität in einem eingeschränkten Bauraum unterzubringen. Damit steigt auch in der Landwirtschaft das Interesse an elektrischen Antrieben. Die Projektgruppe Elektrische Maschinen und Antriebe der HTW Dresden beteiligt sich mit der TU Dresden an einem Projekt, bei dem beginnend mit der elektrisch angetriebenen Dreschtrommel umfassend an einem Mähdrescher untersucht wird, wie diese Antriebe in einzelne Funktionselemente integriert werden können. Neben der Auslegung der Antriebe werden Verfahren erarbeitet, die Verluste im Motor mit hoher Genauigkeit zu berechnen. So können in Zukunft passgenaue Kühlkonzepte für diese Antriebstechnik entwickelt werden. Anforderungen gerade im Bereich der Elektromobilität fordern den Blick für neue Materialien, deren elektromagnetisches und thermisches Verhalten werden in ihrem Einfluss auf die Erwärmung untersucht. Analytische und kombinierte Berechnungsmethoden in 2D-FEM gestatten die vereinfachte Rechnung unter Berücksichtigung von Grundwelle und entstehenden Harmonischen zu qualifizieren. Verlustberechnungen aus der transienten FEM-Rechnung ermöglichen diese Verbesserung. Die Methode wird am Beispiel der elektrischen Dreschtrommel mit den berechneten Verlustverteilungen beschrieben. Neue Methoden der 3D-FEM, wie sie die Software Ansys bietet, werden für die Nutzung von Einflüssen der Wirbelstromeffekte und in Auswertung für die Segmentierung von Permanentmagneten dargestellt. Die exemplarisch gewonnenen Erkenntnisse liefern einen Beitrag für weitere Schneidwerksantriebe am Mähdrescher, aber auch darüber hinaus in Projekten mit Herstellern elektrischer Maschinen. / New concepts for electrical drives make it possible to put a high functionality into a restricted structural form. Thereby the interest in electrical drives increases also in the farming. The project team Electrical machines and drives of the HTW Dresden participates together with the TU Dresden in a project, where starting with the electrically driven threshing cylinder is comprehensively examined at a combine harvester, how these drives can be integrated into single function elements. Besides the dimensioning of the drives are developed methods to calculate losses in the engine with high precision. So custom-fit cooling concepts can be developed for this drive technology in future. Requirements just in the area of the electric mobility call looking for new materials, whose electromagnetic and thermic behavior are examined in her influence on the warming. Analytical and combined computation methods in 2D-FEM allow the simplified calculation under consideration of the fundamental wave and the arising harmonic ones. Loss calculations by means of the transient FEM calculation make possible this improvement. The method is described at the example of the electrical threshing cylinder with the calculated loss distributions. New methods of the 3D-FEM, as the software of Ansys offers, are presented for the use of influences of the eddy current effects and in evaluation for the segmentation of permanent magnets. The exemplarily got knowledge provides a contribution for further cut header drives at the combine but also furthermore in projects together with manufacturers of electrical machines.

<p dir="ltr">Probabilistic computing is a novel computing scheme that offers a more efficient approach than conventional complimentary metal-oxide-semiconductor (CMOS)-based logic in a variety of applications ranging from Bayesian inference to combinatorial optimization, and invertible Boolean logic. These applications, which have found use in the rapidly growing fields of machine learning and artificial intelligence, are traditionally computationally-intensive and so make the push for novel computing schemes that are intrinsically low-power and scalable all the more urgent.</p><p dir="ltr">The probabilistic bit (or p-bit, the base unit of probabilistic computing) is a naturally fluctuating entity that requires <i>tunable </i>stochasticity; low-barrier nanomagnets, in which the magnetic moment fluctuates randomly and continuously due to the presence of thermal energy, are a natural vehicle for providing the core functionality required. This dissertation describes the work done in mining the rich field of spintronics to produce devices that can act as natural hardware accelerators for probabilistic computing algorithms.</p><p dir="ltr">First, experiments exploring Fe₃O₄ nanoparticles as naturally stochastic systems are presented. Using NV center measurements on an array of such nanoparticles, it is shown that they fluctuate intrinsically at GHz frequencies at room temperature; these fluctuations could be harnessed to act as a stochastic noise source, and would, in principle, enable fast computation.</p><p dir="ltr">The focus then shifts to the development of a platform that allows for easier <i>electrical</i> readout: the low-barrier magnetic tunnel junction (MTJ). We show the work done in the development and characterization of these devices, how they respond to non-ideal environments, such as elevated temperatures and exposure to high-energy electromagnetic radiation, how their intrinsic stochasticity might be tuned with electrical currents and external magnetic fields, and then how these might be integrated with a simple transistor circuit to produce a compact low-energy implementation of a p-bit.</p><p dir="ltr">Next, by integrating our stochastic MTJs with 2D-MoS₂field-effect transistors (FETs), the first <i>on-chip </i>realization of a key p-bit building block, displaying voltage-controllable stochasticity, is demonstrated. This is followed by another key demonstration through the fabrication of stochastic MTJs directly on top of an integrated circuit platform, where the transistor circuitry is provided by 180nm-node CMOS technology.</p><p dir="ltr">In addition, supported by circuit simulations, this work provides a careful device-level analysis of the three transistor-one magnetic tunnel junction (3T-1MTJ) p-bit design, evaluating how the characteristics of each component can influence the overall p-bit’s output. In particular, we show that – against common wisdom – a large tunnel magnetoresistance (TMR) is not the best choice for p-bits; bimodal telegraphic fluctuations are highly undesirable and are a sign of a slow device; and an ideal inverter with a large gain is unsuitable for p-bit applications due to the higher likelihood of unwanted plateaus in the resulting p-bit’s output.</p><p dir="ltr">This analysis is extended to consider the impact of such non-ideal p-bits when used to construct probabilistic circuits, with the focus on the emulation of the Boolean logic AND gate through a three p-bit correlated system. It is found that a probabilistic circuit made with ideal p-bits can accurately emulate the function of an AND gate, while the non-ideal p-circuits suffer from an increased error rate in emulating the AND gate’s truth table.</p><p dir="ltr">The understanding gained at the individual device level, in what makes a good or bad MTJ, to how the different components of the 3T-1MTJ p-bit can affect its output, and subsequently how non-ideal p-bits can impact circuit performance, can be important for the future realization of scaled on-chip p-bit networks.</p>

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