Gegenwärtige Bestrebungen materialwissenschaftlicher Forschung beschäftigen sich unter anderem mit der Überführung zweidimensionaler Elemente elektronischer, optischer, plasmonischer oder magnetischer Funktionalität in den dreidimensionalen (3D) Raum. Dieser Ansatz vermag mittels Krümmung und struktureller Topologie bereits vorhandene Eigenschaften abzuändern beziehungsweise neue Funktionalitäten bereitzustellen. Vor allem Vektoreigenschaften wie die Magnetisierung kondensierter Materie lassen sich aufgrund der Brechung der Inversionssymmetrie in gekrümmten Flächen stark beeinflussen. Neben der Entwicklung diverser Vorgänge zur Herstellung 3D magnetischer Gegenstände sind geeignete Untersuchungsmethoden wie beispielsweise tomografische Abbildungen der Magnetisierung von Nöten, die maßgeblich die physikalischen Eigenschaften bestimmen. Die vorliegende Dissertationsschrift befasst sich mit der Abbildung von magnetischen Domänen in 3D gekrümmten Dünnschichten beruhend auf dem Effekt des zirkularen magnetischen Röntgendichroismus (XMCD). Die in diesem Zusammenhang entwickelte magnetische Röntgentomografie (MXT) basierend auf weicher Röntgenmikroskopie stellt eine zu Elektronenholografie und Neutronentomografie komplementäre Methodik dar, welche großes Anwendungspotential in der elementspezifischen Untersuchung magnetischer gekrümmter Flächen mit örtlicher Auflösung im Nanometerbereich aufweist. Die Schwierigkeit der Interpretation von Abbildungen magnetischer Strukturen in gekrümmten Flächen rührt von der Dreidimensionalität und der Vektoreigenschaft der Magnetisierung her. Die hierzu notwendigen Kenntnisse sind anhand von zwei topologisch verschiedenen Flächen in Form hemisphärischer Kappen und hohler Zylinder erschlossen worden. Die praktische Anwendung von MXT ist abschließend anhand der Rekonstruktion magnetischer Domänen in aufgerollten Dünnschichten mit zylindrischer Form verdeutlicht. / One of the foci of modern materials sciences is set on expanding conventional two-dimensional electronic, photonic, plasmonic and magnetic devices into the third dimension. This approach provides means to modify conventional or to launch novel functionalities by tailoring curvature and three-dimensional (3D) shape. The degree of effect is particularly high for vector properties like the magnetization due to an emergent inversion symmetry breaking. Aside from capabilities to design and synthesize 3D magnetic architectures, proper characterization methods, such as magnetic tomographic imaging techniques, need to be developed to obtain a thorough understanding of the system’s response under external stimuli. The main objective of this thesis is to develop a visualization technique that provides nanometer spatial resolution to image the peculiarities of the magnetic domain patterns on extended 3D curved surfaces. The proposed and realized concept of magnetic soft X-ray tomography (MXT), based on the X-ray magnetic circular dichroism (XMCD) effect with soft X-ray microscopies, has the potential to become a powerful tool to investigate element specifically an entirely new class of 3D magnetic objects with virtually any shape and magnetization. Imaging curved surfaces meets the challenge of three-dimensionality and requires a profound understanding of the recorded XMCD contrast. These experiences are gained by visualizing magnetic domain patterns on two distinct 3D curved surfaces, namely magnetic cap structures and rolled-up magnetic nanomembranes with cylindrical shape. The capability of MXT is demonstrated by reconstructing the magnetic domain patterns on 3D curved surfaces resembling hollow cylindrical objects.

Micro-technology relies on a highly parallel fabrication of 2D electronic and/or microelectromechanical devices, where in most cases silicon wafers are used as substrates. In contrast 3D fabrication shows unique advantages, such as footprint reduction or the possibility to obtain additional functionalities. For example, in the case of a sensor, knowledge of the acceleration in all possible directions, the surrounding electric or magnetic field among other quantities can help to determine the exact position of an object in 3D space. To do that it is crucial to retrieve all components of a vector field, which requires at least one out of plane component. In other fields like integrated optics three dimensional structures can enhance the coupling efficiency with free space interactions. As such 3D micro-structures will be crucial for upcoming products and devices. A highly parallel fabrication is required to enable mass-adaption, self-assembly is an emerging technology that could deliver this purpose. Examples of 3D structures created by self-assembly include polyhedrons like cubes, pyramids or micro tubular structures such as tubes or spirals. Following a self assembly scheme, 3D devices would be created through the fabrication of standard 2D structures that are reshaped through a self-assembly step into a 3D object. In this thesis a novel dry release protocol was developed to roll-up strained nanomembranes from a silicon sacrificial layer employing dry fluorine chemistry. This way a wet release is totally circumvented thus preventing damage of the created structures due to turbulent flow or capillary forces. Additionally the developed process enabled the use of standard CMOS deposition and processing tools, leading to a high increase in yield and quality, with yields exceeding 99% for microtubes. Building on the developed technology various devices where fabricated, for example rolled-up micro capacitors at a wafer scale with an increased yield and a low spread of electrical characteristics. For the E12 industrial standard more than 90% of devices behaved within the required performance characteristics. Furthermore the yield and Q-factor of roll-up whispering gallery mode resonators was strongly improved, making it possible to self assemble 3D coupled photonic molecules, which showed a mode splitting exceeding the FSR, as well as hybrid supermodes at points of energy degeneracy.:Contents Bibliographic Record i List of Abbreviations vii List of Chemical Substances ix 1 Introduction 1 1.1 Microelectromechanical Systems 1 1.2 Strain Engineering 2 1.3 Rolled - Up Nanotechnology 3 1.4 Objective and Structure of the Thesis 5 2 Materials and Methods 9 2.1 Fabrication Techniques 9 2.1.1 Substrates 9 2.1.2 Plasma Enhanced Chemical Vapor Deposition 9 2.1.3 Dry Etching12 2.1.4 Deep Reactive Ion Etching 18 2.1.5 Atomic Layer Deposition 19 2.1.6 Lithography 20 2.2 Characterization Techniques 22 2.2.1 Strain Measurement 22 2.2.2 Ellipsometry 23 3 Dry Roll-Up of Strained Nanomembranes 25 3.1 Rolled - Up Nanotechnology 25 3.2 Fabrication 26 3.2.1 Release 29 3.3 Conclusions 33 4 Rolled-UpMicro Capacitors 35 4.1 Micro Capacitors 35 4.2 Fabrication 38 4.3 Characterization 39 4.4 Conclusion 41 5 Optical Micro-Cavities 43 5.1 Optical Micro Cavities 43 5.2 Theorectical Background 45 5.2.1 Quality - factor 49 5.2.2 FDTD 52 6 Optical Microtube Resonators 55 6.1 Optical Whispering Gallery Mode Microtube Resonators 55 6.2 Fabrication 57 6.3 Active Characterization 60 6.4 Conclusions 64 7 Photonic Molecules 65 7.1 Coupled Photonic Systems 65 7.2 Fabrication 68 7.3 Device Characterization 71 7.4 Multimode Waveguides 84 7.5 Conclusions 85 8 Conclusions and Outlook 87 8.1 Conclusions 87 8.2 Outlook 88 Bibliography 91 List of Figures 109 List of Tables 117 A Equipment 119 Cover Pages 121 Selbstständigkeitserklärung 123 Acknowledgements 125 List of Publications 127 List of Presentations 129 Curriculum Vitae 131

This thesis addresses the development of materials, technologies and circuits applied for the fabrication of a new class of microelectronic devices that are relying on a three-dimensional shape variation namely shapeable microelectronics. Shapeable microelectronics has a far-reachable future in foreseeable applications that are dealing with arbitrarily shaped geometries, revolutionizing the field of neuronal implants and interfaces, mechanical prosthetics and regenerative medicine in general. Shapeable microelectronics can deterministically interface and stimulate delicate biological tissue mechanically or electrically. Applied in flexible and printable devices shapeable microelectronics can provide novel functionalities with unmatched mechanical and electrical performance. For the purpose of shapeable microelectronics, novel materials based on metallic multilayers, photopatternable organic and metal-organic polymers were synthesized. Achieved polymeric platform, being mechanically adaptable, provides possibility of a gentle automatic attachment and subsequent release of active micro-scale devices. Equipped with integrated electronic the platform provides an interface to the neural tissue, confining neural fibers and, if necessary, guiding the regeneration of the tissue with a minimal impact. The self-assembly capability of the platform enables the high yield manufacture of three-dimensionally shaped devices that are relying on geometry/stress dependent physical effects that are evolving in magnetic materials including magentostriction and shape anisotropy. Developed arrays of giant magnetoimpedance sensors and cuff implants provide a possibility to address physiological processes locally or distantly via magnetic and electric fields that are generated deep inside the organism, providing unique real time health monitoring capabilities. Fabricated on a large scale shapeable magnetosensory systems and nanostructured materials demonstrate outstanding mechanical and electrical performance. The novel, shapeable form of electronics can revolutionize the field of mechanical prosthetics, wearable devices, medical aids and commercial devices by adding novel sensory functionalities, increasing their capabilities, reducing size and power consumption.

This thesis addresses the development of materials, technologies and circuits applied for the fabrication of a new class of microelectronic devices that are relying on a three-dimensional shape variation namely shapeable microelectronics. Shapeable microelectronics has a far-reachable future in foreseeable applications that are dealing with arbitrarily shaped geometries, revolutionizing the field of neuronal implants and interfaces, mechanical prosthetics and regenerative medicine in general. Shapeable microelectronics can deterministically interface and stimulate delicate biological tissue mechanically or electrically. Applied in flexible and printable devices shapeable microelectronics can provide novel functionalities with unmatched mechanical and electrical performance. For the purpose of shapeable microelectronics, novel materials based on metallic multilayers, photopatternable organic and metal-organic polymers were synthesized. Achieved polymeric platform, being mechanically adaptable, provides possibility of a gentle automatic attachment and subsequent release of active micro-scale devices. Equipped with integrated electronic the platform provides an interface to the neural tissue, confining neural fibers and, if necessary, guiding the regeneration of the tissue with a minimal impact. The self-assembly capability of the platform enables the high yield manufacture of three-dimensionally shaped devices that are relying on geometry/stress dependent physical effects that are evolving in magnetic materials including magentostriction and shape anisotropy. Developed arrays of giant magnetoimpedance sensors and cuff implants provide a possibility to address physiological processes locally or distantly via magnetic and electric fields that are generated deep inside the organism, providing unique real time health monitoring capabilities. Fabricated on a large scale shapeable magnetosensory systems and nanostructured materials demonstrate outstanding mechanical and electrical performance. The novel, shapeable form of electronics can revolutionize the field of mechanical prosthetics, wearable devices, medical aids and commercial devices by adding novel sensory functionalities, increasing their capabilities, reducing size and power consumption.