The sensor is a device that converts a form of energy concerning which the information is sought, called the measurand, to a form (electrical) in which it can be usefully processed or interpreted. Sensors rely on physical or chemical phenomena and materials where those phenomena appear to be useful. Those phenomena may concern the material itself or its geometry. Hence, the major innovations in sensors come from new materials, new fabrication techniques or both. Normally, thin film sensors are realized by depositing a sensing film on a suitable substrate. There could be many combination of metals and insulating materials being deposited depending upon the application or sensing requirements. In general, sensors for various applications are fabricated using a variety of liquid phase technologies (also called as wet methods) and gas phase technologies (also called as dry methods) of deposition. Hence sensor fabrication technology requires various combination of processing technologies and newer materials. In the present work, an attempt is made to design and fabricate a thin film based pressure sensor using a combination of wet and dry deposition techniques. The diaphragm, used for sensing the pressure is coated with a hard anodic coating (Al2O3) using a wet technology, viz. pulse hard anodizing technique, for electrical insulation requirement. The piezo-resistive strain sensing films were deposited onto this coating by dry method, namely, DC Magnetron sputtering technique.. Chapter 01 gives a brief overview of sensors, their classification, principles of sensing,characteristics, materials used in the fabrication of sensors like conductors and insulators, the components of a sensor. Chapter 02 gives brief information about various techniques of depositions viz., liquid phase technologies (wet methods) and vapour phase technologies (dry methods) used to fabricate the sensors. Also, information regarding the coating property evaluation and coating characterization techniques is included. The chapter 03 presents a detailed account of work carried out to obtain an electrically insulating layer by the development of pulse hard anodizing process for aluminum alloy diaphragm, necessary process optimization and testing. The details related to the development, fabrication and testing of thin film based pressure sensors using aluminum alloy diaphragm with hard anodic coating are presented in Chapter 04. The thin film strain gauges were deposited using DC magnetron sputtering technique. The information about mask design, deposition process parameters, calibration etc is also included. Chapter 05 provides summary of the work carried out and conclusions. The scope of carrying out further work is also outlined.

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, 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

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.