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Polycrystalline SiGe has emerged as a promising MEMS (Microelectromechanical Systems) structural material since it provides the desired mechanical properties at lower temperatures compared to poly-Si, allowing the direct post-processing on top of CMOS. This CMOS-MEMS monolithic integration can lead to more compact MEMS with improved performance. The potential of poly-SiGe for MEMS above-aluminum-backend CMOS integration has already been demonstrated. However, aggressive interconnect scaling has led to the replacement of the traditional aluminum metallization by copper (Cu) metallization, due to its lower resistivity and improved reliability. Poly-SiGe for MEMS-above-CMOS sensors demonstrates the compatibility of poly-SiGe with post-processing above the advanced CMOS technology nodes through the successful fabrication of an integrated poly-SiGe piezoresistive pressure sensor, directly fabricated above 0.13 m Cu-backend CMOS. Furthermore, this book presents the first detailed investigation on the influence of deposition conditions, germanium content and doping concentration on the electrical and piezoresistive properties of boron-doped poly-SiGe. The development of a CMOS-compatible process flow, with special attention to the sealing method, is also described. Piezoresistive pressure sensors with different areas and piezoresistor designs were fabricated and tested. Together with the piezoresistive pressure sensors, also functional capacitive pressure sensors were successfully fabricated on the same wafer, proving the versatility of poly-SiGe for MEMS sensor applications. Finally, a detailed analysis of the MEMS processing impact on the underlying CMOS circuit is also presented.

Optics. Quantum optics --- Electronics and optics of solids --- Physics --- Surface chemistry --- Chemical structure --- Materials sciences --- Electrical engineering --- Applied physical engineering --- Biotechnology --- materiaalkennis --- oppervlakte-onderzoek --- nanotechniek --- biotechnologie --- ingenieurswetenschappen --- fysica --- transistoren --- halfgeleiders --- elektrische circuits --- microwaves

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Metal additive manufacturing is more and more implemented in the space industry. Both private companies and space agencies are researching the advantages of and the possibilities with these innovative technologies. The technology that is currently most implemented is the laser powder bed fusion (LPBF) technology which is able to produce fully dense parts with complex geometries. In addition, the LPBF technology allows the production of small batch productions with customised parts which is ideal for the space industry. Though, there are still some challenges that need to be faced before the LPBF technology can be optimally implemented in the space industry. For this thesis project, a case study was selected to be used as a common thread throughout the investigations. A satellite bracket from Thales Alenia Space was selected as it includes many features needed for this research and recently qualified flight parts were successfully delivered. The satellite bracket is part of a telecommunication satellite and is used to clamp the antennas on the Earth-deck of the satellite during launch, as the excessive vibrations could cause damage. The parts were manufactured in Ti-6Al-4V ELI as the material reacts good to thermo-elastic stresses and has good stiffness. Based on these satellite brackets, the whole workflow from an additive manufacturing company to implement LPBF technology in the space industry was implemented and investigated. After researching the current workflow for implementation of LPBF technology, two steps could be defined as drawbacks as they consume a lot of time and cost a lot of money. These steps being the ‘non-destructive testing’ step and the ‘machining (milling)’ step. For both steps, proposed optimisations were investigated to reduce the cost and lead time. For the ‘non-destructive testing’ step, the monitoring data analysis tool that is integrated in the CAD programme, 3DXpert, of the AM company, 3D Systems, was investigated and further developed. This tool supports the in-situ monitoring system created by the company and for this project lack of fusion porosities were investigated. For the ‘machining (milling)’ step a first implementation of ‘workflow’ software was investigated. The integrated CAD programme, 3DXpert, contains a machining tool developed to ease the programming of machining operations for additively manufactured parts. Compared to defects obtained from a CT scan, the monitoring data analysis tool achieve a 100% defect detection based on location. Though, this detection was accompanied by a high false positive count. This high false positive count is due to the current configuration of the algorithm which also outputs really small events that are not visible in a CT scan and the probability of lack of fusion defects that get sufficiently re-molten during the build process. The next step for this research is to reduce the false positive count using a volume filter and finding the optimal volume for optimal threshold values. For the machining tool, the first steps have been taken for further implementation of ‘workflow’ software in the industry. Current companies acknowledge the need for a better communication and file transfer systems to avoid misunderstandings that lead to errors. This thesis will be used as a first in its kind to make the potential benefits explicitly clear to all stakeholders of the manufacturing supply chain, enforcing future innovation in the implementation of LPBF technology in the

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Selective laser melting (SLM) is a powder-bed additive manufacturing process in which an object is built by selectively melting the fine powder by high-power laser in a layer-wise manner. It holds the advantage of producing complex-shaped parts with high density. For the concern of powder cross-contamination, the commercial SLM enables mostly the fabrication of single-material components in a single manufacturing operation. Recently, researchers have attempted to manufacture multi-material parts via the modified SLM methods. However, there are not yet commercially successful multi-material products fabricated by the modified SLM facilities. It thus requires not only machine modification but also the know-how to solidly join dissimilar metals under the laser-beam condition.The thesis aims to understand interfacial behaviours when manufacturing multi-materials by using SLM. To achieve this, four multi-material pairs, divided into three parts based on different base metals of 316L, Ti-6Al-4V and AlSi7Mg, were processed via commercial SLM. The first part analyzed the influence of SLM processing parameters on producing the interface of 316L/Hastelloy X. The second part compared the interfaces resulting from adding near-α titanium alloy (Ti-6Al-2Sn-4Zr-2Mo) and γ-TiAl (Ti-48Al-2Cr-2Nb) on the top of Ti-6Al-4V, respectively. Considering that Ti-6Al-2Sn-4Zr-2Mo is fully new material for SLM, the processibility and post-heat treatment of the alloy were also investigated in part 2. The third part studied the interface formed by SLM adding A357 (AlSi7Mg0.5) on the top of cast A356 (AlSi7Mg0.3). Since the high-rough cast surface may worsen the succeeding growth of A357, different surface treatments were compared in producing a strong interface. Then, these SLM-built multi-materials were characterized to understand the grain growth and material mixing at the interface region. Mechanical testing of the multi-materials was also conducted to verify the reliability of dissimilar joints.The study on multi-material 316L/Hastelloy X indicated that SLM parameter, particular the laser energy density, plays a critical role in forming a solid joint. Processed by the optimal parameters, the bimetal exhibited epitaxial grain growth from 316L to Hastelloy X, without deadly defects at the interface. The subsequent tensile testing also confirmed a robust bonding between 316L and Hastelloy X.By comparing the two titanium-based bimetals in terms of their SLM processibility and interfacial formation, it was found that Ti-6Al-4V/γ-TiAl displayed a much wider interface than Ti-6Al-4V/Ti-6Al-2Sn-4Zr-2Mo, despite under the similar processing parameters. The interfacial width difference is because the chemical composition of Ti-6Al-2Sn-4Zr-2Mo is much closer to Ti-6Al-4V than that of γ-TiAl, thus requiring less convection for material changeover and then producing a narrower interface zone. The high brittleness of γ-TiAl led to the failed fabrication of Ti-6Al-4V/γ-TiAl under the fast-cooling SLM (without using baseplate pre-heating). In comparison, Ti-6Al-4V/Ti-6Al-2Sn-4Zr-2Mo was successfully built under the optimized condition. The successful manufacturing of Ti-6Al-2Sn-4Zr-2Mo also broadens the material palette of SLM.Laser remelting in the SLM chamber, rather than the expected wire electrical discharge machining (W-EDM), is concluded as the optimal treatment to improve the original casting surface. The growth of SLMed A357 on the remelted surface led to a defect-free and well-built interface. Laser remelting will also not add extra costs for future industrialization. In comparison, although the EDM exhibited optimality in decreasing the surface roughness, massive Al2O3 was induced at the same time by electrospark. The alumina was formed in large clusters, which decreased the wettability of the EDM surface to grow SLMed A357 and in consequence caused interfacial delamination.The established understandings on interface formation under the SLM processing could promote the development of multi-material SLM technologies. The successful multi-material cases also possess potentials in chemical (316L/Hastelloy X), aerospace (Ti-6Al-4V/Ti-6Al-2Sn-4Zr-2Mo) and automobile (cast A356/SLMed A357) applications.