Silica glass is a high-performance material used in many applications such as lenses, glassware, and fibers. However, modern additive manufacturing of micro-scale silica glass structures requires sintering of 3D-printed silica-nanoparticle-loaded composites at ~1200 °C, which causes substantial structural shrinkage and limits the choice of substrate materials. Here, 3D printing of solid silica glass with sub-micrometer resolution is demonstrated without the need of a sintering step. This is achieved by locally crosslinking hydrogen silsesquioxane to silica glass using nonlinear absorption of sub-picosecond laser pulses. The as-printed glass is optically transparent but shows a high ratio of 4-membered silicon-oxygen rings and photoluminescence. Optional annealing at 900 °C makes the glass indistinguishable from fused silica. The utility of the approach is demonstrated by 3D printing an optical microtoroid resonator, a luminescence source, and a suspended plate on an optical-fiber tip. This approach enables promising applications in fields such as photonics, medicine, and quantum-optics.
The topic of durable coloration and passivation of metal surfaces using state-of-theart techniques has gained enormous attention and devotion with unremitting efforts of researchers worldwide. Although femtosecond laser marking has been performed on many metals, the related coloration mechanisms are mainly referred to structural colors produced by the interaction of visible light with periodic surface structures. Yet, general quantitative determination of the resulting colors and their origins remain elusive. In this work, we realized quantitative separations of structural colors and compositional pigmentary colors on 301LN austenitic stainless steel surfaces that were treated by femtosecond laser machining. The overall color information was extracted from surface reflectance, with structural color given by numerical simulations, and oxide compositions by chemical state analysis. It was shown that the laser-induced apparent colors of 301LN steel surfaces were combinations of structural and compositional colorations, with the former dominating the angular response and the latter setting up the brownish bases. In addition to the quantification of colors, the analysis method in this work may be useful for the generation and specification of tailored color palettes for practical coloration on metal surfaces by femtosecond laser marking.
Abstract-Through silicon vias (TSVs) are key enablers of 3D integration technologies which, by vertically stacking and interconnecting multiple chips, achieve higher performances, lower power and a smaller footprint. Copper is the most commonly used conductor to fill TSVs; however, copper has a high thermal expansion mismatch in relation to the silicon substrate. This mismatch results in a large accumulation of thermomechanical stress when TSVs are exposed to high temperatures and/or temperature cycles, potentially resulting in device failure.In this paper, we demonstrate 300 µm long, 7:1 aspect ratio TSVs with Invar as a conductive material. The entire TSV structure can withstand at least 100 thermal cycles from -50• C to 190• C and at least one hour at 365 • C, limited by the experimental setup. This is possible thanks to matching coefficients of thermal expansion (CTE) of the Invar via conductor and of silicon substrate. This results in thermomechanical stresses that are one order of magnitude smaller compared to copper TSV structures with identical geometries, according to finite element modelling. Our TSV structures are thus a promising approach enabling 2.5D and 3D integration platforms for high-temperature and harsh-environment applications.
Through silicon vias (TSVs) are used e.g. to create electrical connections through MEMS wafers or through silicon interposers used in 2.5D packaging. Currently available technologies do not address situations in which TSVs through unthinned wafers have to withstand large temperature variations. We propose using ferromagnetic Invar metal alloy for this purpose due to its low mismatch in heat induced strain in comparison to silicon. We demonstrate the suitability of a magnetic assembly process for Invar TSV fabrication and the use of spin-on glass as a TSV insulator. We demonstrate TSVs, with contact pads, that tolerate temperature cycling between -50 °C and 190 °C and can withstand elevated temperatures of at least up to 365 °C.
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