Silica glass is a high-performance material that has become essential in modern life. Functionalization of silica glass is critically important for its optical applications such as in lenses and filters, which is however challenging to realize and manipulate in 3D-printed silica glass. Here, we report 3D printing of solid composites of silica glass and hydrogen silsesquioxane (HSQ) with sub-micrometer resolution. This is achieved by encapsulating HSQ inside silica glass by selectively transforming HSQ to silica glass by multi-photon absorption using a femtosecond laser. Furthermore, we demonstrated selective generation of photoluminescent silicon nanocrystals in the HSQ regions inside the composites by annealing. This is based on our experimental observation that the silica glass transformed from HSQ by multi-photon absorption, unlike HSQ, does not generate silicon nanocrystals upon annealing.

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 similar to 1200 degrees 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 degrees 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.

Microfabricated devices and systems have many exciting applications such as accelerometers for triggering the launching of airbags in cars, gyroscopes for sensing the rotations of mobile phones, and micromirror arrays for controlling light reflection in digital light projectors. These devices are currently produced using semiconductor manufacturing techniques, which are suitable for large volumes of mostly planar structures. However, they have limited economic viability for products with lower volumes, and they also constrain the three-dimensional (3D) structuring of the microdevices. Therefore, there is a need for new manufacturing techniques that are economically viable even for smaller volumes and allow truly 3D microdevice designs. To address this problem, this thesis presents developments in microfabrication and integration using two main methods: (1) The usage of sub-picosecond laser pulses for locally adding and modifying material and (2) the usage of an external magnetic field to handle fragile micrometric objects in order to assemble them into their target locations. These two methods are used for six main applications out of which four involve packaging and integrating microsystems, one involves the manufacturing of 3D microstructures, and one involves directly patterning microstructures on a surface.

A key technology in the packaging and integration of microsystems, and a focus area of this thesis, is the manufacturing of through-substrate vias. They are used as electrical interconnections through device and package substrates. They allow smaller packages, which is a requirement, for example, for the Internet of Things where different types of microsensors and actuators are placed in our everyday environment. The first application related to the manufacturing of through-substrate vias is laser drilling of through-silicon holes. Laser drilling allows holes to be created where traditional etching methods might be uneconomical or unpractical. Laser drilling also allows the drilling of tilted holes, which can improve the radio-frequency performance of the vias. The second application is the magnetic assembly of metal conductors into holes in a glass substrate. Glass substrates have several benefits over silicon substrates, such as lower radio-frequency losses, but the production of through-glass vias is challenging due to the difficulty of creating regular holes through the glass. The magnetic assembly allows metal conductors to be placed into the holes in glass independent of the hole shape. This could lead to wider use of glass with its excellent properties as a packaging substrate for microsystems. The third application is through-substrate vias for high-temperature environments. These vias are manufactured by magnetically assembling metal conductors with low thermal expansion into holes in a silicon substrate. The low thermal expansion leads to reduced stresses at elevated temperatures. This could allow using through-substrate vias to reduce package sizes even in demanding high-temperature environments found, for example, in the space industry.

The fourth and last application related to the packaging and integrating microsystems is the vertical assembly of microchips using an external magnetic field. Microsystem fabrication is focused on in-plane structures, but some applications require or would benefit from out-of-plane structures. Examples of such applications are a biosensor placed inside a microneedle inserted into tissue or flow sensors bending in the flow. Manufacturing the out-of-plane structures on the same substrate with other structures requires complicated manufacturing techniques and occupies a large surface area. When using the vertical assembly process, the out-of-plane structures can be manufactured on a separate substrate using standard microfabrication techniques, and the out-of-plane structures can then be assembled afterward in a vertical orientation on a receiving substrate.

Manufacturing of 3D microstructures is not trivial using the standard micromanufacturing techniques. Free-form 3D printing of submicrometric features is possible using two-photon polymerization, but the material properties of polymers are not comparable to those of silica glass. This thesis demonstrates 3D printing of silica glass with submicrometric features using sub-picosecond laser pulses. This new 3D freedom in micromanufacturing could be used, for example, in building more complicated micro-opto-electro-mechanical systems.

Directly patterning microstructures on a surface is possible by exposing the surface to laser pulses. These structures can affect the optical and wetting properties of the surfaces. More specifically, periodic ripple structures can act as diffraction gratings, altering the optical reflection properties of the surface. Exposure to sub-picosecond laser pulses can also cause chemical changes on the surface, and these changes can potentially affect the reflection properties. This thesis demonstrates that the chemical changes indeed affect the reflection properties, and this information could be used when manufacturing ripple patterns, for example, for security markings or for decorative use.

Enheter och system i mikroformat har många spännande applikationer, såsom accelerometrar för att utlösa krockkuddar i bilar, gyroskop för att avkänna rotation hos mobiltelefoner och matriser av mikrospeglar för att kontrollera ljusreflektion i digitala projektorer. Dessa anordningar framställs för närvarande med tillverkningstekniker för halvledare, som är lämpliga för stora volymer av mestadels plana strukturer. Dessa tekniker är emellertid inte kostnadseffektiva för produkter med lägre volymer och begränsar den tredimensionella (3D) struktureringen av mikroenheter. Därför finns det ett behov av nya tillverkningstekniker som är lönsamma även för mindre volymer och som verkligen möjliggör 3D strukturering av mikroenheter. För att hantera detta problem presenterar denna avhandling utveckling inom mikrofabrikation och integration med hjälp av två huvudmetoder: (1) Användning av laserpulser kortare än en pikosekund för att lägga till och modifiera material och (2) användningen av ett yttre magnetfält för att hantering av ömtåliga mikrometerstora föremål för att montera dem på deras måldestinationer. Dessa två metoder används, i denna avhandling, för sex huvudapplikationer, varav fyra involverar förpackning och integrering av mikrosystem, en involverar tillverkning av 3D-mikrostrukturer och en involverar direkt mönstrade mikrostrukturer på en yta.

Ett viktigt teknologiområde inom förpackning och integration av mikrosystem, samt ett huvudområde i denna avhandling, är tillverkningen av elektriska anslutningar genom olika substrat. De används som elektriska sammankopplingar genom komponenter och substrat. De möjliggör mindre komponenter, vilket är ett krav, till exempel för ”Sakernas Internet” (”Internet of Things”) där olika typer av mikrosensorer och aktuatorer placeras i vår omgivning. Den första tillämpningen relaterad till tillverkning av substratgenomföringar är laserborrning av genomgående hål i kiselsubstrat. Laserborrning gör det möjligt att framställa hål där traditionella etsningsmetoder kan vara oekonomiska eller opraktiska. Laserborrning tillåter också framställning av vinklade hål, vilket kan förbättra elektriska genomföringars radiofrekvensprestanda. Den andra tillämpningen rör magnetisk montering av metalledare i hål i ett glassubstrat. Glassubstrat har flera materialegenskaper som är bättre jämfört med kiselsubstrat, exempelvis lägre radiofrekvensförluster, men framställning av genomföringar i glas är utmanande på grund av svårigheten att skapa väldefinierade hål i glas. Med hjälp av magnet-baserad montering kan metalledare placeras i hål oberoende av hålens kvalitet i glassubstratet. Denna metod kan leda till en bredare användning av glassubstratet, med deras utmärkta egenskaper, inom paketering av mikrosystem. Den tredje tillämpningen, som beskrivs i denna avhandling, är substratgenomföringar för användning vid höga temperaturer. Dessa tillverkas genom magnetisk montering av metalledare med låg termisk expansionbenägenhet i hål i kiselsubstrat. Dessa kiselgenomföringar har visats kunna minska de mekaniska spänningarna vid höga temperaturer. Detta skulle möjliggöra användning av substratgenomföringar för att minska komponentförpackningar även för mycket krävande högtemperaturmiljöer, som till exempel inom rymdindustrin.

Den fjärde och sista applikationen relaterad till förpackning och integration av mikrosystem rör vertikal sammansättning av mikrochips med hjälp av ett yttre magnetfält. Tillverkning av mikrosystem är normalt inriktade på plana strukturer, men vissa tillämpningar kräver strukturer utanför komponentens huvudsakliga plan. Exempel på sådana tillämpningar är en biosensor placerad i en mikronål införd i vävnad eller flödessensorer som böjer sig i ett flöde. Tillverkning av vertikala konstruktioner från samma substrat med plana strukturer kräver komplicerade tillverkningstekniker och tar stor yta från mikrochips. Genom att vertikalt sammanföra olika delar kan konstruktioner utanför planet tillverkas på ett separat substrat med hjälp av standardmikrofabrikationstekniker och sedan monteras vertikalt till ett annat substrat med plana strukturer.

Det är inte trivialt att tillverka 3D-mikrostrukturer med hjälp av standardmikrofabrikationstekniker. Med en alternativ metod så kan mikrostrukturer ”3D-printas” med hjälp av tvåfotonpolymerisationsteknik, men polymerers materialegenskaper är i många avseenden sämre än många icke-organiska material. Denna avhandling visar hur strukturer i kiseldioxidglas med goda optiska egenskaper kan ”3D-printas” med strukturer mindre än en mikrometer med hjälp av laserpulser kortare än en pikosekund. Denna nya 3D-frihet vid mikrofabrikation kan till exempel användas för att bygga avancerade mikro-opto-elektromekaniska system.

Det är möjligt att direkt mönstra mikrostrukturer på en yta genom att utsätta ytan för laserpulser. Dessa strukturer kan påverka ytans optiska egenskaper och vätningsegenskaper. Mer specifikt kan periodiska vågmönster fungera som diffraktionsgitter som förändrar ytans optiska reflektionsegenskaper. Exponering för laserpulser kortare än en pikosekund kan också orsaka kemiska förändringar på ytan, och dessa förändringar kan potentiellt påverka reflektionsegenskaperna. Denna avhandling visar hur man genom exponering med laserpulser kortare än en pikosekund kan orsaka kemiska ytförändringar på ytan och hur dessa förändringar påverkar de optiska reflektionsegenskaperna. Denna teknik kan användas för tillverkning av vågmönster, till exempel för säkerhetsmarkeringar eller för dekorativ användning.

The out-of-plane integration of microfabricated planar microchips into functional three-dimensional (3D) devices is a challenge in various emerging MEMS applications such as advanced biosensors and flow sensors. However, no conventional approach currently provides a versatile solution to vertically assemble sensitive or fragile microchips into a separate receiving substrate and to create electrical connections. In this study, we present a method to realize vertical magnetic-field-assisted assembly of discrete silicon microchips into a target receiving substrate and subsequent electrical contacting of the microchips by edge wire bonding, to create interconnections between the receiving substrate and the vertically oriented microchips. Vertical assembly is achieved by combining carefully designed microchip geometries for shape matching and striped patterns of the ferromagnetic material (nickel) on the backside of the microchips, enabling controlled vertical lifting directionality independently of the microchip's aspect ratio. To form electrical connections between the receiving substrate and a vertically assembled microchip, featuring standard metallic contact electrodes only on its frontside, an edge wire bonding process was developed to realize ball bonds on the top sidewall of the vertically placed microchip. The top sidewall features silicon trenches in correspondence to the frontside electrodes, which induce deformation of the free air balls and result in both mechanical ball bond fixation and around-the-edge metallic connections. The edge wire bonds are realized at room temperature and show minimal contact resistance (<0.2 Omega) and excellent mechanical robustness (>168mN in pull tests). In our approach, the microchips and the receiving substrate are independently manufactured using standard silicon micromachining processes and materials, with a subsequent heterogeneous integration of the components. Thus, this integration technology potentially enables emerging MEMS applications that require 3D out-of-plane assembly of microchips.

Holes through silicon substrates are used in silicon microsystems, for example in vertical electrical interconnects. In comparison to deep reactive ion etching, laser drilling is a versatile method for forming these holes, but laser drilling suffers from poor hole quality. In this article, water is used in the silicon drilling process to remove debris and the shape deformations of the holes. Water is introduced into the drilling process through the backside of the substrate to minimize negative effects to the drilling process. Drilling of inclined holes is also demonstrated. The inclined holes could find applications in radio frequency devices.

The topic of durable coloration and passivation of metal surfaces using state-of-the-art 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.

A through-glass via (TGV) provides a vertical electrical connection through a glass substrate. TGVs are used in advanced packaging solutions, such as glass interposers and wafer-level packaging of microelectromechanical systems (MEMS). However, TGVs are challenging to realize because via holes in glass typically do not have a sufficiently high-quality sidewall profile for super-conformal electroplating of metal into the via holes. To overcome this problem, we demonstrate here that the via holes can instead be filled by magnetically assembling metal wires into them. This method was used to produce TGVs with a typical resistance of 64 m Omega, which is comparable with other metal TGV types reported in the literature. In contrast to many TGV designs with a hollow center, the proposed TGVs can be more area efficient by allowing solder bump placement directly on top of the TGVs, which was demonstrated here using solder-paste jetting. The magnetic assembly process can be parallelized using an assembly robot, which was found to provide an opportunity for increased wafer-scale assembly speed. The aforementioned qualities of the magnetically assembled TGVs allow the realization of glass interposers and MEMS packages in different thicknesses without the drawbacks associated with the current TGV fabrication methods.

Novelty / Progress Claims We have developed a new method for fabrication of through-glass vias (TGVs). The method allows rapid filling of via holes with metal rods both in thin and thick glass substrates.

Background Vertical electrical feedthroughs in glass substrates, i.e. TGVs, are often required in wafer-scale packaging of MEMS that utilizes glass lids. The current methods of making TGVs have drawbacks that prevent the full utilization of the excellent properties of glass as a package material, e.g. low RF losses. Magnetic assembly has been used earlier to fabricate through-silicon vias (TSVs), and in this work we extend this method to realize TGVs [1].

Methods The entire TGV fabrication process is maskless, and the processes used include: direct patterning of wafer metallization using femtosecond laser ablation, magnetic-fieldassisted self-assembly of metal wires into via holes, and solder-paste jetting of bump bonds on TGVs.

Results We demonstrate that: (1) the magnetically assembled TGVs have a low resistance, which makes them suitable even for low-loss and high-current applications; (2) the magneticassembly process can be parallelized in order to increase the wafer-scale fabrication speed; (3) the magnetic assembly produces void-free metal filling for TGVs, which allows solder placement directly on top of the TGV for the purpose of high integration density; and (4) good thermal-expansion compatibility between TGV metals and glass substrates is possible with the right choice of materials, and several suitable metals-glass pairs are identified for possible improvement of package reliability [2].

[1] M. Laakso et al., IEEE 30th Int. Conf. on MEMS, 2017. DOI:10.1109/MEMSYS.2017.7863517

[2] M. Laakso et al., “Through-Glass Vias for Glass Interposers and MEMS Packaging Utilizing Magnetic Assembly of Microscale Metal Wires,” manuscript in preparatio

Through glass vias (TGVs) are a key component in glass-based interposers and microelectromechanical-system lid wafers. Magnetic-field-assisted self-assembly has been demonstrated earlier in fabrication of through silicon vias. Here we present an entirely maskless TGV fabrication process utilizing magnetic assembly. Femtosecond laser is used for ablative direct patterning of surface metal layers and for exposing the TGV conductors after wafer thinning. The proposed TGV structure is shown to be electrically functional by measuring the TGV resistance values.