| 1. |
- Huang, Po-Han, et al.
(författare)
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Three-dimensional printing of silica glass with sub-micrometer resolution
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
- Asiatici, Mikhail, et al.
(författare)
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Through Silicon Vias With Invar Metal Conductor for High-Temperature Applications
- 2017
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Ingår i: Journal of microelectromechanical systems. - : IEEE Press. - 1057-7157 .- 1941-0158. ; 26:1, s. 158-168
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Tidskriftsartikel (refereegranskat)abstract
- Through silicon vias (TSVs) are key enablers of 3-D integration technologies which, by vertically stacking andinterconnecting multiple chips, achieve higher performances,lower power, and a smaller footprint. Copper is the mostcommonly used conductor to fill TSVs; however, copper hasa high thermal expansion mismatch in relation to the siliconsubstrate. This mismatch results in a large accumulation ofthermomechanical stress when TSVs are exposed to high temperaturesand/or temperature cycles, potentially resulting in devicefailure. In this paper, we demonstrate 300 μm long, 7:1 aspectratio TSVs with Invar as a conductive material. The entireTSV structure can withstand at least 100 thermal cycles from −50 °C to 190 °C and at least 1 h at 365 °C, limited bythe experimental setup. This is possible thanks to matchingcoefficients of thermal expansion of the Invar via conductor andof silicon substrate. This results in thermomechanical stressesthat are one order of magnitude smaller compared to copperTSV structures with identical geometries, according to finiteelement modeling. Our TSV structures are thus a promisingapproach enabling 2.5-D and 3-D integration platforms for hightemperatureand harsh-environment applications.
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| 4. |
- Huang, Po-Han, et al.
(författare)
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3d Printing of Silica-HSQ Composites with Sub-Micrometer Resolution and Selectively Generated Silicon Nanocrystals
- 2023
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Ingår i: 2023 22nd International Conference on Solid-State Sensors, Actuators and Microsystems, Transducers 2023. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 433-436
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Laakso, Miku, 1989-, et al.
(författare)
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Maskless Manufacturing of Through Glass Vias (TGVs) and Their Test Structures
- 2017
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Ingår i: Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS). - 9781509050789 ; , s. 753-756
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Laakso, Miku, 1989-
(författare)
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Microfabrication and Integration Using Sub-Picosecond Laser Pulses and Magnetic Assembly
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Laakso, Miku, 1989-, et al.
(författare)
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Through-Glass Vias for MEMS Packaging
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 8. |
- Laakso, Miku, 1989-, et al.
(författare)
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Water in contact with the backside of a silicon substrate enables drilling of high-quality holes through the substrate using ultrashort laser pulses
- 2020
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 28:2, s. 1394-1408
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Laakso, Miku, 1989-, et al.
(författare)
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Wide temperature range through silicon vias made of Invar and spin-on glass for interposers and MEMS
- 2016
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Ingår i: 2016 IEEE 29th International Conference on Micro Electro Mechanical Systems (Mems). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509019731 ; , s. 585-588
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Konferensbidrag (refereegranskat)abstract
- 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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| 10. |
- Ribet, Federico, et al.
(författare)
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Vertical integration of microchips by magnetic assembly and edge wire bonding
- 2020
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Ingår i: MICROSYSTEMS & NANOENGINEERING. - : NATURE PUBLISHING GROUP. - 2055-7434. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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