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Microfabrication and Integration Using Sub-Picosecond Laser Pulses and Magnetic Assembly
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Micro and Nanosystems.ORCID iD: 0000-0003-1112-3308
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

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.

Place, publisher, year, edition, pages
Stockholm, Sweden: Kungliga tekniska högskolan, 2020. , p. 83
Series
TRITA-EECS-AVL ; 2020:10
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-269539ISBN: 978-91-7873-430-6 (print)OAI: oai:DiVA.org:kth-269539DiVA, id: diva2:1413030
Public defence
2020-04-03, https://kth-se.zoom.us/j/723570718, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-09 Last updated: 2020-03-26Bibliographically approved
List of papers
1. Through Silicon Vias With Invar Metal Conductor for High-Temperature Applications
Open this publication in new window or tab >>Through Silicon Vias With Invar Metal Conductor for High-Temperature Applications
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2017 (English)In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 26, no 1, p. 158-168Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE Press, 2017
Keywords
TSV, CTE, 3D packaging, FEM, spin-on glass, thermal reliability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-200917 (URN)10.1109/JMEMS.2016.2624423 (DOI)000397049500016 ()2-s2.0-84996848937 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, WOV - Working on VenusVINNOVA, 324189Swedish Foundation for Strategic Research , GMT14-0071EU, European Research Council, 277879
Note

QC 20170207

Available from: 2017-02-06 Created: 2017-02-05 Last updated: 2020-03-10Bibliographically approved
2. Through-Glass Vias for Glass Interposers and MEMS Packaging Applications Fabricated Using Magnetic Assembly of Microscale Metal Wires
Open this publication in new window or tab >>Through-Glass Vias for Glass Interposers and MEMS Packaging Applications Fabricated Using Magnetic Assembly of Microscale Metal Wires
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2018 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 44306-44317Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2018
Keywords
Chip scale packaging, femtosecond laser, glass interposer, laser ablation, multichip modules, robotic assembly, self-assembly, spin-on glass, thermal expansion, through-glass via, through-silicon vias, TSV
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-235465 (URN)10.1109/ACCESS.2018.2861886 (DOI)000444505800001 ()2-s2.0-85050982480 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationVINNOVA, 324189Swedish Foundation for Strategic Research , GMT14-0071 RIF14-0017
Note

QC 20180928

Available from: 2018-09-28 Created: 2018-09-28 Last updated: 2020-03-10Bibliographically approved
3. Corrigendum to "Quantitative assessment of structural and compositional colors induced by femtosecond laser: A case study on 301LN stainless steel surface" [Appl. Surf. Sci. 484 (2019) 655-662]
Open this publication in new window or tab >>Corrigendum to "Quantitative assessment of structural and compositional colors induced by femtosecond laser: A case study on 301LN stainless steel surface" [Appl. Surf. Sci. 484 (2019) 655-662]
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2020 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 504, article id 144583Article in journal (Other academic) Published
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-269418 (URN)10.1016/j.apsusc.2019.144583 (DOI)000502040600167 ()2-s2.0-85075485321 (Scopus ID)
Note

QC 20200313

Available from: 2020-03-06 Created: 2020-03-06 Last updated: 2020-03-13Bibliographically approved
4. Quantitative assessment of structural and compositional colors induced by femtosecond laser: A case study on 301LN stainless steel surface
Open this publication in new window or tab >>Quantitative assessment of structural and compositional colors induced by femtosecond laser: A case study on 301LN stainless steel surface
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2019 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 484, p. 655-662Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier B.V., 2019
Keywords
Compositional color, Femtosecond laser marking, Laser coloration, Structural color, Chemical analysis, Femtosecond lasers, Marking machines, Microalloyed steel, Structural metals, Chemical state analysis, Femtosecond laser machining, Periodic surface structures, Quantitative assessments, Quantitative determinations, Quantitative separation, State-of-the-art techniques, Color
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-252501 (URN)10.1016/j.apsusc.2019.04.147 (DOI)000471830700072 ()2-s2.0-85064510118 (Scopus ID)
Note

Correction in DOI:10.1016/j.apsusc.2019.144583 ISI:000502040600167

QC 20190711. QC 20200115

Available from: 2019-07-11 Created: 2019-07-11 Last updated: 2020-03-10Bibliographically approved
5. Water in contact with the backside of a silicon substrate enables drilling of high-quality holes through the substrate using ultrashort laser pulses
Open this publication in new window or tab >>Water in contact with the backside of a silicon substrate enables drilling of high-quality holes through the substrate using ultrashort laser pulses
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2020 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 28, no 2, p. 1394-1408Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Optical Society of America, 2020
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-267818 (URN)10.1364/OE.377256 (DOI)000513232200048 ()2-s2.0-85078512474 (Scopus ID)
Note

QC 20200227

Available from: 2020-02-27 Created: 2020-02-27 Last updated: 2020-03-16Bibliographically approved
6. Vertical Integration of Microchips by Magnetic Assembly and Edge Wire Bonding
Open this publication in new window or tab >>Vertical Integration of Microchips by Magnetic Assembly and Edge Wire Bonding
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(English)In: Article in journal (Refereed) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-259159 (URN)
Note

QC 20191113

Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2020-03-10Bibliographically approved
7. Three-dimensional printing of silica-glass structures with submicrometric features
Open this publication in new window or tab >>Three-dimensional printing of silica-glass structures with submicrometric features
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-269423 (URN)
Note

QC 20200313

Available from: 2020-03-06 Created: 2020-03-06 Last updated: 2020-03-13Bibliographically approved

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