3D printing at the macroscale has evolved from making plastic prototypes to the production of high-performance functional metal parts for industries such as medical and aerospace. By contrast, MEMS devices today are produced in large quantities using semiconductor manufacturing processes. However, the semiconductor manufacturing paradigm is not cost-effective for producing customized MEMS devices in small to medium volumes (tens to thousands of units per year), and related applications are difficult to address efficiently. 3D printing of functional MEMS devices could play an important role in filling this gap. Here, we discuss recent advances in 3D- printed functional MEMS, addressing the challenges of economical customization at smaller production volumes.

Interest in carbon dioxide (CO2) sensors is growing rapidly due to the increasing awareness of the link between air quality and health. Indoor, high CO2 levels signal poor ventilation, and outdoor the burning of fossil fuels and its associated pollution. CO2 gas sensors based on integrated optical waveguides are a promising solution due to their excellent gas sensing selectivity, compact size, and potential for mass manufacturing large volumes at low cost. However, previous demonstrations have not shown adequate performance for atmospheric-level sensing on a scalable platform. Here, we report the clearly resolved detection of 500 ppm CO2 gas at 1 s integration time and an extrapolated 1σ detection limit of 73 ppm at 61 s integration time using an integrated suspended silicon waveguide at a wavelength of 4.2 µm. Our waveguide design enables suspended strip waveguides with bottom anchors while maintaining a constant waveguide core cross-sectional geometry. This unique design results in a low propagation loss of 2.20 dB/cm. The waveguides were implemented in a 150 mm silicon on insulator (SOI) platform using standard optical lithography, providing a clear path to low-cost mass manufacturing. The low CO2 detection limit of our proposed waveguide, combined with its compatibility for high-volume production, creates substantial opportunities for waveguide sensing technology in CO2 sensing applications such as fossil fuel combustion monitoring and indoor air quality monitoring for ventilation and air conditioning systems.

Utilizing lanthanide upconversion nanoparticles to convert near-infrared to visible light presents a potential way for fabricating the next generation of low-cost near-infrared imaging sensors. Integrating microlens arrays with upconversion nanoparticles has been shown to be a promising approach for improving the efficiency of upconversion nanoparticles. However, approaches suitable for prototyping and producing microlens arrays to explore optimal device designs are lacking. In this work, we report an approach to fabricating flexible near-infrared-to-visible upconversion devices incorporating upconversion nanoparticles and microlens arrays, which enables easy adjustment of device structures and lens geometry. This is achieved by fabricating flexible films containing upconversion nanoparticles using molding in combination with femtosecond laser 3D printing of lenses, facilitating rapid prototyping for different application scenarios. By adding the microlens array, the intensities of the green (525 and 540 nm) and red (654 nm) upconversion emission bands were enhanced by a factor of 3 and 10, respectively, potentially leading to much reduced detectable near-infrared light intensity.

Integration of functional materials and structures on the tips of optical fibers has enabled various applications in micro-optics, such as sensing, imaging, and optical trapping. Direct laser writing is a 3D printing technology that holds promise for fabricating advanced micro-optical structures on fiber tips. To date, material selection has been limited to organic polymer-based photoresists because existing methods for 3D direct laser writing of inorganic materials involve high-temperature processing that is not compatible with optical fibers. However, organic polymers do not feature stability and transparency comparable to those of inorganic glasses. Herein, we demonstrate 3D direct laser writing of inorganic glass with a subwavelength resolution on optical fiber tips. We show two distinct printing modes that enable the printing of solid silica glass structures (“Uniform Mode”) and self-organized subwavelength gratings (“Nanograting Mode”), respectively. We illustrate the utility of our approach by printing two functional devices: (1) a refractive index sensor that can measure the indices of binary mixtures of acetone and methanol at near-infrared wavelengths and (2) a compact polarization beam splitter for polarization control and beam steering in an all-in-fiber system. By combining the superior material properties of glass with the plug-and-play nature of optical fibers, this approach enables promising applications in fields such as fiber sensing, optical microelectromechanical systems (MEMS), and quantum photonics.

We demonstrate methane gas sensing using suspended silicon waveguides and experimentally validate the sensitivity optimization of waveguide-based gas sensors by varying waveguide lengths. This method enables application-optimized integrated optical gas sensors.

We demonstrate methane gas sensing using suspended silicon waveguides and experimentally validate the sensitivity optimization of waveguide-based gas sensors by varying waveguide lengths. This method enables application-optimized integrated optical gas sensors.

Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4 cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160 V at an ultrahigh scan rate up to 30 V s−1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150 V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.

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.

3D printing by two-photon polymerization (TPP) is a well-established manufacturing approach for realizing 3D polymer structures at the micro- and nanoscale. However, an important shortcoming of 3D printing by two-photon polymerization is that it is extremely challenging to print 3D objects with long overhanging features, which severely limits the application space of this technology. Here, we introduce a methodology for 3D printing by two-photon polymerization that allows the realization of 3D objects with long overhanging structures that cannot be printed using conventional printing strategies. Our methodology combines different printing approaches for realizing the overhanging structure, including locally adjusted printing block sizes and a mix of the Shell & Scaffold and Solid printing modes. As a result, objects with long overhanging parts can be printed without the need for added support structures. Using this approach, we demonstrate successful printing of overhanging cantilevers with a quadratic cross-section of 50 µm x 50 µm and lengths of up to 1000 µm. Thus, our printing modality substantially extends the capabilities and application space of 3D printing by two-photon polymerization and removes current design limitations regarding 3D printed objects with long overhanging structures.

Femtosecond laser-based fabrication technologies have seen rapid developments in the past decades, thanks to the capability of femtosecond lasers to induce localized multiphoton absorption in materials. Multiphoton absorption can result in various material modifications that can be leveraged for additive and subtractive manufacturing. Their versatile applications have demonstrated the great potential of femtosecond lasers in advancing micro- and nano-fabrication. These include (1) multiphoton crosslinking enabling 3D printing with unprecedented patterning freedom and sub-micrometer resolution,(2) the formation of self-organized structures enabling the creation of multi-functional sub-wavelength patterns in solid materials, and (3) multiphoton ablation enabling precise sculpturing of wide-ranging materials. Nevertheless, there remains a large room to explore when it comes to available materials and achievable devices. This thesis aims to advance the applications of femtosecond lasers to glasses and 2D materials for the fabrication of advanced and integrated microdevices for photonics and energy storage. The first part of this thesis presents two approaches for 3D printing of inorganic glass. These approaches are based on two unusual observations in hydrogen silsesquioxane (HSQ) upon femtosecond laser exposure: (1) multiphoton crosslinking and (2) the formation of self-organized structures. The first work reports an approach for 3D printing of solid silica glass with sub-micrometer resolution by multiphoton crosslinking of HSQ. In contrast to the alternative methods, our approach does not require any thermal treatments, which offers desirable design fidelity and integration flexibility. The second work reports the possibility of inducing material modifications (1) and (2) in HSQ simultaneously. This possibility enables additive manufacturing of self-organized nanogratings, and thus, 3D printing of hierarchical structures made of Si-rich glass. In the third work, a protocol to perform the 3D printing on optical fiber tips is developed, which enables the fabrication of fiber-tip optical microdevices for sensing and beam shaping. The second part of this thesis presents the application of femtosecond lasers to fabricating on-paper microsupercapacitors (MSCs).MSCs are promising energy-storage microdevices for self-powering electronics, and paper substrates, yet vulnerable, are attractive for their sustainability and flexibility. The material and shape of MSCelectrodes play a crucial role in the energy-storage performance, and 2D materials have emerged as suitable candidate materials. In the last two works, a scalable approach for the precise micromachining of 2D-material electrodes by multiphoton ablation is developed, preserving their electrochemical performance and the integrity of the paper substrates.

Femtosekundlaser-baserade tillverkningsteknologier har genomgått snabb utveckling de senaste årtiondena tack vare femtosekundlasrars förmåga att inducera lokal multifotonabsorption i material. Multifotonabsorption kan resultera i olika typer av materialförändringar som kan utnyttjas för additiv och subtraktiv tillverkning. De mångsidiga tillämpningarna visar på potentialen av femtosekundslasrar för mikro- och nanotillverkning. Dessa inkluderar (1) multifotonkorslänkning för 3D-utskrift med mönsterfrihet och submikrometerupplösning, (2) bildandet av självorganiserade strukturer för multifunktionella subvåglängdsmönster i fasta material och (3) multifotonablation för precisionsformning av flertalet material. Trots detta finns det utrymme för att utforska möjliga material och realiserbara produkter. Denna avhandling syftar till att utöka användningsområdet för femtosekundlasrar till tillverkning av avancerade komponenter utav såväl glas som 2D material, för användning inom fotonik och energilagring. Den första delen av denna avhandling presenterar två tillvägagångssätt för 3D-utskrift av oorganiskt glas. Dessa baseras på materialmodifieringar i vätesilseskvioxan (HSQ) vid exponering för femtosekundslaserstrålning: (1) multifoton-korslänkning och (2) bildandet av självorganiserade strukturer. Det första arbetet redovisar kring 3D-utskrift av fast kiseldioxidglas med submikrometerupplösning genom multifoton-korslänkning av HSQ. Vår metod kräver ingen termisk behandling, vilket ger leder till god överensstämmelse mellan ritning och produkt och ger flexibilitet kring integration. Det andra arbetet redogör för möjligheten att inducera materialmodifieringarna (1) och (2) i HSQ samtidigt, vilket möjliggör additiv tillverkning av självorganiserade nanogitter och 3D-utskrift av hierarkiska strukturer av kiselrikt glas. Det tredje arbetet är en utveckling av ett protokoll för 3D-utskrift på ändarna av optiska fiberkablar för tillverkning av optiska mikroenheter som sensorer och strålformare. Den andra delen av denna avhandling presenterar användningen av femtosekundslasrar för tillverkning av mikrosuperkondensatorer (MSCs) på papper. MSCs har fått stor uppmärksamhet som lovande energilagringsmikroenheter för självdriven elektronik. Papperssubstrat är även attraktiva för sin hållbarhet och flexibilitet. 2D-material har relevanta elektrokemiska egenskaper för MSC-elektroder och elektrodernas form påverkar deras prestanda. I de två sista arbetena utvecklas en metod för mikromaskintillverkning av elektroder utav 2D-material genom multifotonablation, vilket bevarar deras elektrokemiska prestanda och de fysiska egenskaperna av papperssubstraten.