New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

Ultra precision physical micro-machining for integrated optics

This study looks at the application of physical micromachining techniques to integrated optics. These physical micromachining techniques were used to make structures which would be difficult or impossible to produce using conventional cleanroom based technologies.A tuneable Bragg grating was fabricated and characterized and was found to offer an enhanced power efficiency for tuning of 45 pm/mW for the transverse magnetic mode and 39 pm/mW for the transverse electric mode. This an improvement in the operating power efficiency of a factor of 90 over bulk thermally tuned Bragg gratings in silica.A dual cantilever device has also been demonstrated which can operate as a force sensor or variable attenuator. The response of the device to mechanical actuation was measured, and shown to be very well described by conventional fibre optic angular misalignment theory. The device has the potential to be utilized within integrated optical components for sensors or attenuators. An array of devices was fabricated with potential for parallel operation. The fabrication work features the first use of a dicing saw in plunge cutting mode to rapidly produce grooves which were free of chipping.A wire electro discharge unit was designed and built. This was retrofitted to a micromill to give capability to manufacture tools directly on machine. This work built upon previous machining research in the group to allow free form diamond tools to be fabricated. Tools formed by wire electro discharge machining of polycrystalline diamond were formed. A ring tool was created and proved to be able to machine ring structures in the ductile mode regime in germanium oxide glass with a surface roughness of Ra 4.9 nm. This is the first time that ductile mode machining has been achieved in glass with this type of tool. By using a XeF2 etch this was shown to be able to create the structures necessary for whispering gallery mode resonators. A number of exemplar micro disk structures have been researched in this work to test the concept and provide real examples. Firstly a phosphogermanate glass on silica resonator was fabricated. A germanium oxide glass disc was also fabricated using the silicon under-etch process.These trial optical devices have shown that physical machining provides a viable route for fabricating integrated optical elements

Advances in electronic packaging technologies by ultra-small microvias, super-fine interconnections and low loss polymer dielectrics

The fundamental motivation for this dissertation is to address the widening interconnect gap between integrated circuit (IC) demands and package substrates specifically for high frequency digital-RF systems applications. Moore's law for CMOS ICs predicts that transistor density on ICs will double approximately every 18 months. The current state-of-the-art in IC package substrates is at 20µm lines/spaces and 50-60µm microvia diameter using epoxy dielectrics with loss tangent above 0.01. The research targets are to overcome the barriers of current technologies and demonstrate a set of advanced materials and process technologies capable of 5-10µm lines and spaces, and 10-30µm diameter microvias in a multilayer 3-D wiring substrate using 10-25µm thin film dielectrics with loss tangent in the <0.005. The research elements are organized as follows with a clear focus on understanding and characterization of fundamental materials structure-processing-property relationships and interfaces to achieve the next generation targets. (a) Low CTE Core Substrate, (b) Low Loss Dielectrics with 25µm and smaller microvias, (c) Sub-10µm Width Cu Conductors, and (d) Integration of the various dielectric and conductor processes.Ph.D.Committee Chair: Tummala, Rao; Committee Member: Iyer, Mahadevan; Committee Member: Saxena, Ashok; Committee Member: Swaminathan, Madhavan; Committee Member: Wong, Chingpin

MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

Mm Scale 3d Silica Waveguide Fabrication Technique for Solar Energy Concentration Systems

The overreaching goal of this dissertation research is to achieve fabrication of mm scale waveguide structure for solar energy concentration systems. In the proposed design, a high concentrator photovoltaics (HCPV) with 1000x concentration and >90 % optical efficiency is targeted. The concept consists of three components: lens array, coupler and waveguiding section. Fused silica is assigned as the waveguide material, since it has a high optical transmission and low absorption and it provides the scalability and low manufacturing cost sought in the fabrication technique. To acquire the desired shape in waveguide, femtosecond laser irradiation followed by chemical etching (FLICE) process is used for fused silica light pipes fabrication. Among two widely used etchants potassium hydroxide (KOH) is preferred over hydrogen fluoride (HF) regarding its higher selectivity. FLICE process parameters have been optimized to achieve higher selectivity, higher manufacturing speed and better surface quality. The minimum number of overlapped pulses is reduced to 3.2 which corresponds to 1.25 m/s writing speed at given 2 MHz laser pulse repetition rate at given 2 μm spot size and an acceptable filtered surface roughness of 400 nm for 1 mm^2 area is achieved. The achieved minimum filtered surface roughness is scaled down to 21.8 nm for given 1 mm^2 area. Up to 1X5 staggered and tapered light pipes with up to 12.75x geometric concentration factor with a 45° angled input facet is successfully fabricated. The achieved accuracy of the angled surfaces is smaller than ±0.5° and ±0.01° for 45° and side wall tapered surfaces, respectively. Having evaluated the polishing techniques, CO2 laser polishing is decided to be employed in this study to obtain a smooth surface finish. Surface profiles are measured by atomic force microscopy (AFM) for generally high spatial frequency analysis and white light interferometry (WLI) for low spatial frequency analysis. Measurements demonstrate that the surface root mean square (RMS) roughness is decreased almost two order of magnitude. 95% transmission efficiency is measured for waveguide samples up to 50 mm in length and 1 mm^2 cross sectional area when the Fresnel losses are ignored and incident angles (in air) are averaged according to F/1.5 lens. Complex shapes in waveguides such as angled facets, tapering of the cross-section along the length, and combiners are proven to be possible to fabricate with high precision

Nanolithography on non-planar surfaces and self-assembly of metal salt-polymer nanomaterials

This thesis is focused on fabrication of high aspect ratio nanostructures on non-planar surfaces using evaporated electron beam resist (Part I), and a novel fabrication methods of high resolutionhigh-resolution surface nanostructures using metal salt: polymer nanocomposites self-assembly (Part II). Various top-down and bottom-up nanopatterning techniques are currently available with the rapid progress in instrumentation and material engineering. However, patterning on non-planar surfaces of various materials still remains an overwhelming challenge because the conventional resist coating method, spin-coating, works well for only planar surfaces such as a flat wafer. On the other hand, the ability to pattern any given surface at the nanoscale, in particular surfaces with high inherent roughness or with pre-patterned micro-scale features, opens new perspectives in various fields from multi-scale biomimetics to optoelectronics. Part I (Chapter 1-4) of the present thesis aims to address this issue using evaporated electron beam resist. Electron beam lithography (EBL) is a versatile technique for creating arbitrary patterns on substrates with sub-10 nm resolution. Contrary to conventional lithography techniques, EBL was previously shown to be able to pattern non-planar surfaces using modified lithography system to adjust the beam position along z-axis, spray coating of the resist, and evaporation of the resist. Among them, evaporation of the resist is more favorable as it can be done on any irregular surfacesurfaces using commonly available thermal evaporation equipment. Yet, previous evaporated resist materials suffer from low resolution and sensitivity, as well as poor dry etching resists for subsequent pattern transfer to the sub-layer. Here, evaporation of polystyrene electron beam resist is studied which was used to pattern on irregular surfaces such as the cantilever of atomic force microscope and side surface of an optical fiber. Furthermore, in order to drastically increase the resist’s dry etching resistance, chromium that is a hard etching mask material was successfully incorporated into the resist by co-evaporating or Cr and polystyrene. This nanocomposite resist enabled the fabrication of very high aspect ratio structures by electron beam lithography followed by dry plasma etching. As this material can be evaporated on any substrate, including non-planar surfaces, it can open new era to spectroscopy and bio-sensing techniques. Part II (Chapter 5-6) presents a low-cost bottom-up fabrication techniques for creatingto create dense surface nanostructures without long-range ordering. Recently, micro- and nano-structured surfaces have become a hot topic in nanotechnology where performance of devices is enhanced due to such surface nanostructuring. Such structures are often called as a “smart” coating on the surfaces where they could provide wetting/de-wetting, adhesion, thermal and/or electrical conductivity, super-hydrophobicity, self-cleaning, anti-icing, anti-reflectivity, etc. Bottom-up techniques, such as self-assembly lithography, areis undoubtedly much more cost-effective than top down lithography techniques for applications that do not need long range ordering. Block co-polymer lithography, colloidal lithography, sol-gel processing, wet/dry etching are some commonly used techniques of bottom-up fabrication. However, fabrication of those structures with low costslow-cost as well as high performance is still challenging. Here a novel fabrication method is introduced, which involves spin-coating of metal salt : polymer composite followed by its phase-separation upon thermal annealing. Both spin-coating and thermal annealing are very low- cost processes. With this method, after pattern transfer to the substrate using the self-formed metal salt islands as mask, dense and high resolutionhigh-resolution nanostructures over large area without long-range ordering is achieved, which offered greatly enhanced super-hydrophobic and anti-reflective properties

Nanofabrication and its Application in Atomic Force Microscopy (AFM)

This thesis is focused on nanofabrication and its application in atomic force microscopy (AFM). The contribution of this thesis is thus the development, investigation and characterization of novel nanofabrication technique (Part I); and application of nanofabrication in manufacturing the high aspect ratio AFM tips (Part II). In the first part of the thesis, firstly, unlike optical and mechanical lithography such as nanoimprint lithography, the throughput of EBL is very low, which demands for highly sensitive resists. We studied the dependency of e-beam exposure properties on molecular weight of the negative EBL resist polystyrene, and very high sensitivity of 1 µC/cm2 was obtained for 900 kg/mol when exposed with electron beam of 2 keV. We also demonstrated that the exposure property of high PDI (polydispersity index) polystyrene resembles that of a monodisperse (PDI 1.06) polystyrene with similar number averaged molecular weight ("Mn" ) ̅, which indicates that it is ("Mn" ) ̅ rather than ("Mw" ) ̅ (weight averaged molecular weight) that dominates the exposure properties of polystyrene resist. Secondly, lift-off using negative resist is very challenging because the resist profile is typically positively tapered due to electron forward scattering, and upon exposure negative resist is cross-linked and thus insoluble in solvents. Here we demonstrated that low energy exposure could circumvent both issues simultaneously, and we achieved liftoff of Cr with polystyrene resist using a solvent xylene. Lastly, since low energy electrons are mostly stopped inside the resist layer, radiation damage to the sub-layer is greatly reduced. Thirdly, an electron beam resist is usually coated by conventional coating methods such as spin-coating, but this cannot be reliably applied on irregular surfaces. We here reported a monolayer resist can be grafted on nonflat surface. As a proof of concept of patterning on irregular surfaces, we chose PMMA mono-layer "brush" and grafted it on irregular surfaces by thermal treatment which accelerates a chemical reaction between PMMA molecules and hydroxyl group on substrate. We achieved nanofabrication of 30 nm resolution on an AFM cantilever. Fourthly, due to the lack of feedback, conventional electron beam lithography (EBL) is a “blind” open-loop process where the exposed pattern is examined only after ex-situ resist development, which is too late for any improvement. We reported that self-developing resist nitrocellulose, for which pattern shows up right after exposure without ex-situ development, can be used as in-situ feedback on the e-beam distortion and enlargement. Once the beam was optimized using nitrocellulose resist, under the same optimal beam condition, we exposed in the common resist PMMA. We achieved ~80 nm resolution across the entire large writing field of 1 mm2, as compared to 210 nm without the beam optimization process. We also reported that self-developing resist can provide in-situ feedback for writing field alignment accuracy, which in turn can be used to optimize the alignment. In the second part of the thesis, we demonstrated the batch fabrication of high aspect ratio (HAR) AFM tips. In order to obtain high quality and faithful images in AFM, very high aspect ratio tips are required in order to reach to the bottom of narrow and deep trenches/holes. But these HAR tips are extremely difficult to make and consequently very expensive. Currently all the commercially available HAR AFM tips are fabricated in a slow, costly (~5-20 that of regular AFM tips) and serial manner (one by one). We here developed a method to batch fabricate HAR AFM tips by forming a hard metal etching mask just on the apex of the pyramid tip followed by silicon dry etching to achieve the HAR pillar right below the metal island mask. Since it is a batch and lithography-free process, it has much higher throughput and much lower manufacturing cost per tip. This technique was first successfully applied on large-area pyramid arrays and then transferred to the commercial regular AFM tips, and has demonstrated the uniformity, reproducibility and yield of those HAR tips. The tip apex diameter and tip pillar height are controllable by tuning metal thickness and silicon dry etching time respectively. Finally, we demonstrated that the HAR tips fabricated using our technique gave a better imaging quality than the commercial regular tips.1 yea

Nanophotonic antennas for enhanced single-molecule fluorescence detection and nanospectroscopy in living cells membranes

Cotutela Universitat Politècnica de Catalunya i Aix-Marseille UniversitéSingle-molecule fluorescence spectroscopy has revolutionized the field of biophysical sciences by enabling visualization of dynamic molecular interactions and nanoscopic features with high spatiotemporal resolution. Monitoring enzymatic reactions and studying diffusion dynamics of individual molecules (such as lipids and proteins) help us understand how these nanoscopic entities influence and control various biochemical processes. Nanophotonic antennas can efficiently localize electromagnetic radiation into nanoscale spatial dimensions comparable to single bio-molecules (<10 nm). These ultra-confined illumination hotspots thereby offer opportunity to follow single-molecule events at physiological expression levels. In this thesis, we explore various photonic nanoantenna platforms (double nanohole apertures, dimer nanogap antennas and planar "antenna-in-box'') and demonstrate their application in enhanced single-molecule fluorescence detection. Using fluorescence burst analysis, fluorescence correlation spectroscopy (FCS), time-correlated TCSPC measurements, and near field simulations, we quantify nanoantenna detection volumes, fluorescence enhancement factors and discuss the fluorescence photodynamic accelerations mediated by optical nanoantennas. An alternative to plasmonic structures, all-dielectric nanoantenna based on silicon nanogap is also demonstrated to enhance the fluorescence detection of single molecules diffusing in concentrated solutions. Further, using resonant planar "antenna-in-box'' devices we investigate the diffusion dynamics of phosphoethanolamine and sphingomyelin on the plasma membrane of living cells and discuss the results in the context of lipid rafts. Together with cholesterol depletion experiments, we provide evidence of cholesterol-induced nanodomain partitioning within less than 10 nm diameters and characteristic times being ~100 microsecondsLa espectroscopia de fluorescencia de una sola molecula ha revolucionado el campo de las ciencias biofisicas, permitiendo la visualizacion de interacciones moleculares dinamicas y caracteristicas nanoscopicas con alta resolucion espaciotemporal. La monitorizacion de las reacciones enzimaticas y el analisis de la dinamica de difusion de moleculas individuales (como lipidos y proteinas) nos ayudan a comprender como estas entidades nanoscopicas influyen y controlan diversos procesos bioquimicos. Las antenas nanofotonicas pueden localizar eficientemente la radiacion electromagnetica en dimensiones espaciales en nanoescala, comparables a biomoleculas unicas (<10 nm). Estos hotspots de iluminacion ultra configurados ofrecen de este modo la oportunidad de monitorizar eventos de molecula unica a niveles de expresion fisiologica. En esta tesis, exploramos varias plataformas fotonicas de nanoantenas (double nanohole aperture, dimero nanogap antenas y "antenna-in-box" planares) y demostramos su aplicacion en la mejora de la deteccion una sola molecula de fluorescencia. Utilizando el analisis por explosion de fluorescencia, espectroscopia de correlacion de fluorescencia (FCS), medidas TCSPC correlacionadas en el tiempo y simulaciones de campo cercano, cuantificamos volumenes de deteccion de nanoantenas, factores de mejora de fluorescencia y discutimos las aceleraciones fotodinámicas de fluorescencia mediada por nanoantennas opticas. Las nanoantennas dielectricas basadas en nanogaps de silico se han propuesto como una alternativa en el realce de la deteccion de fluorescencia de difusion de moleculas unicas en soluciones concentradas. Ademas, utilizando dispositivos resonantes planares de "antenna-in-box", investigamos la dinamica de difusion de la fosfoetanolamina y la esfingomielina en la membrana plasmatica de las celulas vivas y discutimos los resultados en el contexto de las balsas lipidicas. Junto con experimentos de dismincion de colesterol, proporcionamos pruebas de division inducida por colesterol en el nanodominio dentro de diametros menors de 10 nm y con tiempos caracteristicos de ~100 microsegundos.La spectroscopie de fluorescence d'une seule molécule a révolutionné le domaine des sciences biophysiques, permettant la visualisation d'interactions moléculaires dynamiques et de caractéristiques nanoscopiques à haute résolution spatio-temporelle. Le suivi des réactions enzymatiques et l'analyse de la dynamique de diffusion des molécules individuelles (telles que les lipides et les protéines) nous aident à comprendre comment ces entités nanoscopiques influencent et contrôlent divers processus biochimiques. Les antennes nanophotoniques peuvent localiser efficacement le rayonnement électromagnétique à des dimensions spatiales nanométriques, comparables à des biomolécules uniques (<10 nm). Ces hotspots d'éclairage ultra-configurés offrent la possibilité de surveiller les événements de molécules uniques à des niveaux d'expression physiologiques. Dans ce mémoire, nous examinons plusieurs plates-formes photoniques nanoantennas (nanotrou à double ouverture, I antennes Dimer nanoespace et plane « antenne-in-box ») et de démontrer son application dans l'amélioration de la détection d'une fluorescence seule molécule. Utilisation de l'analyse par spectroscopie de fluorescence d'explosion corrélation de fluorescence (FCS), les mesures TCSPC corrélées dans le temps et proches des simulations champ quantifier les volumes de détection de nanoantennas, les facteurs d'amélioration fluorescence et discuter des accélérations photodynamiques fluorescence médiée nanoantennas opticas. Des nanoantennas diélectriques à base de nanogap silico ont été proposées comme alternative dans l'amélioration de la détection par fluorescence de la diffusion de molécules uniques dans des solutions concentrées. En outre, l'utilisation de "plan d'antenne-in-box" dispositifs de résonance, nous étudions la dynamique de diffusion de phosphoéthanolamine et sphingomyéline dans la membrane plasmique des cellules vivantes et de discuter des résultats dans le contexte des radeaux lipidiques. Conjointement avec des expériences de réduction du cholestérol, nous fournissons des tests de division induits par le cholestérol dans le nanodomaine dans des diamètres plus petits de 10 nm et avec des temps caractéristiques de ~ 100 microsecondes.Postprint (published version