Optofluidic sensing utilizes the advantages of both microfluidic and optical science to achieve tunable and reconfigurable high-performance sensing purpose, which has established itself as a new and dynamic research field for exciting developments at the interface of photonics, microfluidics, and the life sciences. With the trend of developing miniaturized electronic devices and integrating multi-functional units on lab-on-a-chip instruments, more and more desires request for novel and powerful approaches to integrating optical elements and fluids on the same chip-scale system in recent years. By taking advantage of the electrowetting phenomenon, the wettability of liquid droplet on micro/nano-structured surfaces and the Leidenfrost effect, this doctoral research focuses on developing high-performance optofluidic sensing systems, including optical beam adaptive steering, whispering gallery mode (WGM) optical sensing, and surface-enhanced Raman spectroscopy (SERS) sensing. A watermill-like beam steering system is developed that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5°/s. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor network. Furthermore, the WGM sensing system is demonstrated to be stimulated along the meridian plane of a liquid microdroplet, instead of equatorial plane, resting on a properly designed nanostructured chip surface. The unavoidable deformation along the meridian rim of the sessile microdroplet can be controlled and regulated by tailoring the nanopillar structures and their associated hydrophobicity. The nanostructured superhydrophobic chip surface and its impact on the microdroplet morphology are modeled by Surface Evolver (SE), which is subsequently validated by the Cassie-Wenzel theory of wetting. The influence of the microdroplet morphology on the optical characteristics of WGMs is further numerically studied using the Finite-Difference Time-Domain method (FDTD) and it is found that meridian WGMs with intrinsic quality factor Q exceeding 104 can exist. Importantly, such meridian WGMs can be efficiently excited by a waveguiding structure embedded in the planar chip, which could significantly reduce the overall system complexity by eliminating conventional mechanical coupling parts. Our simulation results also demonstrate that this optofluidic resonator can achieve a sensitivity as high as 530 nm/RIU. This on-chip coupling scheme could pave the way for developing lab-on-a-chip resonators for high-resolution sensing of trace analytes in various applications ranging from chemical detections, biological reaction processes to environmental protection. Lastly, this research reports a new type of high-performance SERS substrate with nanolaminated plasmonic nanostructures patterned on a hierarchical micro/nanostructured surface, which demonstrates SERS enhancement factor as high as 1.8 x 107. Different from the current SERS substrates which heavily relies on durability-poor surface structure modifications and various chemical coatings on the platform surfaces which can deteriorate the SERS enhancement factor (EF) as the coating materials may block hot spots, the Leidenfrost effect-inspired evaporation approach is proposed to minimize the analyte deposition area and maximize the analyte concentration on the SERS sensing substrate. By intentionally regulating the temperature of the SERS substrate during evaporation process, the Rhodamine 6G (R6G) molecules inside a droplet with an initial concentration of 10-9 M is deposited within an area of 450 μm2, and can be successfully detected with a practical detection time of 0.1 s and a low excitation power of 1.3 mW. / Doctor of Philosophy / Over the past two decades, optofluidics has emerged and established itself as a new and exciting research field for novel sensing technique development at the intersection of photonics, microfluidics and the life sciences. The strong desire for developing miniaturized lab-on-a-chip devices and instruments has led to novel and powerful approaches to integrating optical elements and fluids on the same chip-scale systems. By taking advantage of the electrowetting phenomenon, the wettability of liquid droplet on micro/nano-structured surfaces and the Leidenfrost effect, this doctoral program focuses on developing high-performance optofluidic sensing systems, including optical beam adaptive steering, whispering gallery mode (WGM) optical sensing, and surface-enhanced Raman spectroscopy (SERS) sensing. During this doctoral program, a rotary electrowetting-on-dielectric (EWOD) beam steering system was first fabricated and developed with a wide lateral steering range of 360° and a fast steering speed of 353.5°/s, which can be applied in telecommunication systems or lidar systems. Next, the meridian WGM optical sensing system was optically simulated using finite difference time domain (FDTD) method and was numerically validated to achieve a high quality-factor Q exceeding 104 and a high refractive index sensitivity of 530 nm/RIU, which can be applied to the broad areas of liquid identification or single molecule detection. Lastly, a SERS sensing platform based on a hierarchical micro/nano-structured surface was accomplished to exhibit a decent SERS enhancement factor (EF) of 1.81 x 107. The contact angle of water droplet on the SERS substrate is 134° with contact angle hysteresis of ~32°. Therefore, by carefully controlling the SERS surface temperature, we employed Leidenfrost evaporation to concentrate the analytes within an extremely small region, enabling the high-resolution detection of analytes with an ultra-low concentration of ~10-9 M.

Among various energy harvesting technologies reverse electrowetting-on-dielectric energy harvesting (REWOD) has been proved to harvest energy from low frequency motion such as many human motion activities (e.g. walking, running, jogging etc.). Voltage rectification and DC-DC boosting of low magnitude AC voltage from REWOD can be used to reliably self-power the wearable sensors. In this work, a commercial component-based rectifier and DC-DC converter is designed and experimentally verified, for further miniaturization standard 180 nm CMOS process is used to design the rectifier and the DC-DC boost converter.This work also includes the MATLAB based model for REWOD energy harvester for various REWOD models. In REWOD energy harvesting, a mechanical input during the motion causes the electrolyte placed in between two dissimilar electrodes to squeeze back and forth thereby periodically changing the effective interfacial area, hence generating alternating current. The alternating current is given to the rectifier design. There is no realistic model that has been developed yet for this technique. Thereby, a MATLAB based REWOD model is developed for the realistic simulation of the REWOD phenomenon. In the work, a comparison of different REWOD models such as planar surface, rough surface and porous models are performed demonstrating the variations in capacitance, current and voltage.

La recherche développée durant cette thèse constitue la première étape de développement d’une nouvelle méthodologie de détection sans marquage à l’échelle d’une goutte : un nouveau mécanisme de transduction est développé, basé sur l’actuation par électromouillage bi-fréquence d’un réseau d’ondes capillaires à la surface d’une goutte. La résonance capillaire de la goutte est étudiée par détection interférométrique de son apex en mouvement.La faisabilité de cette méthodologie est prouvée en caractérisant la cinétique d’évaporation de la goutte par glissement spectral des ondes capillaires.La deuxième partie de la thèse porte sur la modélisation du transport de biomolécules tensioactives dans une goutte : le transport diffusif, les processus d’ad/désorption aux surfaces, la condition cinématique d’un rayon variable(évaporation) ainsi qu’une quantité molaire finie de biomolécules sont pris en compte. Un nouveau nombre adimensionnel est proposé pour rendre compte de la taille finie d’une goutte. Puis le transport chimique associé au courant de dérive induit par les ondes capillaires (excitées par électromouillage oscillatoire)est pris en compte à l’aide de simulations numériques. Finalement,l’électromouillage haute et basse fréquence est appliqué au cas d’une goutte enrichie par des molécules d’albumine de sérum bovin. En utilisant conjointement l’interférométrie optique et l’imagerie, et en considérant la loi de Lippmann-Young, le vieillissement biochimique de la surface solide mouillée par la goutte est détecté. / This PhD research is thought of as a first step towards label freedigital biosensing. A novel transduction mechanism is developed, based on thegeneration of capillary waves along a drop surface induced by dual-frequencyelectrowetting. Acapillary resonance is measured by interferometry at the movingdrop apex. Aproof of concept of this electro-optical methodology for furtherintegration in a digital microsystem is given with characterization of drop evaporationkinetics. A second part focuses on modeling and numerical calculationsof the transport of surface active biomolecules in the drop. The model includesdiffusion, ad-/desorption phenomena together with a kinematic condition of avariable drop radius (evaporation) as well as a finite molecular amount of surfaceactive biomolecules. A dimensionless number is suggested to take into accountfinite size effects. Drop steady streaming due to oscillating electrowetting isfinally taken into account. Low- and high-frequency electrowetting is appliedto a drop laden with bovine serum albumin. By jointly using interferometry andimaging, enhancement of surface ageing is made evident under electrowetting.

The characterization and fabrication of active matrix thin film transistors (TFTs) has been studied for an addressable microfluidic electrowetting channel device as application. A new transparent semiconductor material, Amorphous Indium Gallium Zinc Oxide (a-IGZO), is used for TFT, which shows high electrical performance rather than amorphous silicon based TFT; higher mobility and even higher transparency. The purpose of this dissertation is to optimize each TFT process including the optimization of a-IGZO properties to achieve robust device for application. To minimize hysteresis of TFT curves, the gate dielectric is discussed extensively in this dissertation. By optimizing gas ratio of NH3SiH4, it is found that the TFT with NH3 rich SiNx gate dielectric deposited with NH3/SiH4 =5.1 and stoichiometric SiO2 demonstrates best condition to reduce hysteresis. a-IGZO films is investigated as a function of power and substrate bias effect which affects to electrical performance; the higher power and substrate bias increase the carrier density in the film and mainly cause threshold voltage(VT) to shift in the negative gate voltage direction and mobility to increase, respectively. In addition, the powerful method to estimate the electrical properties of a-IGZO is proposed by calculating O2 and IGZO flux during sputtering in which the incorporation ratio with O2/IGZO ≈1 demonstrates the optimized a-IGZO film for TFT. It is confirmed that both physical and chemical adsorption affects the electrical property of a-IGZO channel by studying TFT-IV characteristics with different pressure and analyzing X-ray photoelectron spectroscopy (XPS), which mainly affects the VT instability. The sputtered SiO2 passivation shows better electrical performance. To achieve electrically compatible (lower back channel current) a-IGZO film to SiO2 sputter passivated device, a-IGZO TFTs require oxygen rich a-IGZO back channel by employing two step a-IGZO deposition process (2nd 10nm a-IGZO with PO2 = 1.5mTorr on 1st 40nm a-IGZO with PO2=1mTor). Electrowetting microfluidic channel device as application using a-IGZO TFTs is studied by doing preliminary test. The electrowetting channel test using polymer post device platform is candidate for addressable electrowetting microfluidic channel device driven by active matrix type a-IGZO TFT.

No description available.

Les surfaces de polymères électro-stimulables font partie de la catégorie des surfacesintelligentes. Elles sont capables de modifier leurs propriétés lorsqu’elles sont stimulées par unchamp électrique. Au cours de cette thèse nous avons fabriqué des surfaces de chaines depolyélectrolytes faibles greffées (PAA, P2VP, PDMAEMA), soit par auto-assemblage, soit partransfert via la balance de Langmuir. Nous avons ensuite étudié l’organisation des chaines depolyélectrolytes à la surface en fonction des conditions de pH et de sel de la sous-phase dans labalance de Langmuir. Avant de stimuler ces chaines de polyélectrolytes greffées à l’aide d’unchamp électrique, nous avons étudié leur sensibilité à la variation de pH et à la variation de laconcentration en sel. Pour cela des mesures d’épaisseurs de films de polyélectrolytes et desmesures d’angle de contact ont été effectuées. Ces études préliminaires nous ont permis desélectionner des valeurs de densité de greffage des chaines de polyélectrolytes ainsi que le pH etla concentration en sel de la solution adaptés pour la stimulation des surfaces par un champélectrique. Nous avons alors montré que les chaines greffées de PAA et de PDMAEMA étaienttrès sensibles à la variation de la tension électrique lorsque le pH est proche du pKa ou du pKb dela surface : pour une charge de la surface identique aux charges des chaines de polyélectrolytes,ces dernières vont adopter une conformation de brosse tandis qu’elles seront collapsées lorsque lacharge de la surface est de signe opposé aux charges des chaines. Cette transition réversible deschaines en fonction de la valeur de la tension appliquée permet de contrôler les propriétés demouillage et d’adhésion de ces surfaces. En revanche, pour un pH proche du pKb, les chainesgreffées de P2VP sont peu sensibles à l’application d’un champ électrique. Nous avons supposéque cela était dû à une variation de pH local au sein des chaines lorsque le champ électrique estappliqué. / Electro-responsive polymer surfaces are able to change their properties when they are stimulatedby an electric field. In this work, we grafted weak polyelectrolyte on surfaces by self-assembly orby transferring the molecules using the Langmuir-Schaefer method. First we studied theorganization of the polyelectrolyte chains at the surface for different pH and salt concentration ofthe subphase used in the Langmuir trough. Then we explored the response of the surfaces to pHand salt concentration changes by measuring the thickness variation of the polyelectrolyte filmsand the changes in contact angle. These preliminary studies allowed us to select the graftingdensity of polyelectrolyte chains and the pH and salt concentrations of the aqueous solutionadapted for the stimulation of the surfaces by an electric field. We then demonstrated that PAAand PDMAEMA grafted chains were very sensitive to the variation of the applied voltage whenthe pH is close to the pKa or from the pKb of the surface. If the charge of the surface has the samesign as the charges on the polyelectrolyte chains, the latter would adopt a brush conformation,whereas if the charge of the surface has the opposite sign compared to the sign of the charges onthe polyelectrolyte chains, the chains would collapse. This reversible transition of the chainsconformation with the sign of the applied voltage allowed us to control the wetting and theadhesion properties of these surfaces. Nevertheless, for a pH close to the pKb, the P2VP graftedchains are almost unresponsive to the application of an electric field. We supposed that this is theconsequence of a local pH variation inside the grafted chains when the electric field is applied.

No description available.

Dans le but d'améliorer la fiabilité des technologies utilisant l'électromouillage, l'objectif de cette thèse est d'étudier les mécanismes de vieillissement de matériaux diélectriques et hydrophobes utilisés en électromouillage et d'appliquer ensuite le protocole de caractérisation établi, à de nouveaux matériaux. Cette thèse s'articule en trois parties. Dans une première partie, afin de caractériser finement les propriétés d'hydrophobie de surfaces et de déterminer plus particulièrement leur polarité, nous avons mis au point une méthode de mesure de la polarité de surface basée sur le mouillage de deux liquides sur une surface, ce qui apporte une précision accrue avec un minimum de mesures. Dans une deuxième partie, nous avons étudié différents revêtements utilisés en électromouillage avant et après vieillissement. Nous nous sommes plus particulièrement intéressés aux films hydrophobes largement utilisés dans les systèmes optiques et de micro-laboratoires comme le Fluoropel©, le Cytop© et le parylène C. Cette étude montre une altération non négligeable des performances des matériaux de manière reproductible. L'hystérésis de mouillage, l'angle de contact au repos ainsi que les propriétés de cohésion des couches ont été étudiés afin de mettre en évidence les paramètres critiques à la durée de vie.Dans la dernière partie, nous avons cherché à mettre au point une méthode de dépôt d'un nouveau matériau hydrophobe par deux techniques de synthèse ; la voie sol-gel et la pulvérisation cathodique (PVD). Ainsi, un sol de précurseur à base du métal applicable pour la préparation de couches minces de son oxyde a été élaboré. La solution est obtenue à partir d'un précurseur synthétisé au laboratoire et stabilisée par des chélatants (acétylacétone). La stabilité de la solution ainsi que la procédure de dépôt sont présentées et les revêtements recuits déposés par sol-gel et PVD sont caractérisés par DRX et d'un point de vue morphologique (MEB, microscope optique…). Si, il fut possible de préparer par la méthode sol-gel des films de 300nm couvrants, leur forte rugosité n'a pas permis de les tester en électromouillage. Par la méthode PVD, nous avons pu réaliser des couches de 400 nm d'épaisseur, très lisses et utilisables en électromouillage. Ces films donnent de très bons résultats en électromouillage sur substrats plans et en lentilles liquides / In order to increase the technologies reliability using electrowetting, this work aims to study the mechanisms of ageing on dielectric and hydrophobic materials used in electrowetting as well and to apply this study to new materials. This thesis is composed of three parts.First, to be able to characterize precisely the hydrophobic properties of these surfaces and especially their surface polarity, we established a method to measure the surface polarity based on wettability of two liquids on a surface permitting a better precision with less measurements. In a second part, we studied different films used in electrowetting before and after ageing around 90°C for one week in order to simulate a long term ageing at an ambient temperature. Widely used hydrophobic coating used in optical systems and lab-on-chip will be mainly characterized such as Fluoropel©, Cytop© and parylène C. This work shows the visible alteration of material performances in a reproducible way. Wetting hysteresis and natural contact angle with the cohesive properties of the coatings are studied in order to establish critical parameters for the life time.Finally, we tried to establish a method to deposit a hydrophobic metal oxide coating by two ways, sol-gel technic with dip-coating deposition and by PVD. A precursor sol made of the metal usable to deposit its oxide thin films has been elaborated. The solution is prepared from the synthesized precursor and stabilized by chelatant (acetylacetone). The solution stability as well as the deposition method used are presented and the annealed coatings deposited by sol-gel and PVD are characterized by XRD and morphologically (SEM, optic microscope …). By the sol-gel method, covering coatings of about 300nm have been made. However, because of the roughness, no electrowetting experiments could have been achieved. By PVD, we have deposited coatings of 400nm thickness, very smooth and usable in electrowetting. These coatings give very good results in electrowetting on plane substrates and liquid lenses

In this dissertation physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wetting line) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL) phenomena which encompass the wetting line energy (WLE) or pinning, the wetting line velocity (WLV), and the contact angle hysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the interfacial phenomena such as the air film lubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium states of water droplets on liquid free surfaces. EWOD was implemented to devise a pumping method for a continuous flow in a microchannel. An active micropump with a simple layout and no moving parts is designed and fabricated which has on demand flow on/off capability. The micropump is based on droplet/meniscus pressure gradient generated by EWOD. By altering the contact angle between liquid and solid using an electric field a pressure gradient was induced and a small droplet was pumped into the channel via a uniform flow rate. A surface tension based propellant method was introduced as a low power consumption actuation method in microfluidic devices. For an initial droplet volume of 0.3µL and a power of 12nW a constant flow rate of 0.02µL/sec was demonstrated. Sample loading on-demand could be achieved by regulating an electric potential. Unexpectedly, the flow rate of the pump was found to be constant in spite of the changes in the droplet’s radius, which directly affects the pump’s driving pressure. iv The WL phenomena were studied in details to unravel the physical concept behind the micropump constant flow rate during the operation. An interesting observation was that the shrinking input droplet changes its shape in two modes in time sequence: (i) in the first mode its contact angle decreases while its wetting area remains constant due to the pinning, (ii) in the second mode the droplet’s WL starts to move while its contact angle changes as a function of its velocity. Contact angles were measured for the droplet advancing and receding WLs at different velocities to capture a full picture of contact angle behavior due to pinning and WLV effects. These results are also relevant to the meniscus inside the channel. The changes on the contact angle caused by the presence of EWOD at the bottom of the channel were studied in detail. The EWOD based micropump was used as a platform to study the contribution of the pinning and WLV effects on its constant flow rate. The effects of the WLE on the static contact angle and the WLV on the dynamic contact angle in the pump operation were investigated. Also the effect of EWOD voltage on the magnitude and uniformity of the micropump flow rate was studied. Dynamic contact angles (as a function of pinning and WLV) were used to accurately calculate the pressure gradient between the droplet and the meniscus and estimate the flow rate. It was shown that neglecting either of these effects not only results in a considerable gap between the predicted and the measured flow rates but also in an unphysical instability in the flow rate analysis. However, when the WLE and WLV effects were fully taken into account, an excellent agreement between the predicted and the measured flow rates was obtained. v For the study of the TCL between three fluids, aqueous droplets were formed at oil-air interface and two stable configurations of (i) non-coalescent droplet and (ii) cap/bead droplet were observed. General solutions for energy and force analysis were obtained and were shown to be in good agreement with the experimental observations. Further the energy barrier obtained for transition from configuration (i) to (ii), was correlated to the droplet release height and the probability of non-coalescent droplet formation. Droplets formed on the solid surfaces and on the free surface of immiscible liquids have various applications in droplet-based microfluidic devices. This research provides an insight into their formation and manipulation.

Il y a à l'heure actuelle un grand besoin d'antennes reconfigurables dans la bande des 60 GHz pour des applications de télédétection et de télécommunications sans fil très hauts débits. Les solutions traditionnelles de reconfiguration sont basées sur des semiconducteurs ou des composants RF-MEMS, qui connaissent un coût, une complexité et des pertes croissantes en bande millimétrique. Dans cette thèse, une approche originale a été développée : elle est basée sur la reconfiguration mécanique d'antennes et dispositifs millimétriques microrubans sur substrat élastomère ultrasouple PDMS grâce à des actionneurs MEMS grands déplacements. Premièrement, les choix de conception, la technique de simulation éléments finis (HFSS), et surtout la microfabrication d'antennes sur membrane PDMS ainsi que les techniques de mesure en impédance et rayonnement sont abordés.Deux axes ont ensuite été étudiés : les antennes accordables en fréquence, et les antennes et composants pour le balayage angulaire (déphaseurs et antennes à balayage mécanique de type scanner). Des procédés technologiques innovants ont été développés (reports de métallisations épaisses biocompatibles et d'aimants permanents en couches minces sur membrane PDMS) et différentes techniques d'actionnement (pneumatique, magnétique, par électromouillage) ont été mises en œuvre. Les performances en terme d'accord en fréquence (8,2 %) et de balayage angulaire (-90/+100°) dépassent l'état de l'art des antennes du même type en bande millimétrique, et ceci en utilisant une technologie peu complexe, ultra bas-coût et prometteuse pour la montée en fréquence. / There is currently an increasing need for reconfigurable antennas in the 60 GHz band for remote sensing applications and wireless communications. Traditional reconfiguration solutions are based on semiconductors or RF-MEMS but these components face cost, complexity and losses issues at millimeter-waves.In this thesis, an original approach was developed: it is based on the mechanical reconfiguration of millimeter-wave microstrip antennas and devices printed on ultrasoft PDMS substrates, thank to large displacements MEMS actuators. First, the design choices, the finite element simulation technique (HFSS), and the microfabrication of antennas supported by PDMS membranes as well as the impedance and radiation measurements techniques have been discussed. Two axis have then been studied: frequency-tunable antennas, and beam-steering components (phase shifters and "scanner" type antennas). Innovative technological processes were developed (transfer of biocompatible metal patterns and permanent magnet thin films on PDMS membranes) and several actuation techniques (pneumatic, magnetic, electrowetting) were implemented. Performances in terms of frequency tuning (8.2%) and scan angles (-90 / 100 °) are beyond the state of the art for similar antennas in the millimeter-wave band, and are achieved by using a very simple, ultra low-cost technique that is expected to be effective at even higher frequencies.