Dans le cadre de la thèse, l'étude porte sur le développement de microbatteries lithium tout solide, dans l'objectif d'alimenter les microsystèmes radiofréquences. On s'est intéressé particulièrement à la miniaturisation et à certains aspects de l'intégration de ces microbatteries. Une première étape a consisté à établir une étude physiochimique des couches actives, et particulièrement l'électrode positive en pentoxyde de vanadium (V2O5), et d'évaluer le comportement électrochimique de ce composé au sein de la microbatterie. Le suivi du matériau par différentes méthodes de caractérisation pendant la phase de croissance a permis l'observation de variations significatives de ses propriétés structurales et morphologiques. Une corrélation a été établie entre ces caractéristiques physiochimiques et le comportement électrochimique à la fois en électrolyte liquide et solide (V2O5/LiPON/Li). Un procédé de microfabrication a été ensuite proposé pour la miniaturisation des microbatteries. Le procédé comporte plusieurs briques technologiques faisant appel à la photolithographie et différentes techniques de gravure. Un protocole expérimental a été établi afin d'optimiser, qualifier et valider le développement de chaque brique technologique, et de rendre compte de la fonctionnalité des dépôts actifs après microfabrication. La conception de microbatteries a été finalement réalisée en se basant sur le cahier des charges du microsystème radiofréquence considéré et en tenant compte du procédé de microfabrication développé. / Within the context of this thesis, achieved works focuses on developing all solid state thin film microbatteries, with the aim of powering radio frequency microsystems (RF MEMS). It was particulary interested on the miniaturization and specific aspects of the integration of these microdevices. A first step xas related to physicochemical investigations on active layers. It has been particulary focused on the positive electrode of vanadium pentoxide (V2O5), so as to assess the electrochemical behaviour of this compound within the microbattery architecture. The monitoring of the material through several characterization techniques during the growth phases has allowed the observation of changes in its structural and morphological properties. A correlation was established between these physicochemical characteristics and the electrochemical behavior in both liquid and solid electrolyte configurations. A microfabrication process was then proposed for the miniaturization of microbatteries. The process involves several process blocks using photolithography and etching techniques. An experimental protocol has been established to optimize, qualify and validate the development of each process block, and investigate the functionality of deposited active layers after microfabrication steps. The design of microbatteries was finally achieved on the basis of the specifications of the selected RF MEMS and taking into account the developed global microfabrication process flow.

Neste trabalho são apresentados resultados relativos ao desenvolvimento de um processo de fabricação para a produção de sistemas de microcanais em vidro tipo borosilicato, 7059 Corning Glass. O objetivo do trabalho é implementar um processo básico, mas completo, de fabricação de sistemas microfluídicos em vidro, que possam futuramente ser aprimorados com a introdução de dispositivos ópticos e eletrônicos e de elementos microfluídicos ativos, como válvulas e microbombas, para sensoreamento e controle de fluxo. O processo de fabricação foi dividido em três grandes etapas, sendo a primeira delas, a produção dos microcanais, envolvendo processos como litografia e corrosão úmida. Nos estudos de corrosão procurou-se uma solução que permitisse a obtenção de canais com superfície uniforme e lisa, sem a produção de resíduos durante a corrosão do vidro. Os melhores resultados foram obtidos com a solução HF + HCl + H2O (1:2:3), com a possibilidade de produzir canais com até 150 µm de profundidade. A segunda etapa do processo de produção dos sistemas microfluídicos envolveu o encapsulamento dos microcanais, o que foi feito através de um processo de soldagem direta (vidro com vidro) à temperatura ambiente, com aplicação de pressão entre 0,1 a 1,0 MPa. Os melhores resultados nesta etapa envolveram pressões acima de 0,5 MPa, podendo-se obter cerca de 95 - 100% da área das lâminas soldadas. A terceira etapa do processo de fabricação engloba a interconexão com o meio externo, envolvendo a produção dos furos no vidro para entrada e saída de líquidos e a introdução dos tubos de acesso para o meio externo. Para a produção dos furos foi desenvolvido um sistema posicionador computarizado que movimenta o substrato de vidro nas direções x, y e z com precisão de alguns micrometros, garantindo o alinhamento necessário entre as duas lâminas de vidro que devem ser soldadas para encapsular os microcanais. Os furos foram feitos com broca diamantada de uso odontológico fixa em uma furadeira comum. Cateteres e scalps de uso médico foram empregados como tubos de acesso, sendo selados com resina epóxi. Os sistemas microfluídicos fabricados foram testados monitorando o fluxo de soluções aquosas de anilina, o qual foi mantido através de bomba peristáltica. Os resultados se mostraram reprodutíveis, tendo se obtido microcanais lisos e sem resíduos, sem apresentar vazamentos e exibindo regime de fluxo tipicamente laminar. Em conjunto, estes resultados mostraram-se muito promissores para desenvolvimento futuro de aplicações em áreas como Biotecnologia e Análises Químicas. / In this work, a process for the fabrication of microchannels over borlosilicate 7059 Corning Glass is presented. The main objective is to develop a simple and complete process for the fabrication of microfluidic systems over glass, that can be further improved in the future, with the integration of optical, electronic and active microfluidic devices such as valves and micropumps, for sensing and flow control. The fabrication process has three main parts. The first part is the microchannel production, which is achieved through contact-lithography and wet etching. In the etching studies, a solution that led to the fabrication of channels with uniform and smooth surfaces, without residue formation was sought. The best results were attained with a HF + HCl + H2O (1:2:3), which allow for the production of channels with depths of up to 150 µm. The second part of the fabrication process is the microchannels encapsulation, which is achieved through direct (glass-glass) bonding at room temperature, with applied pressure ranging from 0.1 to 1.0 MPa. The best results were obtained with pressure values above 0.5 MPa, which allowed for the bonding of up to 95 -100% of the glass sufaces. The third part of the fabrication process concerns the interconnection with the outside environment, which involves hole production and the introduction of tubes, to allow external access of liquids. For the hole production, a computer controlled positioning system was developed, for accurate positioning of the glass substrate in the x, y and z directions, with a precision of a few micrometers. This system guaranteed the necessary alignment of the upper and lower glass substrates, which were bonded for the encapsulation of the microchannels. The holes were made with diamond burs with a common drill. Medical catheters and scalps were used as access tubes, with epoxy resin. The characterization of the fabricated microfluidic systems was achieved by monitoring the flow of aniline aqueous solutions, which was maintained through a peristaltic pump. Reproducible results were obtained, with the production smooth and residue free microchannels, which did not present leakage and exhibited a laminar flow behavior. These results are very promising for the future application of this process in the fabrication of devices for areas such as biotechnology and chemical analysis, among others.

Neste trabalho são apresentados resultados relativos ao desenvolvimento de um processo de fabricação para a produção de sistemas de microcanais em vidro tipo borosilicato, 7059 Corning Glass. O objetivo do trabalho é implementar um processo básico, mas completo, de fabricação de sistemas microfluídicos em vidro, que possam futuramente ser aprimorados com a introdução de dispositivos ópticos e eletrônicos e de elementos microfluídicos ativos, como válvulas e microbombas, para sensoreamento e controle de fluxo. O processo de fabricação foi dividido em três grandes etapas, sendo a primeira delas, a produção dos microcanais, envolvendo processos como litografia e corrosão úmida. Nos estudos de corrosão procurou-se uma solução que permitisse a obtenção de canais com superfície uniforme e lisa, sem a produção de resíduos durante a corrosão do vidro. Os melhores resultados foram obtidos com a solução HF + HCl + H2O (1:2:3), com a possibilidade de produzir canais com até 150 µm de profundidade. A segunda etapa do processo de produção dos sistemas microfluídicos envolveu o encapsulamento dos microcanais, o que foi feito através de um processo de soldagem direta (vidro com vidro) à temperatura ambiente, com aplicação de pressão entre 0,1 a 1,0 MPa. Os melhores resultados nesta etapa envolveram pressões acima de 0,5 MPa, podendo-se obter cerca de 95 - 100% da área das lâminas soldadas. A terceira etapa do processo de fabricação engloba a interconexão com o meio externo, envolvendo a produção dos furos no vidro para entrada e saída de líquidos e a introdução dos tubos de acesso para o meio externo. Para a produção dos furos foi desenvolvido um sistema posicionador computarizado que movimenta o substrato de vidro nas direções x, y e z com precisão de alguns micrometros, garantindo o alinhamento necessário entre as duas lâminas de vidro que devem ser soldadas para encapsular os microcanais. Os furos foram feitos com broca diamantada de uso odontológico fixa em uma furadeira comum. Cateteres e scalps de uso médico foram empregados como tubos de acesso, sendo selados com resina epóxi. Os sistemas microfluídicos fabricados foram testados monitorando o fluxo de soluções aquosas de anilina, o qual foi mantido através de bomba peristáltica. Os resultados se mostraram reprodutíveis, tendo se obtido microcanais lisos e sem resíduos, sem apresentar vazamentos e exibindo regime de fluxo tipicamente laminar. Em conjunto, estes resultados mostraram-se muito promissores para desenvolvimento futuro de aplicações em áreas como Biotecnologia e Análises Químicas. / In this work, a process for the fabrication of microchannels over borlosilicate 7059 Corning Glass is presented. The main objective is to develop a simple and complete process for the fabrication of microfluidic systems over glass, that can be further improved in the future, with the integration of optical, electronic and active microfluidic devices such as valves and micropumps, for sensing and flow control. The fabrication process has three main parts. The first part is the microchannel production, which is achieved through contact-lithography and wet etching. In the etching studies, a solution that led to the fabrication of channels with uniform and smooth surfaces, without residue formation was sought. The best results were attained with a HF + HCl + H2O (1:2:3), which allow for the production of channels with depths of up to 150 µm. The second part of the fabrication process is the microchannels encapsulation, which is achieved through direct (glass-glass) bonding at room temperature, with applied pressure ranging from 0.1 to 1.0 MPa. The best results were obtained with pressure values above 0.5 MPa, which allowed for the bonding of up to 95 -100% of the glass sufaces. The third part of the fabrication process concerns the interconnection with the outside environment, which involves hole production and the introduction of tubes, to allow external access of liquids. For the hole production, a computer controlled positioning system was developed, for accurate positioning of the glass substrate in the x, y and z directions, with a precision of a few micrometers. This system guaranteed the necessary alignment of the upper and lower glass substrates, which were bonded for the encapsulation of the microchannels. The holes were made with diamond burs with a common drill. Medical catheters and scalps were used as access tubes, with epoxy resin. The characterization of the fabricated microfluidic systems was achieved by monitoring the flow of aniline aqueous solutions, which was maintained through a peristaltic pump. Reproducible results were obtained, with the production smooth and residue free microchannels, which did not present leakage and exhibited a laminar flow behavior. These results are very promising for the future application of this process in the fabrication of devices for areas such as biotechnology and chemical analysis, among others.

This thesis reports the design and development of novel voltammetric pH sensors for buffered, low-buffered and unbuffered media. pH sensors in stagnant and hydrodynamic environments were designed and developed for performing measurements using square wave voltammetry. Chapter 1 introduces the motivation of this project, the current development of electrochemical sensors, and the basic theory and techniques of electrochemistry concerned within the thesis. The existing development of carbon-based electrochemical sensors and the application of screen-printing technology in sensor fabrication are highlighted. Chapter 2 introduces the screen-printing technology and the fundamental methods of numerical simulation. In addition, reagents, equipment and software packages used in the thesis are listed in this chapter. In Chapter 3, a novel design of quinone derivative-based pH probes is presented for the application in stagnant weakly buffered media (< 1mM), based on previous studies of quinone compounds in buffered media. The results from the weakly buffered system is consistent with the results in buffered systems. To further extend the application of this design in unbuffered media, a numerical model of a pH-sensitive redox particle immobilised on an electrode was developed, which predicted that the accumulation of hydrogen ions near the electrode is the possible limiting factor for the performance of this design in unbuffered media. To develop a pH-monitoring technology for unbuffered media, Chapter 4 reports on the design, fabrication and testing of different electropolymerised-phenol derivative modified electrodes, which overcome the limitation of hydrogen ions accumulation. The results revealed that 2-(methylthio)phenol graphite resin electrodes have high accuracy (ca. 1% error) in unbuffered media, benchmarked by a commercial glass pH meter. This is the first detailed study on the v application of the economical and scalable technology in pH sensing in unbuffered environment. Chapter 5 presents a unique design of electrochemical pH sensors, free from the need to use a glass reference electrode. This design integrates a pH indicator and an internal reference electrode. Different designs of ferrocene screen-printed electrodes were tested as the internal reference electrode. The nafion-coated ferrocene screen-printed electrode showed stable peak potential in a wide pH range (pH 1 - 12) with good durability (stable in 500+ cycles of test). It was then cross connected with an alizarin electrode, forming the pH sensor free from a glass reference electrode. Chapter 6 describes novel designs of hydrodynamic pH sensors. The design of a microfluidic pH sensor modified by poly-sodium salicylate was firstly demonstrated. The sensor showed a Nernstian response in a wide pH range and, in hydrodynamic conditions, provided improved accuracy in unbuffered media compared to the stagnant state. For more convenient measurements, a novel rocking disc electrode was studied for pH sensing, modified with alizarin and poly-salicylic acid as pH indicators. The electrodes modified by both chemicals showed a Nernstian response in buffered media and the highest accuracy in unbuffered media was reached at 50 rpm.

Photomasks are the backbone of microfabrication industries. Currently they are fabricated by lithographic process, which is very expensive and time consuming since it is a several step process. These issues can be addressed by fabricating photomask by direct femtosecond laser writing, which is a single step process and comparatively cheaper and faster than lithography. In this paper we discuss about our investigations on the effect of two types of laser writing techniques, namely, front and rear side laser writing with regard to the feature size and the edge quality of the feature. It is proved conclusively that for the patterning of mask, front side laser writing is a better technique than rear side laser writing with regard to smaller feature size and better edge quality. Moreover the energy required for front side laser writing is considerably lower than that for rear side laser writing. / Singapore-MIT Alliance (SMA)

Diamond is a material with many exceptional properties. In this thesis methods for fabrication of microstructures as well as several applications of such structures in optics, microfluidics and electrochemistry are presented. A method for etching deep and highly precise gratings is described. This method was used to fabricate circularly symmetric half wave plates for use in vector vortex coronagraphs. Such coronagraphs are a very promising approach to the direct imaging of extrasolar planets. By varying the lateral etch rate of the aluminum mask during diamond etching in an inductively coupled plasma, the sidewall angle of the etched structures could be controlled. This method was used to make smooth sloped sides on a waveguide for coupling light into it. Antireflective structures that drastically reduced the surface reflection in a wavelength band between 10 and 50 µm were also fabricated. An array of boron doped diamond microelectrodes for electrochemical measurements in a microchannel was fabricated and tested, showing very good stability and reusability. Several hundred hours of use did not adversely affect their performance and no damage to them could be detected by atomic force microscopy or scanning electron microscopy. Superhydrophobic surfaces in diamond were demonstrated, using both hydrogen and fluorine termination. Hydrogen termination on a flat surface gives contact angles below 90°. To achieve a superhydrophobic surface with this low intrinsic hydrophobicity, structures looking like microscopic nail heads were fabricated. The effect of water pressure on immersed superhydrophobic surfaces was also studied and it was found that the collapse of the superhydrophobic state due to pressure was sometimes reversible as the pressure was lowered. Finally, a method was tested for functionalizing diamond surfaces using block copolymers of polyethylene oxide and polypropylene oxide to both passivate the surface and to attach synthetic binder molecules. This method was found to give very high signal to noise ratios when detecting C-reactive protein.

In this work, a MFC fabrication procedure including two non-conventional techniques (partial baking and cap-sealing) were employed for the development of an up-scaled microfluidic fuel cell (MFC). Novel carbon-based electrode materials were employed, including carbon foam, fibre, and cloth, the results from which were compared with traditionally-employed carbon paper. The utilization of carbon cloth led to 15% of the maximum power that resulted from carbon paper; however, carbon fibre led to a 24.6% higher power density than carbon paper (normalized by electrode volume). When normalized by projected electrode area, the utilization of carbon foams resulted in power densities up to 42.5% higher than that from carbon paper. The impact of catalyst loading on MFC performance was also investigated, with an increase from 10.9 to 48.3 mgPt cm-2 resulting in a 195% increase in power density.

In this work, a MFC fabrication procedure including two non-conventional techniques (partial baking and cap-sealing) were employed for the development of an up-scaled microfluidic fuel cell (MFC). Novel carbon-based electrode materials were employed, including carbon foam, fibre, and cloth, the results from which were compared with traditionally-employed carbon paper. The utilization of carbon cloth led to 15% of the maximum power that resulted from carbon paper; however, carbon fibre led to a 24.6% higher power density than carbon paper (normalized by electrode volume). When normalized by projected electrode area, the utilization of carbon foams resulted in power densities up to 42.5% higher than that from carbon paper. The impact of catalyst loading on MFC performance was also investigated, with an increase from 10.9 to 48.3 mgPt cm-2 resulting in a 195% increase in power density.

Cancer is a class of diseases in which a group of cells grow uncontrollably, destroy surrounding tissue and eventually spread to other parts of the body, often leading to death. According to the American Cancer Society cancer causes accounts for 13% of all deaths. Much of the time cancer can be treated if diagnosed early. Considerable study is currently being undertaken to investigate tissue properties and their use in detecting cancer at an early stage through non invasive and non surgical methods. Oblique Incidence Diffuse Reflectance Spectrometry (OIDRS) is one such method. This thesis reports the design, fabrication and testing of a new miniaturized optical sensor probe with "side viewing" capability for oblique incidence diffuse reflectance spectrometry. The sensor probe consists of a lithographically patterned polymer waveguides chip and three micromachined positioning substrates and source/collection fibers to achieve 45 degree light incidence and collection of spatially resolved diffuse reflectance. The probe was tested at the Mayo Clinic in Rochester Minnesota. The test results show that the probe is capable of collecting data which can be analyzed to select image features to differentiate the cancerous tissue from non cancerous tissue. Using these probes, diffuse reflectance of human esophageal surface has been successfully measured for differentiation of cancerous tissues from normal ones.

Compliant Air Foil Bearings are used in a wide variety of applications. The versatility, ease of manufacture, and low cost of foil bearings are a few of the reasons foil bearing have been so thoroughly researched. Miniaturization of gas foil bearings has been explored using silicon parts with marginal success. An approach utilizing a well known micro-fabrication technique called LIGA (German acronym meaning Lithography, Electroplating, and Molding) is suggested as an alternative method. X-ray LIGA and UV-LIGA were explored and elastic foundations 200?m and 1mm in depth were made for an impulse turbine test setup. The main difference in between the two methods is resolution and depth that each is capable of producing. In addition, precision machine forming was used to create a top foil for the foil bearing. The predicted performance of the bearing was investigated through the orbit simulation method. A parametric study based on preload, as well as loss factor, was conducted in which the rotor speed was varied and the responses were used to create cascade plots. Both the response and cascade plots are useful to determine the onset of instability and the maximum operating speed of the foil bearing manufactured through LIGA. The unique features of the gas foil bearing introduced provide great promise in terms of its application considering the high stable operating speed is just above 1000 krpm.