O presente trabalho teve como foco o desenvolvimento de um software para a simulação de processos de microfabricação em substrato e de microfabricação em superfície baseado em autômatos celulares, o simMEMS. Além disso, visando a futura incorporação de ferramentas para análise das estruturas geradas pelo programa, um módulo com funcionalidades básicas para a análise mecânica de estruturas também foi desenvolvido. No que tange à microfabricação em superfície, o software desenvolvido permite simular a corrosão anisotrópica úmida do Si em KOH e deep reactive ion etching (DRIE). O simulador de corrosão úmida utiliza um autômato celular conhecido como BCA. O simulador de DRIE usa um autômato próprio. Para a simulação dos processos de microfabricação em superfície o software fornece quatro processos: deposição de filmes, corrosão de filmes, fotolitografia e planarização. Para corrosão e deposição de filmes, diversos autômatos celulares da literatura foram analisados e os resultados dessas análises é aqui apresentado. Todos os simuladores, tanto de microfabricação em superfície como em substrato, podem ser utilizados em conjunto. Isso torna o software bastante útil e capaz de simular a fabricação de um grande número de dispositivos. / The main goal of this project is the development of a software capable of simulating both surface and bulk micromachining based on a cellular automata approach. This software has been called simMEMS. In order to enable future versions of the software to also be able to analyze the structures created by the software, a module capable of running a mechanical analysis through the finite element method is also developed. simMEMS allows the user to simulate two bulk micromachining processes: wet anisotropic KOH etching and deep reactive ion etching DRIE. The wet etching simulator uses a cellular automaton known as BCA. The DRIE simulator uses an automaton developed during this project. The surface micromachining simulator allows the user to simulate four types of processes: photolithography, film deposition, film etching and substrate planarization. Several automata for the deposition and etching of films are studied and the results of this study are presented here. All processes, be they for surface or bulk micromachining, can be used on the same substrate to simulate the entire fabrication process for a large array of devices. This makes simMEMS a very useful software.

The production of magnetic materials is of great interest for use in the micro-fabrication industry. In particular, Permalloy (Ni80Fe20) is used in the production of micro-electromechanical systems (MEMS) due to its favourable magnetic properties (high relative permeability, low coercivity and high magnetic saturation). This leads to applications in devices such as inductors, transformers and micro-actuators. The electrodeposition of NiFe is also of fundamental electrochemical interest, as there is anomalous thermodynamic behaviour, with the less noble (iron) metal depositing preferentially to the more noble (nickel) metal. To enable consistent alloy deposition nickel and nickel-iron baths are currently almost exclusively based on boric acid. Boric acid has an important role in the deposition of NiFe films but its role(s) in the electro-deposition mechanism is (are) not wholly understood. Recently (2011) boric acid has been identified as a “substance of very high concern” based on the criteria established by EU chemical regulation, REACH. In anticipation of increased regulation an alternative was sought to provide a benign alternative to boric acid in the NiFe plating bath suitable for use in micro-fabrication. Initial work was performed to benchmark the performance of existing boric acid based electro-deposition baths. Cyclic voltammetry was performed, which demonstrated the deposition of nickel and nickel-iron from boric acid baths. Coulombic efficiencies up to 93 % were measured for the deposition of nickel using the electrochemical quartz crystal microbalance (EQCM) on platinum electrodes. For nickel-iron deposition control of the film composition was demonstrated on copper electrodes through varying the iron (II) concentration, current density and temperature. A citrate bath for the deposition of nickel-iron was then developed and characterised. Cyclic voltammetry was performed in these citrate baths demonstrating the deposition of nickel and nickel-iron. Optimal conditions for depositing Ni80Fe20 were demonstrated to be an elevated temperature (60 °C) with a current density of 20 mA cm-2 and a pH of 3. Using the EQCM the efficiency for nickel deposition was measured to be > 80 %. The effects of sodium saccharin and sodium dodecyl sulfate as additives were investigated; these were shown to influence morphology but not the coulombic efficiency. Decreasing the pH was shown to lower the efficiency of nickel deposition from the citrate bath. Comparisons of key properties were made between NiFe films deposited from a boric acid bath and the citrate bath developed in this work. Test structures were used to compare the strain in the films; no significant difference was found. For 2.2 μm thick Ni80Fe20 films the sheet resistance was measured using Greek cross structures as 0.078 ± 0.004 Ω/square for films deposited from the boric acid bath and 0.090 ± 0.006 Ω/square from the citrate bath. The magnetic saturation, Ms, was measured as 895 ± 66 emu cm-3 for deposits from the boric acid bath and 923 ± 111 emu cm-3 from the citrate bath. These again show no significant difference in these values within experimental error. Coercivities for these films were measured to be between 20 and 120 A m-1. In combination, this work demonstrates the development and characterisation of a new citrate based electrodeposition bath for nickel and nickel-iron. Similar chemical, electrical, mechanical and magnetic properties were found from films deposited from both baths, thus demonstrating the suitability of the citrate bath for the deposition of nickel-iron films in microfabrication.

Neste trabalho investigamos as modificações na morfologia superficial e estrutura de filmes finos de silício amorfo hidrogenado, resultantes da irradiação com pulsos ultracurtos de femtossegundos (150 fs, 775 nm e 1 kHz). Os processos de microfabricação foram conduzidos varrendo, a velocidade constante, um feixe laser com diferentes fluências (1,8 a 6,2 MJ/m2) sobre a amostra. Os espectros de transmissão apresentaram queda para amostras irradiadas, cujas imagens de microscopia eletrônica de varredura mostraram estruturas superficiais condizentes com o fenômeno de LIPSS (Laser Induced Periodic Surface Structures). Uma análise estatística das imagens de microscopia de força atômica foi realizada com um programa que identifica e caracteriza os domínios (picos) produzidos pela microfabricação. O histograma de altura da amostra irradiada com uma fluência de 3,1 MJ/m2 mostrou que a altura média dos picos produzidos é de 15 nm, menor que o centro da distribuição de alturas para uma amostra não irradiada. Porém, para fluências acima de 3,7 MJ/m2 a morfologia é dominada pela formação de agregados. Medidas de espectroscopia Raman revelaram a formação de uma fração de silício cristalino, após a irradiação com pulsos de femtossegundos, de até 77% para 6,2 MJ/m2. Determinamos ainda uma diminuição da dimensão dos nanocristais produzidos com o aumento da fluência do laser de excitação. Portanto, nossos resultados mostram que há um compromisso entre as propriedades obtidas pela microfabricação (transmissão, distribuição de picos, fração de cristalização e tamanho dos nanocristais produzidos) que deve ser levado em conta ao aplicar a técnica de microestruturação com laser de femtossegundos. / In this work we investigated surface morphology and structural modification on hydrogenated amorphous silicon (a-Si:H) thin films, resulting from femtosecond laser irradiation (150 fs, 775 nm and 1 kHz). Microfabrication processes were carried out scanning sample´s surface, at constant speed, with distinct laser fluencies (from 1.8 to 6.2 MJ/m2). A decrease was observed in the transmission spectra of irradiated samples, whose scanning electron microscopy images revealed surface structures compatible with the Laser Induced Periodic Surface Structure (LIPSS) phenomenon. A statistical analyzes of Atomic Force Microcopy images was performed using a specially developed software, that identifies and characterizes the domains (spikes) produced by the laser irradiation. The height histogram for a sample irradiated with 3.1 MJ/m2 reveals that the average height of the produced spikes is at 15 nm, which is smaller than the center of height distribution for non-irradiated sample. For fluencies higher than 3.7 MJ/m2, however, aggregation of the produced spikes dominates the sample morphology. Raman spectroscopy revealed the formation of a crystalline fraction of 77% for laser fluence irradiation of 6.2 MJ/m2, as well as a decrease in size of the produced crystals as a function of fluence. Therefore, our results indicate that there is a compromise of the sample transmission, spikes distribution, crystallization fraction and size of nanocrystals obtained by fs-laser irradiation, which has to be taken into consideration when using this material processing method.

Cancer metastasis is the critical event leading to 90% of cancer related death. Although significant improvement in our understanding on cancer metastasis has been made through years of research, the fundamental mechanism behind this process is still not fully elucidated. For cancer researchers, the “gold standard” for metastasis studies has traditionally been the use of tissue culture and mouse models. Tissue culture offers the simplest system and ease of control but is not able to recapitulate many of the features found in an in vivo tumor microenvironment. On the other hand, mouse model systems offer the most sophisticated and physiologically relevant platforms for studying cancer. However, the lack of control over the in vivo environment in these mouse models and inherent discrepancies from human physiology make results from these models difficult to be translated to clinical trials. The advancement in microfabrication techniques and cancer models developed based on these techniques has shown potential in addressing the gap between in vitro tissue culture and mouse models. Microscopic tumor microenvironments could be built in these in vitro systems to study behavior of human cancer cells. However, the expertise involved in and extra instrumentation needed for implementing these systems have prevented their widespread use by general cancer researchers. In this dissertation, we developed two simple microfabricated systems and demonstrated their application in two aspects of cancer research. The first system is a microfabricated cell patterning stencil, where paracrine signaling can be established and its impact can be measured based on cell migration. Using this tool, we investigated the interaction between melanoma and microenvironmental cells from their common metastasis target organ. Through these simple patterning techniques, we observed significant effects that a given microenvironmental cell line had on the two different melanoma lines, as well as how melanoma affected different microenvironmental cell lines. The second system, a microfluidic device, is able to present individual soluble factors to cancer cells in order to test the response of cancer cells to these physiologically relevant factors. Through this stand-alone system, we found that breast cancer metastasis is influenced by the protein molecules secreted by themselves as well as the local glucose level. Through these findings we believe that our microfabricated systems can benefit the general cancer research community in which a complicated problem can be broken down into manageable pieces and studied on a simple platform in a controlled way. Observation made through these systems can inspire general cancer researchers to form new hypotheses and eventually lead to new findings. / 2017-02-17T00:00:00Z

Carbon nanotube (CNT)/polymer composite sheets can be extremely high strength and lightweight, which makes them attractive for fabrication of mechanical structures. This thesis demonstrates a method whereby smooth, thin CNT/polymer composite sheets can be fabricated and patterned on the microscale using a process of photolithography and plasma etching. CNT/polymer composites were made from CNTs grown using chemical vapor deposition using supported catalyst growth and floating catalyst growth. The composite sheets had a roughness of approximately 30nm and were about 61¼m or 261¼m depending on whether they were made from supported catalyst grown or floating catalyst grown CNTs. The composites were patterned using an oxygen plasma as the etchant and a hard mask of silicon nitride.

My dissertation work integrates the techniques of microfabrication, micro/nanofluidics, and bioanalytical chemistry to develop miniaturized devices for healthcare applications. Semiconductor processing techniques including photolithography, physical and chemical vapor deposition, and wet etching are used to build these devices in silicon and polymeric materials. On-chip micro-/nanochannels, pumps, and valves are used to manipulate the flow of fluid in these devices. Analytical techniques such as size-based filtration, solid-phase extraction (SPE), sample enrichment, on-chip labeling, microchip electrophoresis (µCE), and laser induced fluorescence (LIF) are utilized to analyze biomolecules. Such miniaturized devices offer the advantages of rapid analysis, low cost, and lab-on-a-chip scale integration that can potentially be used for point-of-care applications.The first project involves construction of sieving devices on a silicon substrate, which can separate sub-100-nm biostructures based on their size. Devices consist of an array of 200 parallel nanochannels with a height step in each channel, an injection reservoir, and a waste reservoir. Height steps are used to sieve the protein mixture based on size as the protein solution flows through channels via capillary action. Proteins smaller than the height step reach the end of the channels while larger proteins stop at the height step, resulting in separation. A process is optimized to fabricate 10-100 nm tall channels with improved reliability and shorter fabrication time. Furthermore, a protocol is developed to reduce the electrostatic interaction between proteins and channel walls, which allows the study of size-selective trapping of five proteins in this system. The effects of protein size and concentration on protein trapping behavior are evaluated. A model is also developed to predict the trapping behavior of different size proteins in these devices. Additionally, the influence of buffer ionic strength, which can change the effective cross-sectional area of nanochannels and trapping of proteins at height steps, is explored in nanochannels. The ionic strength inversely correlates with electric double layer thickness. Overall, this work lays a foundation for developing nanofluidic-based sieving systems with potential applications in lipoprotein fractionation, protein aggregate studies in biopharmaceuticals, and protein preconcentration. The second project focuses on designing and developing a microfluidic-based platform for preterm birth (PTB) diagnosis. PTB is a pregnancy complication that involves delivery before 37 weeks of gestation, and causes many newborn deaths and illnesses worldwide. Several serum PTB biomarkers have recently been identified, including three peptides and six proteins. To provide rapid analysis of these PTB biomarkers, an integrated SPE and µCE device is assembled that provides sample enrichment, on-chip labeling, and separation. The integrated device is a multi-layer structure consisting of polydimethylsiloxane valves with a peristaltic pump, and a porous polymer monolith in a thermoplastic layer. The valves and pump are fabricated using soft lithography to enable pressure-based sample actuation, as an alternative to electrokinetic operation. Porous monolithic columns are synthesized in the SPE unit using UV photopolymerization of a mixture consisting of monomer, cross-linker, photoinitiator, and various porogens. The hydrophobic surface and porous structure of the monolith allow both protein retention and easy flow. I have optimized the conditions for ferritin retention, on-chip labelling, elution, and µCE in a pressure-actuated device. Overall functionality of the integrated device in terms of pressure-controlled flow, protein retention/elution, and on-chip labelling and separation is demonstrated using a PTB biomarker (ferritin). Moreover, I have developed a µCE protocol to separate four PTB biomarkers, including three peptides and one protein. In the future, an immunoaffinity extraction unit will be integrated with SPE and µCE to enable rapid, on-chip analysis of PTB biomarkers. This integrated system can be used to analyze other disease biomarkers as well.

This work presents membrane development applicable in nanofluidic devices. These membranes can also be termed suspended thin films, supported on two or more edges. I first discuss motivation and background for developing these structures. Then I derive the formative principles for nanofluidic systems. Following the derivation of the Navier-Stokes and Washburn equations, I discuss applying these theories to planar nanofluidic capillaries and finish the derivation by discussing the forces that drive liquid flow in nanochannels. I next discuss the membrane development process, starting with my work in static height traps, and develop the concept of analyzing nanoparticles using suspended membranes. After reviewing the lessons learned from the double-nanopore project I discuss developing an oxide layer tuned to the needs of a membrane and present the design of an adjustable membrane structure. Afterward, I discuss modeling and simulating the structure, and present a procedure for fabricating robust membranes. I then explain applying the membrane structure to form a nanofluidic pump and document the process for recording and analyzing the pumping characteristics for nanodevices. As part of the pump section I propose a theory and model for predicting the behavior of the pumps. I next present applying active membranes as nanoparticle traps. I document a quick-turn optical profilometry method for charicterizing the devices, then present experimental data involving trapping. Early results show that the device functions as a nanoparticle concentrator and may work well as a size-based trap for nanoparticles. I conclude by summarizing the main contributions made during my course of study and by providing supplemental material to guide future research.

Ce travail a été effectué dans le cadre d’études de la miniaturisation d’un cryo-réfrigérateur de type tube à gaz pulsé (TGP) et particulièrement pour mieux comprendre l’écoulement et le transfert de chaleur dans un régénérateur, l’élément clé du TGP.Nous présentons les études numérique et expérimentale du facteur de frottement et du nombre de Nusselt pour les écoulements stationnaires et continus à nombre de Reynolds modéré O(1 − 100) au sein d’un régénérateur micro-fabriqué. L’influence de la porosité et de la géométrie est étudiée. La micro-structure précisément contrôlée représente des canaux incurvés de largeur de 10, 20 et 40 μm et de profondeur de 100 à 300 μm qui forment un réseau de colonnes ayant des profiles de losanges ou sinusoïdaux. Les micro-canaux sont gravés sur un substrat de silicium par la technologie DRIE. Une technologie d’implantation de thermomètres à l’intérieur de la micro-structure de régénérateur a été développée et mise en œuvre. Les performances des micro-régénérateurs ont été étudiées selon deux approches : la première se base sur le rapport des pertes de charges dans l’écoulement et de l’efficacité du transfert thermique (NPH/NTU) ; la deuxième, sur le coefficient de transfert de chaleur globale proposé par Bejan. L’étude numérique de ces deux critères montre tout le potentiel des micro-structures proposées. / This research is done in the framework of miniaturisation of pulse tube cryocoolers studies and especially to gain a better understanding of the mass flow and heat transfert in the regenerator, which is a crucial component of these type of cryocoolers.In this work we present a numerical and experimental study of the Darcy-Weisbach friction factor and Nusselt number for a continuous and steady flow at moderate Reynolds number O(1−100) in a micro-machined regenerators. The influence of porosity from 40 to 80 % and of the geometry parameters are studied. Well-controlled microstructures represent convoluted channels of 10, 20 or 40 μm width and 100 or 300 μm depth generated by rhombic- or sinusoidal-shaped columns.The channels are etched in Silicon wafers using DRIE MEMS technology. The thermometers are integrated inside the regenerator’s micro-structure to measure the temperature evolution. The efficiency of the regenerators is estimated using two different approaches : the first, as a ratio of pressure drop losses and heat transfer efficiency (NPH/NTU) ; the second, as a volumetric heat transfer density coefficient proposed by Bejan. The numerical study of the efficiency shows theinterest of proposed micro-structures.

The need for potable water is increasing with the ever-increasing world population. Further development of fast, portable, and cost effective analytical tools is necessary in order to create diagnostic techniques capable of supporting the water needs of the world’s population. Within the last decade microfluidics and Lab-on-a-Chip (LOC) technologies have increased the portability and speed of detection for aqueous samples. Photolithography techniques serve as a cost effective fabrication tool to create LOC electrodes on the micron scale. An in-depth look at the fabrication process is undertaken in this paper in order to further the development of micro-scale detection techniques. An electrode array capable of detecting multiple targets within one aqueous sample was designed and fabricated. The electrode array was assessed for performance characteristics to determine if reproducibility is possible. The fabrication process was also detailed for a new chemical separation technique, traveling-wave electrophoresis (TWE). TWE could serve as a separation tool capable of separating out specific charged molecules for biological and chemical samples. The TWE device was assessed on the capabilities to move charged molecules.

The purpose of this research is to develop MEMS based acoustic emission sensors for structural health monitoring. Acoustic emission (AE) is a well-established nondestructive testing technique that is typically used to monitor for fatigue cracks in structures, leaks in pressurized systems, damages in composite materials or impacts. This technology can offer a precise evaluation of structural conditions and allow identification of imminent failures or minor failures that can be addressed by planned maintenances routines. AE causes a burst of ultrasonic energy that is measured as high frequency surface vibrations (30 kHz to 1 MHz) generated by transient elastic waves that are typically emitted from growing cracks at the interior of the structure. The AE sensor marketplace is currently dominated by bulky and expensive piezoelectric transducers that are wired to massive multichannel data acquisition systems. These systems are complex to operate with the need of signal conditioning units and near proximity pre-amplifiers for each sensor that demands a fairly complicated wiring requirements. Furthermore, due to the high prices of conventional AE sensors and associated instrumentation, and the current requirements in sensor volumes for smart transportation infrastructure, it is undeniable that new AE technology is required for affordable structural health monitoring. The new AE technology must deliver comparable performance at one or two orders of magnitude lower cost, size and weight. MEMS acoustic emission (AE) sensors technology has the potential to resolve several of these traditional sensor’s shortcomings with the advantage of possible integration of on-chip preamplifier while allowing substantially cost reduction due to the batch processing nature of MEMS technology. This study will focus on filling some of the major existing gaps between current developments in MEMS acoustic emission sensors and commercial piezoelectric sensors, such as sensor size, signal-to-noise ratio (SNR), cost and the possibility to conform to sharply curved surfaces. Basically, it is proposed to develop a new class of micro-machined AE sensors or sensor arrays through strategic design of capacitive and piezoelectric MEMS sensors, which will focus on optimizing the following performance aspects: Creating geometric designs to manipulate the sensor resonant frequency and to optimize Q factor under atmospheric pressure and ambient environment. Developing a strategic selection of materials according to its acoustic impedance as insulator, structure and backing material. Developing strategies to improve the signal to noise ratio SNR with and without integrated amplification/signal processing. Performing a comparison between MEMS and commercial piezoelectric sensors.