This dissertation presents work involving the manufacture and analytic modeling of microcantilever parts (length-width-thickness of roughly 500-100-10 microns). The manufacturing goals were to devise a means for and demonstrate repeatable production of microcantilevers from techniques not used in the integrated-circuit field, which are the exclusive means of current microcantilever production. The production of microcantilevers was achieved via a solvent casting approach and with injection molding, which produced parts from various thermoplastic polymeric materials (amorphous, semi-crystalline, fiber- and nanoclay-filled) in a repeatable fashion. Limits of the injection molding process in terms of the thinnest cantilevers possible were examined with 2 microns being the lower bound. Subsets of the injection-molded parts were used in a variety of sensing applications, some results were successful (e.g., vapor-phase, resonance- and deflection-based sensing), while others showed poor results, likely due to experimental shortcomings (e.g., fluid-phase, deflection-based sensing). Additionally, microcantilever parts with integrated tips were injection-molded and showed to function at the same level as commercial, tipped, silicon-nitride parts when imaging an optical grating; this experimental work was the first demonstration of injection-molded parts for chemical sensing and force spectroscopy. The scientific results were (i) the derivation of a length scale dependent bending stiffness and experimental evidence showing that such an effect was observed, (ii) the development of a new microcantilever experimental mode (surface stress monitoring via microcantilever bending resonant frequencies) and experimental validation of the technique, and (iii) a new method for determining microcantilever geometry based upon measurement of a bending, lateral, and torsional mode and experimental validation of the procedure.

The objective of this research is the development of an electrically active microneedle array that can deliver biomolecules such as DNA and drugs to epidermal cells by means of electroporation. Properly metallized microneedles could serve as microelectrodes essential for electroporation. Furthermore, the close needle-to-needle spacing of microneedle electrodes provides the advantage of utilizing reduced voltage, which is essential for safety as well as portable applications, while maintaining the large electric fields required for electroporation. Therefore, microneedle arrays can potentially be used as part of a minimally invasive, highly-localized electroporation system for cells in the epidermis layer of the skin. This research consists of three parts: development of the 3-D microfabrication technology to create the microneedle array, fabrication and characterization of the microneedle array, and the electroporation studies performed with the microneedle array. A 3-D fabrication process was developed to produce a microneedle array using an inclined UV exposure technique combined with micromolding technology, potentially enabling low cost mass-manufacture. The developed technology is also capable of fabricating 3-D microstructures of various heights using a single mask. The fabricated microneedle array was then tested to demonstrate its feasibility for through-skin electrical and mechanical functionality using a skin insertion test. It was found that the microneedles were able to penetrate skin without breakage. To study the electrical properties of the array, a finite element simulation was performed to examine the electric field distribution. From these simulation results, a predictive model was constructed to estimate the effective volume for electroporation. Finally, studies to determine hemoglobin release from bovine red blood cells (RBC) and the delivery of molecules such as calcein and bovine serum albumin (BSA) into human prostate cancer cells were used to verify the electrical functionality of this device. This work established that this device can be used to lyse RBC and to deliver molecules, e.g. calcein, into cells, thus supporting our contention that this metallized microneedle array can be used to perform electroporation at reduced voltage. Further studies to show efficacy in skin should now be performed.

no / Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.Real-time diagnostics of ceramic powder injection molding using a commercial micromolding machine was performed using ultrasound. Miniature ultrasonic sensors were integrated onto the mold insert. Melt front, solidification, temperature variation and part detachment of the feedstock inside the mold cavity were observed. It has been demonstrated that ultrasonic velocity in feedstock inside the mold cavity, the ultrasonic contact duration during which the part and mold are in contact, and holding pressure can be used to assist with optimization of injection and cooling parameters to minimize energy consumption and maximize process efficiency.

Microfabrication of ceramic features has become a critical issue in realizing the miniaturization of devices. Micromolding and sintering play critical roles in fabricating micron- and submicron-sized ceramic features using nanoparticles. Developed from soft lithography, replica molding has been proven a good method to prepare micron- and submicron-sized features. However, the fidelity of the features can be compromised by incomplete feature cavity filling and feature shrinkage during the forming process. In this study, centrifuge-aided micromolding is developed to prepare micron- and submicron-sized ZnO features. By introducing a centrifugal force, the shear-thinning behavior of the suspensions is utilized, and the cavity filling process and the diffusion of trapped air out of the features are accelerated. The drying shrinkage is decreased by increasing the density of the wet nanoparticle packing from the centrifugal process. The centrifugal force improves the fidelity of all the designed features. ZnO ridges from 0.4 μm to 2 μm size and rods of 1.6 μm size are prepared successfully. The wide applicability of this strategy has been demonstrated by preparing ZrO2 features via the same method. Sintering process has a significant influence on the morphology and microstructural evolution of micron-sized ceramic features. When ceramic features decrease to much smaller sizes, such as in the micron range, the dominating sintering mechanism(s) can be different from those of the bulk at large scales. However, limited effort has been devoted to understanding the sintering behaviors. In this study, the as-prepared micron-sized ZnO ridges and rods were sintered at 950oC for different time in air atmosphere. The sintering process destructs the ZnO features via abnormal grain growth and surface roughening. Destruction prediction of features using sintering time is established based on grain growth. Feature surface roughening is further analyzed with respect to thermodynamic fundamentals. Because of the evaporation tendency during zinc oxide sintering, sintering atmosphere has a significant influence on the sintering behavior and feature fidelity. In this study, micron-sized ZnO ridge features were sintered under air and argon atmospheres. Ridge size, line edge roughness, and grain size were characterized. Quantitative calculation of sintering behaviors was performed in order to obtain fundamental understating of the micron-sized ZnO feature sintering. It is found that oxygen partial pressure is the deciding factor for the ridge feature evolution. ZnO evaporation and defects diffusion are responsible for the ZnO bulk and ridge sintering behavior differences. / Master of Science / In order to produce portable devices with small sizes, novel techniques are required to make small components, which is called microfabrication. Since ceramic materials are widely used in various electronic devices, microfabrication of small ceramic features has become an important issue. When ceramic nanoparticles are used as the raw material, the fabrication of ceramic features mainly consists of two processes: micromolding and sintering, which are the problems that this thesis focuses on. In the micromolding process, the loose nanoparticles are packed to form features with specific shapes. In the sintering process, the nanoparticles in as-prepared features are bonded into a coherent and dense feature. For the micromolding process, a suspension made from the nanoparticles is poured into a mold with as-designed feature shape, and the dry feature is obtained after a drying process. In this study, the factors that will affect the shape of the features are studied. It is found that the major factors include completeness of the filling process and shrinkage during the drying process. By completing the micromolding process in a centrifugal machine, the micromolding process is accelerated, and the shrinkage during the drying process is decreased. Both the two aspects will benefit the feature quality. By using this technique, zinc oxide ridges from 0.4 μm to 2 μm size and rods of 1.6 μm size are fabricated successfully. It is also demonstrated that this technique can be applied to other ceramic materials. Sintering process can convert packed nanoparticles into a coherent object, which can help us to obtain dense ceramic features. However, the sintering process will cause the change in feature shape. For large size ceramic bulks, the sintering theory has been well established to explain these changes. When the size of ceramic materials decreases to very small scale, such as micron size, new sintering theory is needed to explain the change of ceramic features in the sintering process. In this study, micron-sized zinc oxide ridges and rods were sintered at 950oC for different time. It was found that the sintering process will distort the shape of the zinc oxide features. Based on thermodynamic views, the corresponding new theory was established. Because zinc oxide is relatively easy to evaporate during sintering, sintering atmosphere will also affect the shape of the features. In this study, micron-sized zinc oxide ridge features were sintered under air and argon atmospheres. It was found that oxygen content was the major factor that will affect the shape change. The corresponding theory was established to explain the effect of the sintering atmosphere based on thermodynamic views.

Cette étude a été motivée par les nombreux avantages du procédé de micromoulage, qui couple la croissance électrolytique et la localisation du film avec un moule en résine épaisse. Ce procédé permet en effet la réalisation de micro-objets, dont les dimensions sont uniquement dépendantes de la résolution des techniques de lithographie employées pour définir les moules en résine. Le micromoulage permet donc de réaliser des microstructures métalliques et est compatible avec la technologie MEMS. Nous avons mis en évidence l’influence de différents paramètres expérimentaux dans le cadre de l’étude de la croissance électrolytique du samarium-cobalt en solution aqueuse dans une cellule de Hull. Cette étude nous a permis de déterminer plusieurs points de fonctionnement conduisant à des teneurs en samarium et des épaisseurs élevées : jusqu'à 50 % de samarium et plusieurs microns d’épaisseur. En outre, un certain nombre d’hypothèse ont été émises, qui lient le procédé d’élaboration et le mécanisme de croissance. Nous avons aussi réussi a montré qu’il est possible de réaliser des micromotifs de plusieurs microns d’épaisseur contenant un rapport Sm/(Sm+Co) relativement élevé (10 %) et une faible contamination en oxygène (8 %). / This study was motivated by the advantags of micromolding process, which couples the electrolytic growth and location of the film with a thick resin mold. This method makes it possible the achievement of micro-objects, the dimensions of which are only dependent on the resolution of the lithographic techniques used to define the resin molds. The micromolding can therefore produce metal microstructures and is compatible with MEMS technology. We have highlighted the influence of various experimental parameters in the context of the study of the electrolytic growth of samarium-cobalt in aqueous solution in a Hull cell. this study allowed us to identified several operating points resulting in samarium contents and high thicknesses up to 50% of samarium and several microns thick. In addition, a number of hypotheses have been put forward, which link the process of development and growth mechanism. We also successfully showed that it is possible to create micropatterns of several microns thick report containing Sm / (Sm + Co) relatively high (10%) and low oxygen contamination (8%).

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This dissertation presents an investigation of micromachined three-dimensional microelectrode arrays (3-D MEAs) targeted toward in-vitro and in-vivo biomedical applications. Current 3-D MEAs are predominantly silicon-based, fabricated in a planar fashion, and are assembled to achieve a true 3-D form: a technique that cannot be extended to micro-manufacturing. The integrated 3-D MEAs developed in this work are polymer-based and thus offer potential for large-scale, high volume manufacturing. Two different techniques are developed for microfabrication of these MEAs - laser micromachining of a conformally deposited polymer on a non-planar surface to create 3-D molds for metal electrodeposition; and metal transfer micromolding, where functional metal layers are transferred from one polymer to another during the process of micromolding thus eliminating the need for complex and non-repeatable 3-D lithography processes. In-vitro and in-vivo 3-D MEAs are microfabricated using these techniques and are packaged utilizing Printed Circuit Boards (PCB) or other low-cost manufacturing techniques. To demonstrate in-vitro applications, growth of 3-D co-cultures of neurons/astrocytes and tissue-slice electrophysiology with brain tissue of rat pups were implemented. To demonstrate in-vivo application, measurements of nerve conduction were implemented. Microelectrode impedance models, noise models and various process models were evaluated. The results confirmed biocompatibility of the polymers involved, acceptable impedance range and noise of the microelectrodes, and potential to improve upon an archaic clinical diagnostic application utilizing these 3-D MEAs.