Contributions à l’intégration des procédés de fabrication et d'encapsulation d’un commutateur MEMS RF ohmique

Abstract : This dissertation presents studies to resolve process integration problems in the fabrication of packaged radio frequency microelectromechanical system (RF MEMS) ohmic switches with a Au-Ru contact metallurgy and Al-Ge eutectic wafer bonding for wafer-level packaging (WLP). While unpackaged RF MEMS switches have shown promising attributes poor reliability has limited their development into practical products, demanding compatibility with a hermetic sealing solution. The first article, titled ‘Exploring Ru compatibility with Al-Ge eutectic wafer bonding,’ and its supplemental material examine bond impacts associated with the refractory metal ruthenium (Ru). The compatibility of Ru with a wafer bonding process has been virtually unexplored. The main text of this section outlines the results of blanket deposition annealing experiments with Ru, Al and Ge configurations to address concerns of ternary alloy poisoning, melt wettability on Ru, and Ru as a diffusing contaminant in Al and Ge. A brief exploration of the composition process window for Al-Ge alloys contaminated with Ru is made from available phase diagrams, and strong bond outcomes with real product wafers with Ru contacts are presented. The article concludes that Ru has high compatibility within an expected narrow composition process window of marginally reduced melting temperature for Al-Ge alloy. Supplemental material addresses additional process integration problems in the real bond process associated with Ru: alumina thickening, Ru contamination and Al hillock aggravation. These are challenges for the Al surface, which progressively loses bonding ability with Ge through the fabrication process, and can be obviated with unprocessed bonding Al without Ru exposure. The second article, titled ‘Mitigating re-entrant etch profile undercut in Au etch with an aqua regia variant,’ and its supplemental material examine processed Au outcomes and bond-on-contact consequences primarily inflicted on Au. Thermally-stable Au metallization to Si for microswitch contacts in packaged devices is a considerable integration challenge. The main text of this section outlines an etch profile investigation of Au metallization stack variants with adhesion layers to discriminate delamination-based undercutting from galvanic undercutting when using an aqua regia-based solution, showing which mechanism is applicable for this etchant. A brief examination of the electrochemistry of the etchant is made to explain the unusual outcome of mitigated galvanic undercut confirmed by this analysis, with delamination control eliminating or minimizing undercut for thick Au films. In the supplemental material Au surface evolution is tracked across the fabrication process, with the wafer bonding thermal cycle being deemed most significant. Au hillocking and delamination are the primary challenges, and segmentation of Au features is a leading mitigation option that increases the impact of any Au undercut. Together these chapters develop an improved understanding of contact/bond compatibility. Necessary and promising future work for RF MEMS microfabrication and packaging is outlined at the conclusion of this dissertation.Cette thèse présente des études visant à résoudre les problèmes d’intégration de procédés dans la fabrication de commutateurs radiofréquence ohmiques de systèmes microélectromécaniques de (RF MEMS) encapsulés par une métallurgie de contact Au-Ru et un collage eutectique de gaufres Al-Ge pour l'encapsulation au niveau des gaufres (Wafer-Level Packaging, WLP). Bien que les commutateurs MEMS RF non encapsules aient montré des attributs prometteurs, leur faible fiabilité a limité leur développement en produits pratiques, exigeant la compatibilité avec une solution de collage hermétique. Le premier article, intitulé ‹‹Exploring Ru compatibility with Al-Ge eutectic wafer bonding››, et son supplément examinent les effets de liaison associés au ruthénium (Ru), un métal réfractaire. La compatibilité du Ru avec un procédé de collage de gaufres a été très par inexplorée. Le texte principal de cette section présente les résultats d'expériences de recuit des dépôts pleine plaque avec des configurations de Ru, Al et Ge pour répondre aux préoccupations concernant l'empoisonnement des alliages ternaires, la mouillabilité de la masse fondue sur le Ru, et le Ru en tant que contaminant diffusant dans Al et Ge. Une brève exploration de la fenêtre de procédé de composition pour les alliages Al-Ge contaminés par Ru est faite à partir des diagrammes de phase disponibles, et des résultats de collage fort avec des gaufres de produits réels avec des contacts Ru sont présentés. L'article conclut que Ru a une compatibilité élevée dans une fenêtre de procédé de composition étroite attendue de température de fusion marginalement réduite pour l'alliage Al-Ge. Des documents complémentaires traitent de problèmes d'intégration autres dans le procédé de collage réel associés au Ru: épaississement de l'alumine, contamination par le Ru et aggravation de la topographie d'Al. Il s'agit de défis pour la surface de l'aluminium, qui perd progressivement sa capacité de collage avec le Ge au cours du procédé de fabrication, et qui peuvent être évités avec de l'aluminium de collage non traité sans exposition au Ru. Le deuxième article, intitulé ‹‹Mitigating re-entrant etch profile undercut in Au etch with an aqua regia variant››, et son matériel supplémentaire examinent les résultats de la gravure de l'Au et les conséquences de la liaison sur le contact principalement infligées à l'Au. La métallisation thermiquement stable de l'Au sur le Si pour les contacts dans les dispositifs encapsulés est un défi d'intégration considérable. Le texte principal de cette section décrit une étude sur le profil de gravure de variantes d'empilement de métallisation Au avec des couches d'adhérence pour distinguer la sous-coupe basée sur la délamination de la sous-coupe galvanique lors de l'utilisation d'une solution à base d'eau régale, montrant quel mécanisme est applicable pour ce réactif de gravure. Un bref examen de l'électrochimie de l'agent de gravure est effectué pour expliquer le résultat inhabituel de la surgravure galvanique atténuée confirmée par cette analyse, le contrôle de la délamination éliminant ou minimisant la surgravure pour les films d'Au épais. Dans les documents complémentaires, l'évolution de la surface de l'or est suivie tout au long du procédé de fabrication, le cycle thermique de collage des gaufres étant considéré comme le plus important. La formation de bosses et le délaminage de l'or sont les principaux défis à relever, et la segmentation des caractéristiques de l'or est une option d'atténuation importante qui augmente l'impact de toute contre-dépouille de l'or. Ensemble, ces chapitres permettent de mieux comprendre la compatibilité contact/liaison. Les travaux futurs nécessaires et prometteurs pour la microfabrication et le conditionnement des MEMS RF sont présentés en conclusion de cette thèse

Fabrication and characterization of biomimetic dry adhesives supported by foam backing material

Using sacrificial templates to create 3D structures is commonly employed in various fields such as tissue engineering and water remediation to create complex and high surface area scaffolds. Herein, several sacrificial templating techniques are tried, tested, and evaluated and several methods for creating 3D porous material are discussed, including: solvent casting particulate leaching (SCPL) and simple sugar and salt leaching. The porous material is then integrated with polymer soft lithography patterning to create a single functionally graded adhesive (FGA) material to use in dry adhesive applications. The use of a soft foam backing layer helps to improve the compliance and flexibility of the adhesive pad, thus enhancing peel tolerance, buckling, and deflection and vibration resistance. A dry FGA based on film-terminated silicone foam is developed utilizing the polymer foam's capacity to absorb large amounts of energy and so deliver high adhesion and peel resistance. The fabrication technique is based on simple sugar cube templating of common elastomers, followed by film termination of the polymer cubes using the same material. Dependencies of the pull-off adhesive force and energy release rate on preload and foam thickness are systematically investigated through a series of axisymmetric indentation/de-bonding tests. The contribution of the foam backing layer to the overall compliance and adhesion is analysed and discussed. The developed elastic film-terminated structure strongly enhances the pull-off force and work of adhesion, and can be employed in the transport of delicate objects, as demonstrated in the pick and place of a silicon wafer. Furthermore, the proposed foam-based FGAs can be readily detached from the adherent surface by applying shear deformation between the pad and the surface. This research clarifies the role of mechanical graded properties in adhesion and can have technical implications in the development of a simple but effective dry adhesive material for mounting and transporting objects using automated robotic devices. The film terminated dry adhesive pads were further developed to investigate the feasibility of using a foam backing material as a universal platform to improve the adhesive properties of other terminal surface morphologies. Integrating other fast prototyping technologies as an alternative to lithographic templating techniques, scaled acrylonitrile butadiene styrene (ABS) 3D printed mushroom capped terminal structures are determined to be comparable to polyacrylate microstructure templated moulds. The effect of the foam is systematically evaluated using a similar axisymmetric indentation/de-bonding test with a probe of a large radius of curvature. Contact splitting through the control of terminal structures in both micro and millimetre scales shows improved contact properties with the addition of foam backing material. The mushroom capped adhesive pads are employed to demonstrate shear peel tolerance and cold temperature surface tolerance demonstrations. Lastly, various sugar and salt templating techniques are explored and optimized for consistency and repeatability to select the material most suitable for current research. Statistical analysis is used in the selection process. A linearly approximated model to determine the pull-off force from foam porosity and stiffness parameters are reported as sample candidates. Model estimates find that the density of sugar granules and the applied preload force are the mostly significant contributors to increasing pull-off force

3D complex shaped- dissolvable multi level micro/nano mould fabrication

There is growing interest in the development of fabrication techniques to cost effectively mass-produce high-resolution (micro/nano) 3D structures in a range of materials. Biomedical applications are particularly significant. This work demonstrates a novel technique to simultaneously fabricate a sacrificial mould having the inverse shape of the desired device structure and also create the desired device structure using electroplating deposition techniques. The mould is constructed of many thin layers using a photoresist material that is dissolvable and sensitive to UV light. At the same time the device is created in the emerging mould layers using Gold electroplating deposition technique. Choosing to fabricate the mould and the 3D structures in multiple thin layers allows the use of UV light and permits the potential cost-effective realization of 3D curved surfaces, the accuracy and geometric details of which are related to the number of layers used. In this work I present a novel idea to improve the LIGA process when using many masks to deposit multi thin layer over each other. Moreover, this technique can be utilized to produce a curved surface in the vertical direction with any diameter. Practically, a 2 µm thickness of layer is applied in the proposed technique. However, a layer of 0.5 µm or less can be deposited. An example is provided to explain the novel fabrication process and to outline the resulting design and fabrication constraints. With this technique, any structure could be made and any material used. The work employs conventional techniques to produce a 3D complex shape. By using conventional techniques with multi layers to produce a 3D structure, many problems are expected to occur during the process. Those problems were mentioned by many researchers in general but have not been addressed correctly. Most researchers have covered those problems by leaving the conventional and using a new technique they invented to produce the required product. However, in my work I have addressed those problems for the first time and I offered a new and effective technique to improve the MEMS technology and make this technology cheaper. This was achieved by using a research methodology requiring a rigorous review of existing processes, as outlined above, then by proposing a concept design for an improved process. This novel proposed process was then tested and validated by a series of experiments involving the manufacture of demo-devices. The conclusion is that this new process has the potential to be developed into a commercially implementable process