Diode laser processing of PMMA and LCP materials for microsystem packaging

The thesis describes the development of laser-assisted bonding methods for assembly of microfluidic devices and MEMS packaging. A laser microwelding technique for assembly of transparent polymer substrates for fabrication of microfluidic devices was studied. The transparent PMMA substrates were bonded together using a high power diode laser system with a broad top-hat beam profile and an intermediate titanium thin film consisting of 0.7 mm diameter spots. A tensile strength of 6 MPa was achieved for this novel method which is comparable to that of the previous work in laser welding of polymers. It has been demonstrated that the method is capable of leak free encapsulation of a microfluidic channel. Furthermore, a novel laser-based method using an LCP film for packaging of MEMS, sensors and other microelectronic devices has been investigated. The results show that it is possible to use a laser based method with an LCP polymer for high quality substrate bonding applications. Glass-glass based cavities allow optical transmission and have potential applications for optical sensors and other photonic devices. For glass-glass bonding, it was shown that thin film titanium material can be used as an effective optical absorber in the laser based LCP bonding technique. Laser bonding of glass and silicon using an LCP film has also been achieved but in this case the silicon substrate acted as the absorber to capture the laser power. Laser bonding of a silicon cap to a molded LCP package has also been demonstrated successfully. The results of temperature monitoring using embedded sensors show that the temperature at the base of the LCP package (~130C) is substantially lower than the bonding temperature (> 280C). The results of shear and leak test show good reliability and hermeticity of the laser bonded microcavities. Both two-dimensional and three-dimensional models of heat transfer are developed and studied using the COMSOL Multiphysics software tool to understand the localised laser heating effects. The results are in good agreement with those of the practical work

Laser-based packaging of micro-devices

In this PhD thesis the development of laser-based processes for packaging applications in microsystems technologies is investigated. Packaging is one of the major challenges in the fabrication of micro-electro-mechanical systems (MEMS) and other micro-devices. A range of bonding processes have become established in industry, however, in many or even most cases heating of the entire package to the bonding temperature is required to effect efficient and reliable bonding. The high process temperatures of up to 1100°C involved severely limit the application areas of these techniques for packaging of temperature sensitive materials. As an alternative production method, two localised heating processes using a laser were developed where also the heat is restricted to the joining area only by active cooling. Silicon to glass joining with a Benzocyclobutene adhesive layer was demonstrated which is a typical MEMS application. In this laser-based process the temperature in the centre of the device was kept at least 120°C lower than in the bonding area. For chip-level packaging shear forces as high as 290 N were achieved which is comparable and some cases even higher than results obtained using conventional bonding techniques. Furthermore, a considerable reduction of the bonding time from typically 20 minutes down to 8 s was achieved. A further development of this process to wafer-level packaging was demonstrated. For a simplified pattern of 5 samples the same quality of the seal could be achieved as for chip-level packaging. Packaging of a more densely packed pattern of 9 was also investigated. Successful sealing of all nine samples on the same wafer was demonstrated proving the feasibility of wafer-level packaging using this localised heating bonding process. The development of full hermetic glass frit packaging processes of Leadless Chip Carrier (LCC) devices in both air and vacuum is presented. In these laser-based processes the temperature in the centre of the device was kept at least 230°C below the temperature in the joining region (375°C to 440°C). Testing according to MIL-STD-883G showed that hermetic seals were achieved in high yield processes (>90%) and the packages did withstand shear forces in excess of 1 kN. Residual gas analysis has shown that a moderate vacuum of around 5 mbar was achieved inside the vacuum packaged LCC devices. A localised heating glass frit packaging process was developed without any negative effect of the thermal management on the quality of the seal

Mécanismes de collage et de transfert de films monocristallins dans des structures à couches de polymères

Les matériaux polymères sont à l'heure actuelle peu considérés dans le vaste domaine des micro et nano technologies. Ils présentent toutefois certaines propriétés remarquables en comparaison des matériaux traditionnels de la microélectronique. Par exemple leur déformabilité et leur légèreté permettent d'envisager des fonctions de supports flexibles pour des composants électroniques. Par ailleurs, ils offrent des solutions d'assemblage de matériaux de diverses natures. Cette étude porte précisément sur ces deux thématiques. En premier lieu, nous avons étudié les mécanismes de collage impliqués dans l'assemblage de substrats de type silicium par une couche de polymère. D'autre part, nous avons proposé des modèles de mécanisme de transfert de films monocristallins sur polymère. Les propriétés mécaniques des matériaux considérés, principalement du silicium monocristallin et des polymères de type vitreux et caoutchoutique, ainsi que leurs épaisseurs, peuvent varier sur plusieurs ordres de grandeur selon la configuration considérée. L'originalité de l'étude est de déterminer et d'aborder des configurations expérimentalement favorables, par des modèles mécaniques simples, élaborés à partir de lois d'échelle. Nous avons proposé, dans un premier temps, ces modèles pour expliquer des résultats liés à des configurations particulières et ainsi démontrer la pertinence de cette approche. Le cœur de notre étude porte sur le transfert de films monocristallins, aussi fins qu'une centaine de nanomètres d'épaisseur, sur polymère par adaptation du procédé Smart-CutTM (transfert par implantation ionique et fracture). En comparaison d'une configuration standard de cette technologie, nous avons notamment étudié l'impact des propriétés mécaniques propres aux polymères (de types vitreux ou caoutchoutique). Les méthodes en loi d'échelle nous ont ainsi permis de proposer des mécanismes de transfert, de l'échelle du nanomètre jusqu'à la fracture macroscopique. Nous avons également exposé un exemple d'application concret par la réalisation d'objets microélectroniques modèles sur et dans un film monocristallin de silicium. La structure, composée d'un film de quelques micromètres d'épaisseur supporté par un polymère, constitue ainsi une structure flexible d'un point de vue mécanique.Polymers are little considered at the moment, in the wide domain of micro- and nano- technologies. They present however certain remarkable properties by comparison with the materials used in microelectronics. For example their flexibility and their lightness allow thinking to polymers as flexible supports for microelectronic components. Besides, they offer solutions for assembling various materials.This study concerns exactly these two items. First of all, we studied bonding mechanisms implied in the assembly of silicon wafers via polymer layers. Then we proposed models for mechanism of single-crystalline layer transfers onto polymers. The mechanical properties of the considered materials (mainly single-crystalline silicon and glassy or rubber polymers) as well as their thicknesses can vary on several orders of magnitude according to the application.The originality of the study is to determine favorable experimental configurations, by simple mechanical models developed from scale laws, and to realize demonstrators. The heart of our study concerns the transfer of single-crystalline layers as thin as about hundred nanometers onto polymers by tuning of the Smart-CutTM technology (based on ion implantation and splitting for transfer). By comparison with a standard configuration of this technology, we studied the impact of the specific mechanical properties of polymers (glassy or rubber types). The methods in scale laws allowed us proposing transfer mechanisms, from the nanometer scale up to the macroscopic one. Finally we reported on a realization of micro-technology devices, made in and on single-crystalline thin silicon membranes. The stacked structures, consisting in silicon membranes thick of a few micrometers supported by polymer films, may be considered as very flexible structures.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF