Sébastien Jiguet
The present thesis deals with new composite photoresists for the UV-LIGA and microstereolithography microfabrication processes. The aim is to build functional 3D objects, with high aspect ratio. Two projects have been investigated in parallel for each microfabrication process. Their similitude is the use of dry or colloidal particles to prepare photosensitive formulations. The first project is focused on the well-known negative tone photoresist SU-8. This epoxy resin is used for the UV-LIGA processes, because of its high aspect ratio. As a thick photoresist, the main applications of the SU-8 are for moulding or for making inert structures (supports). However, the SU-8 structures show some cracks and unstickings of the substrate, due to the internal stress of the epoxy resin, which is the main disadvantage of the SU-8 photoresist. In order to avoid or to decrease the cracks, silica particles have been dispersed into the photosensitive matrice. The new composite photoresist is photosensitive to UV irradiations, and allows the fabrication of composite structures, which show a better adhesion on quartz, and silicon substrates, and a better sonication resistance. The SU-8 photoresist is also used for packaging applications as a non functional material, because of its electrical isolation properties. The idea to enhance its electrical conductivity comes from its high aspect ratio and the aim to microfabricate, directly, electrical structures without a moulding step. Silver particles have been used to make a photosensitive composite material, which can be applied to the UV-LIGA process. The obtained structures are electrically conductive, even at a low percolation threshold (6%vol.), and their thicknesses range up to 20 µm. It has been shown that electrodes and screens for absorbing electromagnetic waves are possible. The second project is focused on the microfabrication of 3D complex objects by microstereolithography. These objects are usually in polymer and to widen their applications to the biomedical world, alumina particles have been added to the photoresist, a photosensitive acrylate resin. Ceramic composite objects with complex form have been built by the integral microstereolithography, and their resolution is similar to the one of polymer objects. In order to obtain ceramic objects, photosensitive composite formulations need to be highly loaded in alumina powder. That induces rheological problems, such a higher viscosity, which have been overcome by modyfying the microstereolithography process. After a thermal treatment, the ceramic composite objects, highly loaded are transformed into ceramic objects without any deformations, and cracks.
EPFL2004
