Sébastien Jiguet

Microfabrication of ceramic components by microstereolithography

Microstereolithography is a technique that allows the manufacture of small and complex three-dimensional (3D) components in plastic material. Many of the components produced by this technique are too small and too complex to be replicated by molding and, consequently, the produced components need to have adequate mechanical or chemical characteristics to be useful. Until now, the choice of materials available in the microstereolithography process was limited to plastic, with only a few photosensitive resins available. In this paper we describe new polymer/composite photosensitive resins that can be used in the microstereolithography process for manufacturing complex 3D components. These resins are based on the insertion of a high load (up to 80 wt%) of alumina nanoparticles in a photosensitive polymer matrix. The resulting composite objects can undergo a debinding and sintering step to be transformed into pure ceramic microcomponents. During this process, their shape is unaltered, but the components undergo some shrinkage. If the load of filler material in the composite resin is high enough, no deformations and no cracks can be seen in the final ceramic components. We present different examples of complex 3D structures in composite material and in pure ceramic.

Polyimide and SU-8 microfluidic devices manufactured by heat-depolymerizable sacrificial material technique

The following paper describes a sacrificial layer method for the manufacturing of microfluidic devices in polyimide and SU-8. The technique uses heat-depolymerizable polycarbonates embedded in polyimide or SU-8 for the generation of microchannels and sealed cavities. The volatile decomposition products originating from thermolysis of the sacrificial material escape out of the embedding material by diffusion through the cover layer. The fabrication process was studied experimentally and theoretically with a focus on the decomposition of the sacrificial materials and their diffusion through the polyimide or SU-8 cover layer. It is demonstrated that the sacrificial material removal process is independent of the actual channel geometry and advances linearly with time unlike conventional sacrificial layer techniques. The fabrication method provides a versatile and fast technique for the manufacturing of microfluidic devices for applications in the field of microTAS and Lab-on-a-Chip.

On-chip light sheet illumination enables diagnostic size and concentration measurements of membrane vesicles in biofluids

Cell-derived membrane vesicles that are released in biofluids, like blood or saliva, are emerging as potential non-invasive biomarkers for diseases, such as cancer. Techniques capable of measuring the size and concentration of membrane vesicles directly in biofluids are urgently needed. Fluorescence single particle tracking microscopy has the potential of doing exactly that by labelling the membrane vesicles with a fluorescent label and analysing their Brownian motion in the biofluid. However, an unbound dye in the biofluid can cause high background intensity that strongly biases the fluorescence single particle tracking size and concentration measurements. While such background intensity can be avoided with light sheet illumination, current set-ups require specialty sample holders that are not compatible with high-throughput diagnostics. Here, a microfluidic chip with integrated light sheet illumination is reported, and accurate fluorescence single particle tracking size and concentration measurements of membrane vesicles in cell culture medium and in interstitial fluid collected from primary human breast tumours are demonstrated.

Conductive SU8-silver composite photopolymer

A new electrically conductive photosensitive composite resist has been formulated and used to build micro-components. This composite material is based on the SU-8 photopolymer, an insulating negative-tone photoresist, in which silver nano-particles have been dispersed to enhance the electrical properties of the polymer. The properties of this new photosensitive composite have been characterized by optical and electrical measurements. The patterned composite structures can be obtained for a wide range of values of the electrical conductivity, by varying the powder volume fraction of the composite. The lateral resolution of the produced structures were evaluated, and depending on the patterning conditions, can be better than 5 /spl mu/m.

Ceramic microcomponents by microstereolithography

This paper describes new polymer/ceramic photosensitive resins that can be used in the microstereolithography process for manufacturing complex 3D components in composite material. These new resins contain high loads (up to 80 wt.%) of alumina nanoparticles, used as fillers in a photosensitive acrylate-based resin of low viscosity. With the nanopowder-filled resin we developed, various small polymer/alumina composite components having a real geometric complexity were produced with small manufacturing times. When using a reactive medium containing a high enough percentage of ceramic nanoparticles, no deformation or cracks are observed after debinding and sintering, even if some shrinkage occurs during these steps. This process makes it possible to manufacture a new set of micro-components in ceramic material that could be of interest for high-temperature micro-reaction technologies, or for the production of new components in the biomedical domain.

Polyimide foam-like microstructures: technology and mechanical properties

We report a process for the realization of polyimide films with custom-designed microporosity based on the heat-induced depolymerization of polyimide-embedded polypropylene carbonate microstructures. The foam-like microstructures are up to 40 µm thick and incorporate air cavities with a width ranging from 20 to 200 µm, a length up to 5 mm and a height of 20 µm. We model the mechanical stress–strain properties of the microcavities using both analytical and numerical methods. The simulation data are in good agreement with the results of nanoindentation and microcompression experiments, which show the reduction of the effective Youngs modulus from 5.77 ± 0.06 GPa for bulk polyimide to 2.51 ± 0.03 GPa for a foam-like layer.

Surface Micromachining of Polyureasilazane Based Ceramic-MEMS using SU-8 Micromolds

We describe a novel surface micromachining process for the fabrication of ceramic-type MEMS devices, such as free-standing cantilevers, that is based on the use of high-aspect ratio micromolds of SU8 and aluminum as sacrificial layer. 250μm-high and 100-1000μm-wide molds were used to confine a liquid precursor of SiC/Si3N4 based ceramics on the sacrificial layer that enables the detachment of the green body before the pyrolysis step at 1000°C. The final ceramic cantilever has dimensions ranging from 100-500μm x 1-2mm x 50μm and a smooth surface. Details of the processing, structural and material characterization such as Dynamic Rheological and Thermogravimetric Analysis under UV will be presented and compared to those found in the literature.

SU-8 as a Material for Microfabricated Particle Physics Detectors

Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the manufacturing of microstructured particle detectors. This article aims to review some emerging detector technologies making use of SU-8 microstructuring, namely micropattern gaseous detectors and microfluidic scintillation detectors. The general working principle and main process steps for the fabrication of each device are reported, with a focus on the advantages brought to the device functionality by the use of SU-8. A novel process based on multiple bonding steps for the fabrication of thin multilayer microfluidic scintillation detectors developed by the authors is presented. Finally, a brief overview of the applications for the discussed devices is given.

Development and studies of novel microfabricated radiation hard scintillation detectors with high spatial resolution

A new type of scintillation detector is being developed with standard microfabrication techniques. It consists of a dense array of scintillating waveguides obtained by coupling microfluidic channels filled with liquid scintillator to photodetectors. Easy manipulation of liquid scintillators inside microfluidic devices allow their flushing, renewal and exchange making the active medium intrinsically radiation hard. The detectors have been fabricated by photostructuration of a radiation hard epoxy resin (SU-8) deposited on silicon wafers and coupled to a multi-anode photomultiplier tube (MAPMT) to read out the scintillation light. They have been characterized by exciting the liquid scintillator in the 200 micrometers thick microchannels with electrons from a 90Sr yielding approximately 1 photoelectron per impinging Minimum Ionizing Particle (MIP). These promising results demonstrate the concept of microfluidic scintillating detection and are very encouraging for future developments.