Abdeljalil Sayah

Micromachining of glass inertial sensors

We demonstrate the feasibility of a powder blasting micro-erosion process for the micromachining of accelerometer devices in glass. Using high-speed abrasive microparticles and a metal contact mask, we structure millimeter-size cantilever beams from simple glass slides. By metalizing one side of the glass substrate, we demonstrate both capacitive and piezoresistive/strain gauge detection of the vibrating cantilever mass and measure the frequency response of mechanically excited cantilever beams. We think that our approach opens new perspectives for manufacture of inertial sensing devices in a technology alternative to Si.

Microfabrication of high-aspect ratio and complex monolithic structures in glass

We present a novel approach for the realization of complex three-dimensional microstructures in brittle materials, like glass. Our technology is based on a beam of eroding powder particles, etching a masked rotating substrate. By using an oblique powder beam and mask under-etching effects, we fabricate monolithic millimeter-high microstructures with an aspect ratio of 5 to 10. This intrinsically very simple microfabrication method also allows to realize in a unique way free-standing monolithic glass microstructures, suspended over many millimeters.

Powder blasting patterning technology for microfabrication of complex suspended structures in glass

We present a powder blasting microfabrication method and realize with it complex three-dimensional and monolithic suspended microstructures in glass. We also compare the usual metal contact mask to an alternative photosensitive flexopolymer. At normal incidence of the powder beam, the obtained profiles are similar for both methods and both the metal contact mask and the flexopolymer erosion selectivity with respect to glass is ∼ 50. By controlling the underetching induced by oblique powder blasting, suspended structures are realized, using a metal contact mask directly into the substrate. These structures can be realized in a single oblique erosion step or by a two-step normal/oblique erosion process.

Borosilicate nanoparticles prepared by exothermic phase separation

Nanoparticles play an important role in chemical and biological sciences due to their ability to bind and concentrate many molecules on their surface. Polymers and silica are widely used to make nanoparticles, but efforts to make nanoparticles from borosilicate glass--which exhibits high tolerance to chemicals and solvents, combined with excellent mechanical and thermal stability--have proved unsuccessful. Here we show that borosilicate nanoparticles (100-500 nm in size) can be synthesized by simply mixing a silicon-boron binary oxide solution, prepared using non-aqueous organic solvents, with water. This induces a vigorous exothermic phase separation in which borosilicate nanoparticles burst out of a silica phase. In addition to potential applications in the life sciences, monodisperse borosilicate particles could also have applications in the production of photonic bandgap devices with high optical contrast, contrast agents for ultrasonic microscopy or chemical filtration membranes.

Precision poly-(dimethyl siloxane) masking technology for high-resolution powder blasting

Powder blasting micro-erosion is a fast and flexible technique for the micropatterning of brittle materials. We have combined 10 /spl mu/m diameter Al/sub 2/O/sub 3/ eroding particles with a new masking technique to realize the smallest possible structures with the powder blasting process (30 /spl mu/m). Our masking technology is based on the sequential combination of two polymers: 1) the brittle epoxy resin SU8 for its photosensitivity and 2) the elastic and thermo-curable poly-(dimethyl siloxane) (PDMS) for its large erosion resistance. We have micropatterned glass microstructures with aspect ratio 1 and structural details down to 20 /spl mu/m. We compare the mask size-dependent etching rate using both 1.0 and 30 jam diameter Al/sub 2/O/sub 3/ particles and find a decreasing etching rate for structures that are smaller than about 10 times the particle size. Combining SU8 with PDMS proves to be a very easy and accurate masking technology that allows exploring the fundamental dimensional limits of the powder blasting micro-erosion process.

Fabrication and Characterization of Three-Dimensional Microlens Arrays in Sol-Gel Glass

We propose a new replication process for the realization of thick microlenses in SiO2 glass with low organic content. We start by replicating an array of cylindrical micropillars made in SU-8 negative photoresist (Microchem) into poly-dimethylsiloxane (PDMS). The PDMS replica is filled with a photoresist (Clariant AZ 9260), applied to a glass substrate and soft-baked. After demoulding, we obtain cylindrical pillars that are given a dome-like shape by a thermal softening. This structure is used as a master in a second PDMS replication step. An in-house developed sol-gel glass material with low organic content is then poured in the second PDMS replica and subsequently thermally treated to obtain an array of thick, dense and crack-free microlenses. We characterize the shrinkage and the surface roughness of the microlenses. Using imaging of millimeter-size objects in an optical microscope setup, we characterize basic optical properties of the lenses, like focal length, magnification, and distribution of the light intensity around the focal plane

Accurate masking technology for high-resolution powder blasting

We have combined eroding 10 µm diameter Al2O3 particles with a new masking technology to realize the smallest and most accurate possible structures by powder blasting. Our masking technology is based on the sequential combination of two polymers:(i) the brittle epoxy resin SU8 for its photosensitivity and (ii) the elastic and thermocurable poly-dimethylsiloxane for its large erosion resistance. We have micropatterned various types of structures with a minimum width of 20 µm for test structures with an aspect ratio of 1, and 50 µm for test structures with an aspect ratio of 2.

Fabrication of microfluidic mixers with varying topography in glass using the powder-blasting process

The powder-blasting method is used to fabricate structures with a three-dimensional topography in glass using elastomeric masks. The relation between the mask opening width and the erosion depth is exploited to fabricate microstructures with varying depth in a single micropatterning step. As an application, planar three-dimensional micro-mixers were fabricated, which consist of a repeating convergent microfluidic nozzle structure. Three different designs of the micro-mixers were considered. The mixing of co-flowing laminar streams results from the generation of multiple vortices at the exit of the different convergent nozzles.

Micro-replication of optical lenses in glass using a novel sol gel technology

A new method to realize arrays of microlenses using a sol gel glass replication technology is presented. Polydimethyl-siloxane (PDMS) master structures are used for the replication of thin glass membranes, which, by an appropriate annealing procedure, result in converging lenses with positive meniscus. Hereby, we exploit PDMS - sol gel surface interactions and thickness dependent changes in composition of the sol gel solution. The lenses are realized on a circular and square like basis. We characterize the micro-lenses by an optical imaging system and measure their focal length as a function of lens thickness and size. Also lens interference effects are measured.

LF55GN Photosensitive Flexopolymer: A New Material for Ultrathick and High-Aspect-Ratio MEMS Fabrication

A growing interest in the development of thick functional structures with high aspect ratio for microelectromechanical system (MEMS) applications has triggered the investigation of several polymer materials. This paper presents LF55GN flexopolymer material as a new negative-tone photoresist to fabricate ultrathick MEMS microstructures. Up to 4-mm-thick layers are obtained using a casting method in a single photolithography step. Standard UV illumination is used to polymerize such thick microstructures in less than 1 min and with an aspect ratio up to 27. We have fabricated microstructures on rigid, flexible, and stepped substrates. Using oblique UV exposure, tilted pillars are achieved with an angle of 25deg to the substrate normal. Due to the elastomeric nature of the LF55GN flexopolymer, the microstructures can be easily deformed without causing any stress-related problems.