A. Sayah

The introduction of powder blasting for sensor and microsystem applications

We introduce powder blasting using a pressurised nozzle and a metallic mask as a new promising technology for microsystem fabrication. We study basic parameters of this powder blasting erosion process as well as mask-geometry effects on the erosion rate. We demonstrate the application potential of this technique in three important fields of microsystems research: (i) the realisation of microfluidic chips for biochemical separations, (ii) the micropatterning of composite hard magnetic layers for mechatronic and magnetic sensor applications, and (iii) the realisation of inertial sensors in glass. We present for the first time a mechanical and electrical characterisation of powder-blasted accelerometer devices.

Biosystem for the culture and characterisation of epithelial cell tissues

Reference LMIS2-CONF-2000-002Afficher la publication dans Web of Science Notice creee le 2005-10-26, modifiee le 2017-05-10

Development of novel low temperature bonding technologies for microchip chemical analysis applications

We introduce two new low temperature bonding technologies for the assembly of microstructured glass substrates for the realisation of microchannels for miniaturised chemical analysis applications. A first method consists of a proper cleaning of the two glass surfaces, followed by a simple epoxy gluing process at 90°C. In a second method, direct bonding is obtained just by exposing the glass stack to a high pressure (up to 50 MPa) in the 100-200°C temperature range. We obtain bonding strengths as high as 10 MPa, higher than the best values obtained by HF-assisted or plasma-assisted bonding. For the realisation of the microchannels, we introduce, besides the well-known HF-etching technology, two simple alternative methods, namely, sawing and micropowder blasting.

Powder blasting for three-dimensional microstructuring of glass

We report on powder blasting as a promising technology for the three-dimensional structuring of brittle materials. We investigate the basic parameters of this process, which is based on the erosion of a masked substrate by a high-velocity eroding powder beam, using glass substrates. We study the effect of various parameters on the etching rate, like the powder velocity and the mask feature size, which induces geometrical effects to the erosion process. We introduce oblique powder blasting and investigate, in particular, sidewall effects of the micropatterned structures. A few examples of devices micromachined by powder blasting are also presented.

Modular microsystem for epithelial cell culture and electrical characterisation

We have realised a microsystem for the culture and electrical characterisation of epithelial cell layers for cell-based diagnostic applications. The main goal of this work is to achieve both cell culture and impedimetric and potentiometric characterisation on a single device. The miniaturised cell culture system enables the uses of scarce epithelial cells, as obtained from transgenic mice or from human biopsies. The device is completely modular and offers high flexibility: a polycarbonate membrane used as cell substrate is glued in between two moulded Polydimethylsiloxane (PDMS) layers to form a sandwich, which is placed between two stacks, containing the microfluidic channels and integrated measurement electrodes. The polycarbonate membrane sandwich can be removed, replaced or analysed at any time. We have characterised the impedimetric properties of our microsystem, demonstrated epithelial cell layer growth within it, and have done the initial electrical characterisation of epithelial cell layers.

Utilization of the sol–gel technique for the development of novel stationary phases for capillary electrochromatography on a chip

Capillary electrochromatography (CEC) appears ideally suited for high performance separations at small scale, i.e. on a chip. Problems with the reproducible production of the required HPLC column, but also the lack of commercially available CEC instruments have prevented many putative applicants of this promising technique from entering the field. In this paper, a fast and easy way to produce self-containing open-tubular CEC columns (C8-moieties for reversed phase applications) by the sol-gel technique is described. The corresponding chips were designed to be compatible with a commercial system for capillary electrophoresis (namely a Beckman P/ACE 5500 system with diode array detection). Method development and application hence benefited from the injection and the detection options of this setup. The separation of a mixture of three uncharged analytes (polycyclic aromatic hydrocarbons) by the chip is given as example. Under optimized conditions, the performance of the chip appeared to be comparable or better than that of capillary-based CEC columns of the same kind.

Reduction of tip–sample interaction forces for scanning near-field optical microscopy in a liquid environment

Abstract Tip-to-sample shear force distance control of a scanning near-field optical microscope (SNOM) is more critical to implement in a liquid environment than in air. The higher viscosity of the medium increases the interaction forces between the tip and the sample and may even damage the sample in the case of soft materials. In this work we measure the decrease of the quality factor of a vibrating fiber when it is immersed in water. The main loss of quality is already observed for situations where the part of the fiber dipped in the water is only a few tens of microns long. We propose a new experimental set-up which maintains a small ( Q =52, only five times smaller than in air. Topographical and near-field optical images of a soft hydrogel are obtained without inducing any damage on the observed material. Such images are impossible to obtain with a SNOM tip totally immersed in water, due to the very soft surface of the hydrogel which contains 70% of water.

Oblique Powder Blasting for Three-dimensional Micromachining of Brittle Materials

We present oblique powder blasting as a three-dimensional micromachining technology for brittle materials. Powder blasting is a microfabrication process, based on the use of a pressurised air beam containing eroding Al2O3 particles. By varying the angle of incidence of the incoming particles to a substrate, covered by a mask, one can exploit the oblique slopes of micropatterned holes and mask underetching phenomena to generate new options for three-dimensional microstructuring. We have identified and quantified the role of secondary rebounding particles in mask underetching.

Fabrication of a novel microsystem for the electrical characterisation of cell arrays

We have designed and realised a new type of microsystem for the electrical characterisation of arrays of living cells for biomedical diagnostic purposes. We have used deep plasma etching for the fabrication of microholes and micro-fluidic channels in silicon substrates. After oxidation and electrical contact fabrication, these structured silicon wafers have been anodically bonded with Pyrex wafers. The fabrication is completed by the gluing of micro-patterned polyimide foils on top of the silicon. We have tested the electrical characteristics of our microsystems using NaCl salt solutions of various molarities. We believe that our device will open new perspectives for biochemical sensor applications.

Diffractive optical elements in titanium oxide for MOEMS applications

We demonstrate a new technology for the replication of titanium oxide glass micro- and nanostructures. Diffractive optical elements, like gratings, and Fresnel lenses with structural features down to 600 nm, are replicated in polymer moulds starting from liquid glass solutions. The salient features of the TiO/sub 2/ microstructures are: a high refractive index (of the order of 1.95-1.99), excellent transparence in the visible range and photocatalytic activity under UV illumination, which induces super-hydrophilicity. The latter property is of importance for anti-fogging and self-cleaning properties of the optical structures.