Véronique Conédéra

A novel fabrication method of flexible and monolithic 3D microfluidic structures using lamination of SU-8 films

The fabrication of three-dimensional (3D) microfluidic networks entirely made of SU-8 with integrated electrodes is reported. The described technology allows the fabrication of uncrosslinked SU-8 dry film on a polyester (PET) sheet and its subsequent lamination to form closed microstructures. Unlike other reported methods, transferred layers are patterned following the bonding step allowing a more accurate and simple alignment between levels than techniques using already patterned layers. Dry release of the complete polymer microstructure was demonstrated. Flexible microfluidic chips were obtained. This technique uses simple tools and no wafer bonder is used but lamination techniques which are more collective processes. Limitations in the method for layers thicker than 50 µm have been observed and are discussed. Hydraulic flow experiments have been performed to study the deformation of the cover layer which could influence adjacent flow in a three-dimensional configuration. Important deformations have been observed for layers 10 µm thick and an average pressure greater than 100 kPa. No deformations have been noted for layers with thicknesses greater than 35 µm and for average pressures up to 200 kPa. No failures occurred within the range of the experimental set-up, i.e. up to 300 kPa.

Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.

Micro-chip initiator realized by integrating Al/CuO multilayer nanothermite on polymeric membrane

We have developed a new nanothermite based polymeric electro-thermal initiator for non-contact ignition of a propellant. A reactive Al/CuO multilayer nanothermite resides on a 100 µm thick SU-8/PET (polyethyleneterephtalate) membrane to insulate the reactive layer from the silicon bulk substrate. When current is supplied to the initiator, the chemical reaction Al+CuO occurs and sparkles are spread to a distance of several millimeters. A micro-manufacturing process for fabricating the initiator is presented and the electrical behaviors of the ignition elements are also investigated. The characteristics of the initiator made on a 100 µm thick SU-8/PET membrane were compared to two bulk electro-thermal initiators: one on a silicon and one on a Pyrex substrate. The PET devices give 100% of Al/CuO ignition success for an electrical current >250 mA. Glass based reactive initiators give 100% of Al/CuO ignition success for an electrical current >500 mA. Reactive initiators directly on silicon cannot initiate even with a 4 A current. At low currents (<1 A), the initiation time is two orders of magnitude longer for Pyrex initiator compared to those obtained for PET initiator technology. We also observed that, the Al/CuO thermite film on PET membrane reacts within 1 ms (sparkles duration) whereas it reacts within 4 ms on Pyrex. The thermite reaction is 40 times greater in intensity using the PET substrate in comparison to Pyrex.

Potentialities of a new positive photoresist for the realization of thick moulds

The fabrication of MEMS by using the technique of electrodeposition inside resist moulds has known a large development in recent years. Recently, Clariant has produced a new positive photoresist, AZ 9260 (500 cps), aimed at the realization of such thick moulds. In this paper, we describe the excellent characteristics of this product through the use of our original method to control technological parameters. The most important feature of AZ 9260 photoresist is its good transparency. Current results, using a standard mask aligner, give a good aspect ratio (height-width) of up to 15 easily for 100 ?m thick moulds and up 20 occasionally and our measurement method of transparency predicts the potential realization of mould thickness up to 150 ?m in one UV exposure.

Fabrication and characterization of microlens arrays using a cantilever-based spotter

We present a quantitative study on the fabrication of microlenses using a low-cost polymer dispending technique. Our method is based on the use of a silicon micro-cantilever robotized spotter system. We first give a detailed description of the technique. In a second part, the fabricated microlenses are fully characterized by means of SEM (Scanning Electron Microscope), AFM (Atomic Force Microscopy) non contact optical profilometry and Mach-Zehnder interferometry. Diameters in the range [25-130mum] are obtained with an average surface roughness of 2.02nm. Curvature radii, focal lengths as well as aberrations are also measured for the first time: the fabricated microlenses present focal lengths in the range [55-181mum] and exhibit high optical quality only limited by diffraction behaviour with RMS aberration lower than lambda/14.

Analysis and testing of a fluidic vortex microdiode

A new design of fluidic microdiode is proposed. An initial numerical simulation of this so-called vortex microdiode allows us to understand the working principle of the diode. It is shown that the complex relationship between the inertial and viscous effects may lead to paradoxical results: as an example, an increase in the viscosity can involve an increase in the flow rate. The simulated performances, confirmed by experimental measurements with a microdiode etched by deep reactive ion etching on a silicon wafer, are compared to the performances of other microdiodes described in the literature. The efficiency of the vortex microdiode is found to be comparable to that of the Tesla microdiode, which was the most efficient microdiode. This is very encouraging, all the more so since the optimization perspectives are varied, due to a sophisticated design.

A dedicated micromachining technology for high-aspect-ratio millimetre-wave circuits

Abstract This paper presents a new technological process to implement efficient millimetre-wave passive circuits on a silicon substrate. This process associates a thick positive photoresist acting as a mould for the realization of thick conductors (several microns) with an ultra-thin dielectric membrane using only two layers (SiO 2 /Si 2 N 3.8 ) in order to reduce both dielectric and ohmic losses in the coplanar millimetre-wave circuits. Coplanar transmission lines and a band-pass filter in the 30 GHz range, featuring respectively transmission losses lower than 0.2 and 1 dB, illustrate some potentialities of this process.

Micro-deformable mirror for next-generation adaptive optical systems

Next generation giant telescopes as well as next generation instrumentation for 10m-class telescopes relies on the availability of highly performing adaptive optical systems. Different types of AO systems are currently under study, including Multi-Conjugate AO (MCAO), high dynamic range AO, and low-order AO for distributed partial correction AO. These systems require a large variety of deformable mirrors with very challenging parameters. The development of new technologies based on micro-opto-electro-mechanical systems (MOEMS) is promising for future deformable mirrors. The major advantages of the micro-deformable mirrors (MDM) are their compactness, scalability, and specific task customization using elementary building blocks. We are currently developing a MDM based on an array of electrostatic actuators with attachments to a continuous mirror on top. A high optical quality mirror is the most challenging building block for this device. The originality of our approach lies in the elaboration of a sacrificial layer and of a structural layer made of polymer materials. With this structure, very efficient planarization has been obtained: the long-distance flatness is below 0.2 μm, the print-through of localized 9μm steps is reduced to below 0.5μm and a rms roughness of 15 nm has been measured over the surface. The integration of this mirror surface on top of an actuator array is under investigation.

Low-cost multilevel microchannel lab on chip: DF-1000 series dry film photoresist as a promising enabler

We demonstrate the use of a novel dry film photoresist DF-1000 series for the fabrication of multilevel microfluidic devices by combining a standard lithography technique and lamination technology. The optimization of the technological process enables achievement of high aspect ratio structures: 7 : 1 for free standing structures and 5 : 1 for channel structures. We proved that DF films feature a low autofluorescence level, similar to that of the SU-8 resist and compatible with most lab-on-a-chip applications. The chemical stability against aggressive solvents was also investigated. Last but not least, the non-cytotoxic effect according to ISO 10993-5 on the development of L-929 mouse fibroblast cells was established. Ultimately, we showed that this low-cost material combined with multilevel lamination and UV-lithography techniques allowed the fabrication of 3D microfluidic mixers and opened the way to perform microfluidics in three dimensions.

Computer-aided response time optimization of capacitive humidity sensors

This paper presents a MATLAB code which simulates the response of capacitive humidity sensors subjected to humidity variations. The sensors have parallel electrodes and dielectric polymer-based sensitive coatings. User-defined parameters regard the geometry of the sensor, the physical chemistry of sorption in the sensitive film and the environment of the sensor. The code includes electrostatic and gas diffusion calculation. The diffusion model is based on the theory of molecule diffusion in polymer films. The confrontation of this code with finite element simulation and experimental results demonstrates its accuracy. Experiments were carried out for DVS-BCB polymer films 1.3, 1.55 and 3.5 /spl mu/m thick with various tipper electrode geometries. Although humidity sensors are dealt with in this paper, the code can be used for the optimization of capacitive sensors for other gases.