David Bourrier

Capillary filling in closed end nanochannels

We investigated the interactions between liquid, gas, and solid phases in the capillary filling process of closed-end nanochannels. This paper presents theoretical models without and with absorption and diffusion of gas molecules in the liquid. Capillary filling experiments were carried out in closed-end silicon nanochannels with different lengths. The theoretical and measured characteristics of filling length versus time are compared. The results show that the filling process consists of two stages. The first stage resembles the capillary filling process in an open-end nanochannel. However, a remarkable discrepancy between the experimental results and the theory without gas absorption is observed in the second stage. A closer investigation of the second stage reveals that the dissolution of gas in the liquid is important and can be explained by the model with gas absorption and diffusion.

Development of a flexible microfluidic system integrating magnetic micro-actuators for trapping biological species

A flexible microfluidic system embedding microelectromagnets has been designed, modeled and fabricated by using a photosensitive resin as structural material. The fabrication process involves the integration of micro-coils in a multilayer SU-8 microfluidic system by combining standard electroplating and dry films lamination. This technique offers numerous advantages in terms of integration, biocompatibility and chemical resistance. Various designs of micro-coils, including spiral, square or serpentine wires, have been simulated and experimentally tested. It has been established that thermal dissipation in micro-coils depends strongly on the number of turns and current density but remains compatible with biological applications. Real-time experimentations show that these micro-actuators are efficient in trapping magnetic micro-beads without any external field source or a permanent magnet and highlight that the size of microfluidic channels has been adequately designed for optimal trapping. Moreover, we trap magnetic beads in less than 2 s and release them instantaneously into the micro-channel. The actuation solely relies on electric fields, which are easier to control than standard magneto-fluidic modules.

Particle deposition onto a microsieve

The objective of the present work is to investigate experimentally the deposition of micron-sized particles onto the surface of a microsieve membrane, which consists in a thin screen with patterned circular holes. A dilute suspension of spherical, monodisperse, polystyrene particles flows at an imposed flow rate through the membrane, in a frontal filtration mode (i.e., the flow direction is perpendicular to the membrane). The particle-to-pore diameter ratio is inferior to one. The particle and flow Reynolds numbers are both smaller than 0.1 for the flow regimes investigated in the present study. The particles are non-Brownian, inertialess, and their buoyancy is negligible. Direct visualizations of the membrane are made using video microscopy. A statistical analysis of the particle deposition locations, based on an automatic processing of video images of the membrane surface recorded during the experiment, is made possible by the periodicity of the pore distribution. Experiments show the existence of two p...

First approach to the use of liquid crystal elastomers for chemical sensors

Liquid crystalline thin films elastomers that are able to bind pesticides have been developed. The synthesis involves grafting mesogen and crosslinkable groups on a polysiloxane chain in the presence of a template molecule. The molecular imprinted material is obtained after thin film deposition, UV crosslinking and washing. Experiments of readsorption of pesticide are presented. Development of a multisensor platform based on thermal and capacitive sensors is described and tests of deposition of the polymer film are presented.

Design, fabrication and characterization of a MEMS safe pyrotechnical igniter integrating arming, disarming and sterilization functions

We proposed a safe MEMS pyrotechnical igniter made of one micro igniter and three single-use electrothermal micro switches. One ON–OFF micro switch is used to arm the pyrotechnical initiator. One OFF–ON micro switch is used to disarm the pyrotechnical initiator by cutting its electrical connections from the power supply. A second ON–OFF micro switch definitively removes the pyrotechnical initiators ignition capability. Switches are based on electrothermal mechanisms and consist in breaking one electrical connection (ON–OFF switching), or micro soldering locally two electrical connections (OFF–ON switching). The ON–OFF switching based on the decomposition of GAP energetic material requires 500 mW during 30 ms. The OFF–ON switch using a O350 µm Sn/Pb ball requires a minimum of 200 mW during 5 s to create a good intermetallic layer and therefore a good electrical contact. The fabrication process of both switches and igniter is based on classic MEMS technology steps including LPCVD, PECVD, copper electro deposition and plasma etching steps. Fabrication yield reaches 99%.

Fabrication of polymer-based optical microsystem arrays suited for the active focusing of vertical laser diodes

We present a low-cost fabrication technique of a polymer-based micro-optical-electrical-mechanical systems (MOEMS) suited for the dynamic focusing of VCSELs (vertical-cavity surface-emitting lasers). A simple method based on an SU(8) double exposure is proposed for the collective integration of small footprint transparent suspended membrane arrays on vertical laser diodes. We demonstrate that this kind of MOEMS can provide under thermal actuation a vertical displacement of around 0.2 ?m W?1?over a maximal range of 8??m. As a wide range of initial gaps between the membrane and the laser source can be chosen, this approach opens new insights into the dynamic control of the VCSEL beam waist position as well as for tunable VCSEL fabrication.

Capillary Filling in Nanochannels—Modeling, Fabrication, and Experiments

While capillary filling in channels of micrometers scale is experimentally verified to obey Washburns law well, the speed of capillary filling in nanochannels is noticeably lower than described by Washburns formula. This article reports the theoretical and experimental results on capillary filling in open-end and closed-end nanochannels. Nanochannels of 45 nm and 80 nm depth, 10 μm width, were etched in silicon and bonded to a glass cover. Experiments on filling of non-electrolytic liquid in silicon nanochannels were carried out. The filling processes were observed and recorded. To estimate the influence of electrokinetics, a mathematical model to calculate the electroviscous effect was established. This model shows that the contribution of the electroviscous effect in the reduction of filling speed is small. This result also agrees well with previous theoretical work on the electroviscous effect. That means that besides the electroviscous effect, there are other phenomena that contribute to the reduction of capillary filling speed in a nanochannel, such as air bubbles formation. Experimental investigation of capillary filling in open-end and closed-end nanochannels with different lengths was performed. The filling processes of ethanol and isopropanol and the behavior of the trapped air were recorded and evaluated. Analytical models based on the continuum assumption were used to evaluate the experimental data. We observed that the filling process consists of two stages. At the initial stage, experimental data agree well with the theoretical model, but with a higher apparent viscosity. In the final stage, condensation of the liquid phase and dissolution of the gas phase lead to total filling of the nanochannel. The observed phenomena are important for understanding the behavior of multiphase systems in nanochannels.

Fabrication and characterization of a fully integrated biosensor associating microfluidic device and RF circuit

This paper presents the first results of the fabrication and characterization of a biological sensor based on two complementary parts. A microfluidic channel along with a micromachined stop-band filter are used to detect the type of fluid which flows beneath the electronic circuit. The tridimensional (3D) structure of the microstrip technology is integrated using SU8 material which thus supports the use of buried channels. Besides being a method without contact, this bio-sensor avoids evaporation, contamination, or label fixation. Changes to the cutoff frequency and attenuation allow us to differentiate three values of the salt in water concentration with a maximum variation of attenuation of 6.5%.

High-Q SU8 based above-IC inductors for RF power devices

This paper discusses quality factor Q enhancement of inductors integrated above very low resistivity substrates (under 0.1 Ω.cm). The impact of such resistivity on the performance and the ineffectiveness of patterned ground shields are presented. Consequently, for high Q purpose, we investigate solid ground shield, additional dielectric thickness, metallic ribbon section including its aspect ratio. Q values as high as 55 at 5 GHz for a total inductance value of 0.8 nH can be achieved with only 60 µm thick dielectric layer. A low cost process has been developed to integrate these inductors above RF power LDMOS devices using the SU8 photoresist as dielectric.

Soft ferrite cores characterization for integrated micro-inductors

Ferrite-based micro-inductors are proposed for hybrid integration on silicon for low-power medium frequency DC-DC converters. Due to their small coercive field and their high resistivity, soft ferrites are good candidates for a magnetic core working at moderate frequencies in the range of 5?10 MHz. We have studied several soft ferrites including commercial ferrite film and U70 and U200 homemade ferrites. The inductors are fabricated at wafer level using micromachining and assembling techniques. The proposed process is based on a sintered ferrite core placed in between thick electroplated copper windings. The low profile ferrite cores of 1.2 ? 2.6 ? 0.2 mm3 are produced by two methods from green tape-casted films and ferrite powder. This paper presents the magnetic characterization of the sintered ferrite films cut and printed in rectangular shape and sintered at different temperatures. The comparison is made in order to find out the best material for the core that can reach the required inductance (470 nH at 6 MHz) under 0.6A current DC bias and that generate the smallest losses. An inductance density of 285 nH/ mm2 up to 6 MHz was obtained for ESL 40011 cores that is much higher than the previously reported devices. The small size of our devices is also a prominent point.