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Abstract

A CMOS digital ROIC is presented for multi-channel and differential piezo-resistive sensing, as part of the positioning system of a liquid dispensing MEMS. New very low-voltage and single-battery compatible circuit techniques are proposed for digital gain tuning, pre-amplification and A/D conversion. Also, overall low-power consumption is achieved by operating key devices in subthreshold to prevent from heating the fluidic MEMS. The complete system has been integrated in 0.35 mum CMOS 2-polySi 4-metal technology.

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Abstract

A new concept for a precise compensation of the static capacitance of piezoelectric silicon-based micromembranes is proposed. Combining analog and digital (FPGA) hardware elements with specific software treatment, this system enables the parallel excitation and detection of the resonant frequencies (and the quality factors) of matrices of piezoelectric micromembranes integrated on the same chip. The frequency measurement stability is less than 1ppm (1-2 Hz) with a switching capability of 4 micromembranes/sec and a measurement bandwidth of 1.5 MHz. The real-time multiplexed tracking of the resonant frequency and quality factor on several micromembranes is performed in different liquid media, showing the high capability of measurement on dramatically attenuated signals. Prior to these measurements, calibration in air is done making use of silica microbeads successive depositions onto piezoelectric membranes surface. The mass sensitivity in air is thus estimated at , in excellent agreement with the theoretical corresponding value.

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Abstract

The aim of this paper is to demonstrate that vibrating microcantilevers can be used to quantify fluid properties such as density and viscosity. Contrary to classical rheological measurements using microcantilevers, the development of the proposed microrheometer is based on the measurement of fluid properties over a range of vibration frequencies, without necessarily being restricted to resonant phenomena. To this end, an analytical model is implemented and, when combined with measurements, allows the determination of the viscosity as a function of frequency. The preliminary results are encouraging for the development of a useful microrheometer on a silicon chip for microfluidic applications.

Abstract

A microspotting tool, consisting of an array of micromachined silicon cantilevers with integrated microfluidic channels is introduced. This spotter, called Bioplume, is able to address on active surfaces and in a time-contact controlled manner picoliter of liquid solutions, leading to arrays of 5 to 20-¼m diameter spots. In this paper, this device is used for the successive addressing of liquid solutions at the same location. Prior to exploit this principle in a biological context, it is demonstrated that: (1) a simple wash in water of the microcantilevers is enough to reduce by >96% the cross-contamination between the successive spotted solutions, and (2) the spatial resolution of the Bioplume spotter is high enough to deposit biomolecules at the same location. The methodology is validated through the immobilization of a 35mer oligonucleotide probe on an activated glass slide, showing specific hybridization only with the complementary strand spotted on top of the probe using the same microcantilevers. Similarly, this methodology is also used for the interaction of a protein with its antibody. Finally, a specifically developed external microfluidics cartridge is utilized to allow parallel deposition of three different biomolecules in a single run.

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Résumé

Détecter un ensemble de marqueurs biologiques dans un sérum de patient ou bien des molécules spécifiques d'un herbicide dans un échantillon prélevé dans l'eau d'une rivière ? Etre capable de transformer une interaction biologique en un signal électrique ou encore déposer des volumes infiniment faibles de molécules biologiques sur une surface solide à des fins de diagnostique ? Passer de la fabrication de microcapteurs inertiels pour la navigation à la conception et au développement de biocapteurs micromécaniques ? Nous démontrons que le fil conducteur permettant de faire le lien entre ces domaines en apparence disjoints est matérialisé par des micro- et nanosystèmes électromécaniques développés au sein du LAAS à partir de la feuille blanche jusqu'à l'intégration du système avec son électronique associée. Quel lendemain pour les bio- microsystèmes électromécaniques ? Faut-il encore miniaturiser ? Est-il pertinent d'entreprendre le contraire ? Comment poursuivre l'aventure transdisciplinaire en étant sûr du fait que la réussite est au bout de la route ? Nous tentons de répondre à l'ensemble de ces questions tout au long de ce manuscrit retraçant l'ensemble de nos travaux de recherche effectués au LAAS et ailleurs depuis l'an 2000.

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Abstract

The focus of this work is a liquid dispensing system relying on the use of piezoresistive silicon microcantilevers. Experimental calibration of newly developed devices, required for global characterisation of their mechanical, electromechanical properties and other performance characteristics, is usually complicated due to structures small size as well as cost- and time-consumption. On the other hand, closed-form analytical solutions to nonlinear behaviour of devices of non-canonical geometry incorporating residual stresses are not commonly available either. Therefore, virtual calibration by means of computational modelling and simulation is not only adequate, but highly desirable. The finite element method has repeatedly proven its worth as a useful and efficient technique for the investigation of various mechanical and multiphysical systems, and has been extensively used in the design and analysis of MEMS. In the present work, the method is employed for virtual calibration of mechanical and electromechanical properties of novel liquid dispensing cantilevers. Separately, mechanical and electromechanical simulation results are in good agreement with experiment. Combined, these simulation data provide the ultimate calibration tool allowing control over the force applied by depositing devices onto the substrate and therefore preventing stiction problems and damage of fragile depositing surfaces.

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Abstract

Electrowetting is used to assist the delivery of droplets by a contact method. The electro-assisted liquid dispensing technique enables to monitor the drop size via the voltage applied between the tool, i.e. silicon cantilevers, and the deposition surface. Voltages ranging from 0 to 210 V are used to deposit water-glycerol drops with diameters and volumes in the range of 5µm-40µm and 20fL-13pL. The presented results demonstrate that electrowetting-assisted deposition is of special interest for patterning applications requiring large features to be directly and quickly written using a minimum volume of reagents.

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