Length-extension LGS microresonators for FM-AFM: microfabrication and shear effects sensitivity

Conférence internationale avec proceeding : poster 2014 IEEE International Frequency Control Symposium Taipei International Convention center. Taipei, Taiwan - 19-22 mai 2014Length extension LGS resonators have already been studied in order to make probes for frequency-modulation atomic force microscopy. Theoretical investigations are conducted on the design of the probes to improve the resolution of the microscope. Comparison of quartz and LGS crystal performances can be made using these theoretical results. The microfabrication of LGS resonators by chemical etching is proved. A monolithic length extension resonator with a tip at its end is obtained which constitutes a real advantage in regard to the existing piezoelectric probes

Homogénéisation de l'écoulement dans une cellule de Hele-Shaw et caractérisation par µPIV en champ large

Dans les capteurs biologiques basés sur la microfluidique, l'analyte d'intérêt est en général amené en contact avec une surface fonctionnalisée où il est capturé. Cette surface est ensuite analysée par mesure optique (SPR...) ou acoustique (QCM...), permettant ainsi de quantifier précisément les analytes présents dans le liquide. Notre groupe développe des capteurs acoustiques à base de membranes résonantes couplées qui sont agencées en matrice pour augmenter la sensibilité du capteur. Cette architecture nécessite l'utilisation d'une grande chambre d'analyse, de l'ordre de 1cmx1cm, où les écoulements doivent être contrôlés pour garantir une bonne homogénéité des débits sur l'ensemble de la surface du capteur lors de l'insertion ou du renouvellement des fluides dans la cavité. On limite ainsi les écarts de traitement lors des réactions de fonctionnalisation, de capture, d'inactivation ou encore lors des étapes de nettoyage de la surface de capture. Il est dès lors nécessaire de concevoir des puces microfluidiques où la géométrie et les caractéristiques des fluides permettent un écoulement homogène sans zone morte ou zone de recirculation au sein de la chambre. Ainsi nous avons étudié différentes géométries de canaux d'entrée et de sortie dans une chambre microfluidique de grande surface et de faible profondeur, à travers des simulations par éléments finis en 2D et par le développement d'un banc expérimental de caractérisation d'écoulements. Pour minimiser le volume de l'échantillon à analyser et pour faciliter la diffusion des bio-analytes vers la surface d'interaction, nous avons fixé la hauteur de la chambre à 80µm. Dans ces conditions, nous nous plaçons dans un régime d'écoulement laminaire et la cavité microfluidique peut être assimilée à une cellule de Hele-Shaw de 1cm x 1cm de côté. La simulation des écoulements par éléments finis de ces structures a été faite sous COMSOL en utilisant le modèle laminaire 2D avec approximation de faible profondeur, qui correspond bien à l'écoulement de Hele-Shaw. Nous avons étudié 5 configurations différentes en faisant varier le nombre et l'espacement des canaux d'alimentation (1 entrée/1 sortie, 16 entrées/1 sortie, 16 entrées/16 sorties) et la géométrie de la chambre (carrée, losange, bézier). L'objectif de vitesse moyenne dans la chambre était de 200µm/s et l'uniformité de l'écoulement a été évaluée en observant le profil de vitesse dans différentes sections. Pour l'étude expérimentale, les dispositifs microfluidiques ont été réalisés par microfabrication en salle blanche. Les canaux fluidiques et la chambre sont structurés dans un substrat de silicium par gravure chimique KOH puis la chambre est refermée par collage anodique d'un substrat de verre autorisant l'observation optique.  La mesure expérimentale des vitesses d'écoulement a demandé de concevoir un nouveau banc de µPIV permettant l'observation sur un champ d'un cm², tout en visualisant, en lumière blanche, des particules de faible taille. Ces particules en mélamine ont un diamètre de 920 nm pour répondre aux contraintes de sédimentation et de non modification des écoulements. La mesure locale du champ de vitesse est obtenue par corrélation entre des paires d'images espacées de 50ms, puis en faisant une moyenne sur 100 paires d'image. Nous présenterons dans l'exposé la comparaison entre les résultats expérimentaux et numériques pour les différentes chambres étudiées, qui montrent que l'on peut améliorer, en fonction de la configuration de la chambre, l'homogénéité des écoulements d'un facteur d'environ 5 sur 80% de la section

High Sensitive Mass Detection using GaAs Coupled Micro Resonators

This work demonstrates the improvement of mass detection sensitivity and time response using a quite simple structure of sensor. Indeed, complicated technological processes are often required to reach high sensitivity when we want to detect specific molecules in biological fields. These developments constitute an obstacle to the early diagnosis of diseases. An alternative is the design of coupled structures. The device is based on the piezoelectric excitation and detection of two GaAs micro struThis work demonstrates the improvement of mass detection sensitivity and time response using a quite simple structure of sensor. Indeed, complicated technological processes are often required to reach high sensitivity when we want to detect specific molecules in biological fields. These developments constitute an obstacle to the early diagnosis of diseases. An alternative is the design of coupled structures. The device is based on the piezoelectric excitation and detection of two GaAs micro structures vibrating on antisymmetric modes. GaAs is a piezoelectric material which has the advantage to be micromachined easily using clean room processes. Moreover, we showed its high potential in direct biofunctionalisation to be used in biological field1. A specific design of electrodes (three electrodes) was performed to improve the detection at low mass and an original detection method has been developed. The principle is to exploit the variation in amplitude at a fixed frequency when we are concerned by a weak frequency shift of the resonance peak. The three electrodes are geometrically identical. We excited the device at the resonance frequency, corresponding to maximum voltage of the initialization electrode. Thus we noted the voltage on the measuring electrode, which had, in the vicinity of weak added mass, the greatest slope. Therefore, we get a very good resolution for an infinitely weak mass: relative voltage variation of 8%/0.1fg. The analysis given in this paper is based on results obtained by finite element modeling

Towards the miniaturization of (hhl) resonant sensors for biochemical and environmental applications

International audienceTowards the miniaturization of (hhl) resonant sensors for biochemical and environmental application

GaAs resonant biosensor: Theoretical results, micro-fabrication and tests

International audienceGaAs resonant biosensor: Theoretical results, micro-fabrication and test

Micro structuration of GaAs surface by wet etching : towards a specific surface behavior

International audienceResonant microelectromechanical systems are promising devices for real time and highly sensitive measurements. The sensitivity of such sensors to additional mass loadings which can be increased thanks to the miniaturisation of devices is of prime importance for biological applications. The miniaturisation of structures passes through a photolithographic process and wet chemical etching. So, this paper presents new results on the anisotropic chemical etching of the gallium arsenide (GaAs) crystal used for this application, in several solutions. This paper focuses on the micro/nanostructuration of the sensing surface to increase the sensor sensitivity. Indeed, this active surface will be biofunctionalized to operate in biological liquid media in view of biomolecules detection. Several experimental conditions of etching bath composition, concentration and temperature were examined to obtain a large variety of geometrical surfaces topographies and roughness. According to the orientation dependence of the chemical etching process, the experiments were also performed on various GaAs crystal plates. The bath 1 H3PO4:9 H2O2:1 H2O appeared to be particularly adapted to the fabrication of the GaAs microstructured membrane: indeed, the bath is highly stable, anisotropic, and, as a function of temperature, it allows the production of a large variety of GaAs surface topographies

Higher-order Lamb waves with quasi-zero surface displacement components on a GaAs piezoelectric plate

International audienceHigher-order Lamb waves with quasi-zero surface displacement components are reported on (100)-cut GaAs propagating along the <110> direction where the total displacement at the surface of the plate is less than 10% of the maximum total displacement. The dispersion curves and the displacement component profiles show the reduction of total displacement at the surface of the plate starting when the phase velocities of the higher-order modes are crossing the shear bulk acoustic wave velocity to the value as low as 5%. Due to the concentration of acoustic energy inside the plate, the reported quasi-zero plate acoustic waves (QZ-PAW) further reduce the radiation of acoustic energy when the plate surface is in contact with liquid. The experimental results validate the occurrence of QZ-PAW with a reduction of viscous damping insertion loss compared to previously reported quasi-longitudinal Lamb waves. The results demonstrate the potential QZ-PAW mode for emerging applications such as dual-mode PAW sensors, PAW devices with integrated sensor and actuator, thin-film and ultra-high frequency PAW sensors in highly viscous liquid media

Gallium arsenide bulk acoustic wave sensor for biological molecules detection

International audiencePiezoelectric devices are very attractive for biosensor applications due to their high sensitivity and time stability. Several materials are used but up to now quartz remains the reference material for piezoelectric resonant sensors. GaAs crystal constitutes a good example of material that combines piezoelectric properties and advanced MEMS technology. Moreover, the possibility to directly bio-functionalize GaAs surfaces with molecules like thiolates was proved. Several results on sensors sensitivity and on GaAs biofunctionalization are shown

Langasite as a piezoelectric material for near-field microscopy resonant cantilevers

International audienceQuartz length-extension resonators have already been used to obtain atomically-resolved images by frequency-modulation atomic force microscopy. Other piezoelectric materials such as gallium orthophosphate (GaPO4), langatate (LGT), and langasite (LGS) could be appropriate for this application. In this paper, the advantages of langasite crystal are presented and the fabrication of similar microsensors in langasite temperature-compensated cuts by chemical etching is proved. A monolithic length extension resonator, with a tip at its end, is obtained which constitutes a real advantage in regard to the existing quartz devices

Specificity and Sensitivity Characterization of a Gallium Arsenide Resonant Bio-Sensor

International audienceThe characterization of the performances of a Gallium Arsenide (GaAs) based biosensor, in terms of sensitivity and specificity, is reported. The design of the sensor consists in a resonant membrane fabricated in GaAs crystal that operates at shear modes of bulk acoustic waves generated by lateral field excitation. The transducer element was fabricated by using typical clean room microfabrication techniques. The backside of the membrane is functionalized by a self-assembled monolayer (SAM) of alkanethiols to immobilize bio-receptors, which will allow the specific capture of the analyte of interest. The theoretical sensitivity of the sensor had been determined by modeling at 0.1ng. Hz-1. The operation of the device was experimentally evaluated using lymphocyte-activation protein 3 (LAG 3), simulating a real biological model for detection. As a proof of concept, the ability of the sensor to specifically detect and quantify proteins has been demonstrated