The conventional medical immunoassays (ELISA/CLIA/FPIA) are not only costly (>10,000 USD), large in size (>10,000 cm3), but also require a vast number of sampling (25 £gL/well ¡Ñ 12 well) and long detection time (1~2.5 hr). To develop a biomedical microsensor for the application of portable detecting microsystem, this thesis proposes a flexural plate wave (FPW) microsensor with a novel reflection grating electrode (RGE) microstructure. Comparing to the conventional acoustic microsensors, the FPW based device has higher mass sensitivity, lower operation frequency but higher noise level. To overcome this disadvantages, this study added the RGE microstructure into the design of FPW sensor and investigated its influences on the reduction of insertion loss and noise level. By using the surface and bulk micromachining technologies, this thesis designed and fabricated FPW-based mass-sensing device with a small volume of 0.189 cm3 and a novel RGE microstructure. The main processing steps adopted in this research include six photolithoghaphies and nine thin-film depositions. In this work, a high figure-of-merit C-axial orientation ZnO piezoelectric thin-film was deposited by a commercial magnetic radio-frequency (RF) sputter system. On the other hand, the gold/chrome interdigital transducer (IDT) and RGE aluminum electrode were deposited utilizing a commercial E-beam evaporator system. For the optimization of design specifications of the FPW devices, the space of input and output IDTs, pair number of IDT, length of delay line gap and with/without RGE design were varied and investigated. Under the optimized IDT specification, the FPW microstructure presents lower central frequency (2¡ã4 MHz), insertion loss (-11 dB) and noise level (<-30 dB) than that of the FPW based microsensor without RGE microstructure. In addition, as the sampling volume of the testing DI water is equal to 1 £gL, a high mass sensitivity (-48.3 cm2/g) and short responding time (5 min) of the FPW microsensor with RGE design can be achieved in this work. The excellent characteristics mentioned above demonstrated the implemented FPW microsensor is very suitable for the applications of portable biomedical detecting microsystems.

L’utilisation de revêtements et de couches minces déposés sur substrats est très recherchée dans de nombreuses applications. Les objectifs de ces revêtements et dépôts sont multiples (améliorer la durabilité des structures, leur résistance à l’usure et à la fatigue, etc.). D'autre part, les matériaux à gradient sont également développés en vue de répondre à de nouvelles exigences fonctionnelles, comme de meilleures tenues en température, en usure, en corrosion. Pour toutes ces applications, la caractérisation de ces revêtements et de ces matériaux à gradients, afin d’en déterminer leurs propriétés (épaisseur, constantes élastiques, adhérence, contraintes résiduelles, …etc), est déterminante pour le contrôle santé des pièces et pour leur fonctionnement optimal au cours de leur utilisation. Pour caractériser ces structures, nous avons choisi d’exploiter la dispersion des ondes de surface sur une large gamme de fréquences (10 à 60 MHz). Afin d’exciter ces ondes, des capteurs MEMS de type IDT-SAW ont été réalisés à différentes fréquences couvrant la totalité de la gamme fréquentielle considérée. L’excitation quasi-harmonique a été privilégiée dans le but d’obtenir des mesures précisesde vitesses de phase. Nous avons montré les potentialités de cette approche en caractérisant premièrement des structures à couche mince allant jusqu’à 500 nm et deuxièmement des structures amorphes à gradient de contraintes. / The use of coatings and thin layers deposited on substrates is highly sought in many applications. The objectives of these coatings and deposits are multiple (improve the durability of structures, their wear resistance and fatigue, etc.). On the other hand, gradient materials are being developed to meet new functional requirements, such as a better resistance to temperature, wear and corrosion. For all of these applications, the characterization of these coatings and gradient materials, in order to determine their properties (thickness, elastic constants, adherence, residual stresses, etc…), is decisive for the health control of pieces and for their optimum operation during their use. To characterize these structures, wechose to exploit the dispersion of surface acoustic waves over a wide frequency range (10 to 60 MHz).To excite these waves, SAW-IDT MEMS sensors have been carried out at different frequencies covering the entire frequency range we considered. The quasi-harmonic excitation was preferred to obtain accurate measures of phase velocities. We showed the potential of this approach by characterizing, first, thin layers structures (500 nm) and second, amorphous structures with a stressesgradient.

Acoustic micro-sensors have already been applied in mass sensing including surface acoustic wave (SAW), flexural plate wave (FPW), thickness shear mode (TSM) and shear horizontal acoustic plate mode (SH-APM). The FPW micro-sensor is very suitable for liquid-sensing and bio-sensing applications due to the high mass-sensitivity and low phase-velocity in liquid. However, the conventional FPW micro-sensors presented a high insertion-loss (IL) and a low signal-to-noise ratio so it is difficult to combine with IC into a micro-system. To overcome these drawbacks, this study combine the Microelectromechanical System (MEMS) technology and the high C-axis orientation ZnO piezoelectric thin-film to develop a low insertion loss, low operation frequency, and high electromechanical coupling coefficient FPW device. In this study, a high C-axis orientation ZnO piezoelectric thin-film with a 20944A.U. X-Ray diffraction intensity at 34.200 degree and a 0.573 degree full width at half maximum (FWHM) was deposited by a commercial magnetic radio-frequency (RF) sputter system. The total processes of the FPW micro-sensor included five photolithography and seven thin-film depositions. In this study a low operation frequency (0.1MHz), low insertion loss (11dB to 14dB) and high electromechanical coupling coefficient (11%) FPW sensor was developed and fabricated.

Particle separation is of great interest to many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In addition, current gold standard active separation techniques are only capable of separation based on particle size; hence, separation cannot be achieved for same-size particles with different densities. In this dissertation, a sheathless acoustic-based microfluidic platform using surface acoustic wave for not only size-dependent but also density-dependent particle separation has been investigated. In this platform, two different functions were incorporated within a single microfluidic channel with varying the number of pressure node and position. The first function was to align particles on the center of the microfluidic channel without adding any external sheath flow. The second function was to separate particles according to their size or density. Two different size-pairs of polystyrene particles with different diameters (3 µm and 10 µm for general size-resolution, 3 µm and 5 µm for higher size-resolution) were successfully separated. Also, the separation of two 10 µm diameter, different-density particle streams (polystyrene: 1.05 g/cm3, melamine: 1.71 g/cm3) was successfully demonstrated. The effects of the input power, the flow rate, and particle concentration on the separation efficiency were investigated. A range of high separation efficiencies with 94.8-100 % for size-based separation and 87.2 - 98.9 % for density-based separation were accomplished. In this dissertation, an acoustic-based microfluidic platform using dual acoustic streaming for active mixing has also been investigated. The rapid and high efficiency mixing of a fluorescent dye solution and deionized water in a microfluidic channel was demonstrated with single acoustic excitation by one interdigital transducer (IDT) as well as dual excitation by two IDTs. The mixing efficiencies were investigated as a function of applied voltage and flow rates. The results indicate that with the same operation parameters, the mixing efficiency with dual-IDT design increased to 96.7 % from 69.8 % achievable with the traditional single-IDT design. The effect of aperture length of the IDT on mixing efficiency was also investigated. Additionally, the effects of the polydimethylsiloxane (PDMS) channel wall thickness on the insertion loss and the particle migration to the pressure node due to acoustic radiation forces induced by SAW have been investigated. The results indicate that as the PDMS channel wall thickness decreased, the SAW insertion loss is reduced as well as the velocity of the particle migration due to acoustic forces increased significantly. As an example, reducing the side wall thickness of the PDMS channel from 8 mm to 2 mm in the design results in 31.2 % decrease in the insertion loss at the resonant frequency of 13.3 MHz and 186 % increase the particle migration velocity at the resonant frequency of 13.3 MHz with input power of 27 dBm. Lastly, a novel acoustic-based method of manipulating the particles using phase-shift has been proposed and demonstrated. The location of the pressure node was adjusted simply by modulating the relative phase difference (phase-shift) between two IDTs. As a result, polystyrene particles of 5 µm diameter trapped in the pressure node were manipulated laterally across the microfluidic channel. The lateral displacements of the particles from -72.5 µm to 73.1 µm along the x-direction were accomplished by varying the phase-shift with a range of -180° to 180°. The relationship between the particle displacement and the phase-shift of SAW was obtained experimentally and shown to agree with theoretical prediction of the particle position.

Ce travail rentre dans le cadre de la caractérisation des couches minces, de revêtements et de surfaces fonctionnelles (épaisseur, constantes élastiques,…). Parmi les méthodes de caractérisation potentielles, les méthodes ultrasonores employant des ondes de surface sont particulièrement intéressantes. Pour ce faire, nous avons choisi d’exploiter la dispersion des ondes de surface de type Rayleigh. En effet, les ondes acoustiques de surface (SAW) de type Rayleigh se propagent à la surface d’un matériau et l’énergie véhiculée par ces ondes est confinée sous la surface dans une couche d’épaisseur de l’ordre d’une longueur d’onde. Afin de caractériser ces revêtements, il est nécessaire de travailler sur une large gamme de fréquences. D’autre part, ces couches peuvent être fragiles et transparentes, c’est pourquoi, des transducteurs interdigités (IDT) sont envisagés. Pour optimiser ce type de capteurs, et en particulier leur bande passante, il est nécessaire d’étudier différentes configurations sachant qu’il est notamment possible de faire varier le nombre d’électrodes, les dimensions des électrodes, leurs formes et leurs espacements. Enfin, pour exciter ces ondes de surface dans une large gamme de fréquence avec des niveaux de déplacement suffisants pour la caractérisation des couches minces et revêtements, la technique à double Chirp spatio-temporel basée sur des transducteurs SAW-IDT a été privilégiée. Nous avons montré les potentialités de cette approche en caractérisant premièrement des structures à couche mince métalliques d’épaisseurs de 100 nm et plus, et deuxièmement des revêtements transparents de type sol-gel. / This work is within the scope of characterization of thin layers, coatings and functional surfaces (thickness, elastic constants,…). Among the characterization methods, the ultrasonic methods using surface acoustic waves are particularly interesting. In order to do this, we chose to make use the dispersion phenomenon of Rayleigh-like surface acoustic waves. Indeed, the propagation of these waves is close to the surface of material and the energy is concentrated within a layer under the surface of about one wavelength thick. In order to characterize these coatings and structures, it is necessary to perform measurements in high frequencies. On the other hand, these coatings can be fragile and transparent, this is why in this study, SAW-IDT sensors are achieved for surface acoustic wave generation. For optimization of these SAW-IDT sensors, particularly their band-width, it is necessary to study various IDT configurations by varying the number of electrodes, dimensions of the electrodes, their shapes and spacings. Finally, to generate the surface acoustic waves over a wide frequency range with sufficient displacement amplitude for the characterization of thin films and coatings, a time-space chirp technique with SAW-IDT sensors was selected. We have shown the potential of this approach by characterizing firstly thin metallic layers, and secondly transparent coatings obtained by the sol-gel process.

The recent development of the commercially viable thin film electro-acoustic technology has triggered a growing interest in the research of plate guided wave or Lamb wave components owing to their unique characteristics. In the present thesis i) an experimental study of the thin film plate resonators (FPAR) performance operating on the lowest symmetrical Lamb wave (S0) propagating in highly textured AlN membranes versus a variety of design parameters has been performed. The S0 mode is excited through an Interdigital Transducer and confined within the structure by means of reflection from metal strip gratings. Devices operating in the vicinity of the stop-band center exhibiting a Q-value of up to 3000 at a frequency around 900MHz have been demonstrated. Temperature compensation of this type of devices has been studied theoretically and successfully realized experimentally for the first time. Further, integrated circuit-compatible S0 Lamb based two-port FPAR stabilized oscillators exhibiting phase noise of -92 dBc/Hz at 1 kHz frequency offset with feasible thermal noise floor below -180 dBc/Hz have been tested under high power for a couple of weeks. More specifically, the FPARs under test have been running without any performance degradation at up to 27 dBm loop power. Further, the S0 mode was experimentally demonstrated to be highly mass and pressure sensitive as well as suitable for in-liquid operation, which together with low phase noise and high Q makes it very suitable for sensor applications; ii) research in view of FPARs operating on other types of Lamb waves as well as novel operation principles has been initiated. In this work, first results on the design, fabrication and characterization of two novel type resonators: The Zero Group Velocity Resonators (ZGVR) and The Intermode-Coupled Thin Film Plate Acoustic Resonators (IC-FPAR), exploiting new principles of operation have been successfully demonstrated. The former exploits the intrinsic zero group velocity feature of the S1 Lamb mode for certain combination of design parameters while the latter takes advantage of the intermode interaction (involving scattering) between S0 and A1 Lamb modes through specially designed metal strip gratings (couplers). Thus both type of resonators operate on principles of confining energy under IDT other than reflection.