In this thesis, the c-axis-oriented AlN films were deposited on piezoelectric substrates, lithium niobate (LiNbO3), ST-Quartz, and non-piezoelectric substrate, silicon (Si), by reactive rf magnetron sputtering. AlN films were deposited with the nitrogen concentration (N2/Ar+N2) of 20¡ã80%, the chamber pressure of 1¡ã15mTorr, the rf power of 200¡ã450W, the deposition time of 1~3 hours and the substrate temperature of 100¡ã400¢J. The correlation between growth parameters and piezoelectric coefficients will be investigated by XRD¡Bd33 and K2 analysis in this study. The experimental results showed that the values of d33 become larger as the intensity of X-ray is stronger. It can also be concluded that the smaller the FWHM of (002) XRD peak is, the larger the value of d33 is. With various sputtering parameters, the K2 values exhibit diversely. The multilayer structures of AlN/LiNbO3 and AlN/ST-Quartz both make lower values of K2. In general, by combining the higher K2 and d33 values of LiNbO3 and ST-Quartz with high wave velocity of AlN, the high-frequency with high performance SAW devices can be obtained.

Le coefficient de couplage électromécanique (CCEM) est un paramètre essentiel pour la description des matériaux piézoélectriques, il traduit la conversion d’énergie électrique en énergie mécanique et vice versa. Ce coefficient de couplage est étudié et déterminé dans le cadre de cette thèse pour des céramiques piézoélectriques. Ces dernières sont utilisées pour trois structures différentes ; la première structure étudiée est constituée d’une poutre longue et mince avec des petits patchs collés symétriquement sur les deux faces de la poutre en Aluminium, la seconde structure se compose d’une poutre courte et épaisse avec deux grands patchs. La dernière structure étudiée est une plaque composite multicouche du type aéronautique avec un seul grand patch. Ces trois structures ont été étudiées afin de déterminer le coefficient de couplage électromécanique effectif qui est considéré comme un indicateur de performance de l’amortissement passif shunté. Ce coefficient de couplage a été évalué de différentes manières en utilisant différents paramètres dont les conditions limites électriques, les propriétés élastiques des patchs, les propriétés modales de la poutre seule ainsi que les facteurs de couplages piézoélectriques. Une première étude expérimentale a été menée sur la poutre longue pour deux types de configurations en court circuit et circuit ouvert pour identifier ses propriétés modales. La poutre longue a été simulée pour deux types de polarisations, identiques et opposées, et simulée dans les deux codes Ansys® et Abaqus®. L’influence de la condition d’équipotentielle sur le coefficient de couplage a été étudiée. Une seconde campagne expérimentale et numérique sur une autre structure a été nécessaire pour valider les résultats obtenus. Pour pouvoir atteindre cet objectif, il était nécessaire de travailler sur une structure plus courte et plus rigide. Ainsi, la poutre courte a été simulée dans Ansys® et les résultats obtenus ont confirmé la nécessité de prendre en compte l’équipotentialité sur les faces des patchs. Cette condition a pour effet de réduire le couplage électromécanique et parfois de découpler certains modes. L’écart résultant de la corrélation expérimentale / numérique des deux poutres instrumentées a incité à recaler les modèles numériques. Ce recalage peut se présenter sous trois formes : mécanique en remplaçant l’encastrement par des ressorts linéaires, électrique en remplaçant les capacités fournies par le fabricant par les valeurs mesurées expérimentalement et électromécanique en utilisant les deux recalages précédents simultanément. Les deux poutres ont ensuite été simulées en déformations planes et contraintes planes et recalées afin d’approcher les résultats expérimentaux. L’étude de ces deux structures a permis de confronter les différentes méthodes d’évaluation du CCEM effectif, d’évaluer l’influence de l’équipotentialité sur les faces des électrodes et de comparer les simulations bidimensionnelles aux tridimensionnelles. Une plaque composite multicouche du type aéronautique a été ensuite étudiée pour généraliser la méthode d’évaluation du CCEM effectif pour les structures minces composites. La plaque seule a d’abord été simulée dans Ansys® pour valider le modèle numérique. Des tests sur la structure adaptative ont ensuite été menés pour l’évaluation du CCEM expérimental. La position choisie du patch a été déterminée par une analyse de l’énergie de déformation de la plaque seule pour les modes d’intérêt. Cette méthode de placement du patch s’est avérée efficace dans le sens où elle a conduit à des CCEM effectifs élevés pour certains modes de la bande de fréquence retenue. / The electromechanical coupling coefficient (EMCC) is an important parameter for the description of piezoelectric materials; it measures the conversion of electrical energy into mechanical one and vice versa. The coupling coefficient is studied and determined in this dissertation for piezoelectric ceramics. The latter are used for different structures: the first studied one is a long and thin Aluminium beam with small patches bonded symmetrically on its faces, the second one is a short and thick Aluminium beam with symmetrically bonded two large patches, and the third structure is considered more complex because it is an aeronautic-type multilayer composite plate with a single large patch. These three structures were studied to determine the electromechanical coupling coefficient which is considered as a performance indicator for passive shunted damping. The coupling coefficient was evaluated in different ways using different parameters, including the electrical boundary conditions, the elastic properties of the patches, the modal properties of the base beam and the piezoelectric coupling factor. A first experimental study was conducted on the long beam for two configurations, short circuit and open circuit, to identify its modal properties. The long beam was simulated for two configurations of polarization, same and opposite, in Ansys® and Abaqus® commercial codes. The equipotential condition influence on the coupling coefficient has been studied. A second experimental and numerical campaign for a different structure was necessary to validate the obtained results. For this purpose, it was necessary to work on a shorter and more stiff structure. Thus, the short beam was simulated in Ansys® which results have confirmed the necessity to consider the equipotentiality of the patches faces. This condition was found to reduce the electromechanical coupling and to uncouple some modes. The difference between experimental and numerical results of both adaptive structures was reduced by updating the numerical models. This updating is made in three ways: mechanically, by replacing the theoretical clamp conditions by linear springs, electrically, by replacing the capacities provided by the supplier by the experimental measured values, and electromechanically by considering previous updatings simultaneously. Both beams were simulated in 2D plane-strain and plane-stress and updated in order to approximate the experimental results. The study of these two structures allowed to assess different methods for the evaluation of the EMCC, to evaluate the influence of the equipotentiality constraints on the electroded faces, and to compare two-dimensional simulations to three-dimensional ones. Finally, an aeronautic-type multilayer plate composite has been studied in order to generalize the evaluation method of the EMCC for thin composite structures. The base plate was first simulated in Ansys® in order to validate the numerical model, then tests of the adaptive plate were conducted in order to evaluate the experimental EMCC. The selected position of the patch results from a strain energy analysis of the base plate for the mode of interest. The patch placement method was efficient in the sense that it provided high EMCC for some modes in the retained frequency range.

Abstract Compared with the other micro acoustic wave devices, the flexural plate-wave (FPW) device is more suitable for being used in liquid-sensing applications due to its higher mass sensitivity, lower phase velocity and lower operation frequency. However, conventional FPW devices usually present a high insertion loss and low fabrication yield. To reduce the insertion loss and enhance the fabrication yield of FPW device, a 1.5 £gm-thick silicon-trench reflective grating structure (RGS), a high electromechanical coupling coefficient ZnO thin-film and a 5 £gm-thick silicon oxide membrane substrate are adopted in this research. The influences of the amount of silicon trench and the distance between inter-digital transducer (IDT) and RGS on the insertion loss and quality factor of FPW device are investigated. The main fabrication technology adopted in the study is bulk micromachining technology and the main fabrication steps include six thin-film deposition and five photolithography processes. Under the optimized conditions of the sputtering deposition processes (200¢J substrate temperature, 200 W radio-frequency power and 75% gas flow ratio), a high C-axis (002) orientation ZnO piezoelectric thin-film with 31.33% electromechanical coupling coefficient can be demonstrated. The peak of XRD intensity of the standard ZnO film occurs at diffraction angle 2£c = 34.422¢X, which matches well with our results (2£c = 34.282¢X). By controlling the thickness of ZnO/Au/Cr/SiO2/Si3N4 sensing membrane less than 6.5 £gm-thick, the fabrication yield of FPW device can be improved and a low operation frequency (6.286 MHz) and high mass sensitivity (-113.63 cm2 / g) can be achieved. In addition, as the implemented FPW device with four silicon trenches RGS and 37.5 £gm distance between IDT and RGS, a low insertion loss (-40.854 dB) and very high quality factor (Q=206) can be obtained. Keywords¡Gflexural plate-wave; silicon-trench reflective grating structure; electromechanical coupling coefficient; ZnO; bulk micromachining technology

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.