The goal of this paper is to determine the bulk acoustic wave (BAW) propagation velocities (quasi-longitudinal, quasi-shear vertical and quasi-shear horizontal) in two important piezoelectric smart materials, Lithium Niobate (LiNbO3) and Lithium Tantalate (LiTaO3). To determine the BAWpropagation velocities, the BAWelemental equations are deduced. The BAWvelocities are calculated for each direction by solving the Christoffel's equation systematically based on the theory of acoustic waves in anisotropic solids exhibiting piezoelectricity. The modification of the BAW velocities by the piezoelectric effect are calculated and graphically compared with the velocities in the corresponding non-piezoelectric materials. Furthermore, the electromechanical coupling factors are defined and investigated. The results obtained in this study can be applied to signal processing, sound systems and wireless communication in addition to the improvement of surface acoustic wave (SAW) devices and military defense equipment.
Since a few decades, frequency control technology has been at the heart of modern day electronics due to its huge areaof applications in communication systems, computers, navigation systems or military defense. Frequency controldevices provide high frequency stabilities and spectral purities in the short term domain. However, improvement of theperformance of these devices, in terms of frequency stability, remains a big challenge for researchers. Reducing noise inorder to increase the short term stability and avoid unwanted switching between channels is thus very desirable. It iscommonly admitted that the fundamental limitation to this short-term stability is due to flicker frequency noise in theresonators. In this manuscript, a first chapter recalls some basic facts about acoustic, crystallography and definitions oftime and frequency domain needed to explore ultra-stable resonators and oscillators. The second chapter is devoted to asummary of the literature on flicker frequency noise. Then, the third chapter concerns our studies on Handel's quantum1/f noise model, which although criticized by many, is still the only one that provides an estimation of the flooramplitude of 1/f noise that is not invalidated by experimental data. In the fourth chapter, another approach, based on thefluctuation-dissipation theorem, is used in order to put numerical constraints on a model of 1/f noise caused by aninternal (or structural) dissipation proportional to the amplitude and not to the speed. The last chapter is devoted toexperimental results. An ultra-stable resonator used during this study is described. Phase noise measurements on severalbatches of resonators are given. Measurements of resonator parameters have been done at low temperature in order tocorrelate them with noise results. Another approach with a procedure that use transient pseudo periodic oscillations andput to their limits the capacities of presently available digital oscilloscopes, is presented, in order to assess rapidly thequality of various resonators. ...
Since a few decades, frequency control technology has been at the heart of modern day electronics due to its huge areaof applications in communication systems, computers, navigation systems or military defense. Frequency controldevices provide high frequency stabilities and spectral purities in the short term domain. However, improvement of theperformance of these devices, in terms of frequency stability, remains a big challenge for researchers. Reducing noise inorder to increase the short term stability and avoid unwanted switching between channels is thus very desirable. It iscommonly admitted that the fundamental limitation to this short-term stability is due to flicker frequency noise in theresonators. In this manuscript, a first chapter recalls some basic facts about acoustic, crystallography and definitions oftime and frequency domain needed to explore ultra-stable resonators and oscillators. The second chapter is devoted to asummary of the literature on flicker frequency noise. Then, the third chapter concerns our studies on Handel's quantum1/f noise model, which although criticized by many, is still the only one that provides an estimation of the flooramplitude of 1/f noise that is not invalidated by experimental data. In the fourth chapter, another approach, based on thefluctuation-dissipation theorem, is used in order to put numerical constraints on a model of 1/f noise caused by aninternal (or structural) dissipation proportional to the amplitude and not to the speed. The last chapter is devoted toexperimental results. An ultra-stable resonator used during this study is described. Phase noise measurements on severalbatches of resonators are given. Measurements of resonator parameters have been done at low temperature in order tocorrelate them with noise results. Another approach with a procedure that use transient pseudo periodic oscillations andput to their limits the capacities of presently available digital oscilloscopes, is presented, in order to assess rapidly thequality of various resonators. Finally, conclusions and perspectives are given. ; Depuis quelques décennies, la technologie de contrôle de la fréquence a été au coeur de l'électronique des tempsmodernes grâce à son vaste domaine d'applications dans les systèmes de communication, les ordinateurs, les systèmesde navigation ou de défense militaire. Les dispositifs temps-fréquence fournissent des stabilités de fréquence et despuretés spectrales élevées dans le domaine de la stabilité court-terme. L'amélioration de la performance de cesdispositifs reste un grand défi pour les chercheurs. La réduction du bruit afin d'augmenter cette stabilité court-terme etd'éviter les commutations non souhaitées entre les canaux est donc très souhaitable. Il est communément admis que lalimitation fondamentale à cette stabilité court-terme est due au bruit flicker de fréquence des résonateurs. Dans cemanuscrit, un premier chapitre rappelle quelques faits de base sur l'acoustique, la cristallographie et les définitions dudomaine temps-fréquence nécessaires à l'étude des résonateurs et oscillateurs ultra-stables. Le deuxième chapitre estconsacré à un résumé de la littérature sur le bruit de fréquence en 1/f. Ensuite, le troisième chapitre concerne nos étudessur le modèle quantique de bruit en 1/f du Pr. Handel, qui, bien que critiqué par beaucoup, est encore le seul qui fournitune estimation de l'amplitude de plancher de bruit en 1/f et qui n'est pas infirmé par les données expérimentales. Dans lequatrième chapitre, une autre approche, basée sur le théorème de fluctuation-dissipation, est utilisée afin de mettre descontraintes numériques sur un modèle de bruit en 1/f causé par une dissipation interne (ou de structure) proportionnelleà l'amplitude, et non à la vitesse. Le dernier chapitre est consacré aux résultats expérimentaux. Le design et lesparamètres du résonateur ultra-stable utilisé lors de cette étude sont décrits. Les mesures de bruit de phase sur plusieurslots de résonateurs sont données. Les mesures des paramètres de résonateur ont été effectuées à basse température afinde les corréler avec les résultats de bruit. Afin d'évaluer rapidement la qualité des différents résonateurs, une autreapproche dans le domaine temporel a été testée. Elle utilise des oscillations pseudo-périodiques transitoires mettant lesoscilloscopes numériques actuellement disponibles à leurs limites de capacité. Enfin, les conclusions et perspectivessont présentées.
Microactuation of free standing objects in fluids is currently dominated by the rotary propeller, giving rise to a range of potential applications in the military, aeronautic and biomedical fields. Previously, surface acoustic waves (SAWs) have been shown to be of increasing interest in the field of microfluidics, where the refraction of a SAW into a drop of fluid creates a convective flow, a phenomenon generally known as SAW streaming. We now show how SAWs, generated at microelectronic devices, can be used as an efficient method of propulsion actuated by localised fluid streaming. The direction of the force arising from such streaming is optimal when the devices are maintained at the Rayleigh angle. The technique provides propulsion without any moving parts, and, due to the inherent design of the SAW transducer, enables simple control of the direction of travel.
[EN] The propagation of intense acoustic waves in a periodic medium (sonic crystal) is numerically studied. The medium consists in a structured fluid, formed by a periodic array of fluid layers with alternating linear acoustic properties and quadratic nonlinearity coefficient. The spacing between layers is of the order of the wavelength; therefore Bragg effects such as band gaps appear. We show that the interplay between strong dispersion and nonlinearity influences wave propagation. The classical waveform distortion process typical of intense acoustic waves in homogeneous media can be strongly altered when nonlinearly generated harmonics lie inside or close to band gaps. ; The work was supported by Spanish Ministry of Economy and Innovation and European Union FEDER through projects FIS2011-29731-C02-02 and MTM2012-36740-c02-02. A. Mehrem acknowledges Generalitat Valenciana the support from Santiago Grisolia program (grant 2012/029). ; Jimenez, N.; Sánchez Morcillo, VJ.; Mehrem Issa Mohamed Mehrem, A.; Hamham, EM.; Picó Vila, R.; García-Raffi, LM. (2015). Propagation of intense acoustic waves in sonic crystals. Physics Procedia. 70:271-274. https://doi.org/10.1016/j.phpro.2015.08.152 ; S ; 271 ; 274 ; 70
International audience ; High quality resonators for spatial and military applications are only made by unitary way and high speed directional etching of piezoelectric material is yet insufficiently developed to produce high aspect ratio microstructures. So, in this paper, we report on the theoretical definition and on the realization of BAW resonators, working at 20 and 40 MHz. Part of mechanical process is made by deep Reactive Ion Etching of AT- and SC-cut quartz crystal wafers. To avoid edge effects such as mechanical stresses induced by mounting structure or leakage of the vibration mode, we have to realize a good energy trapping of the selected resonant frequency. Several trapping methods can be used depending on the frequency, thereby changing the resonator design, such as mass loading by electrodes themselves, mesa forms (i.e. 1 to 3 mu m circular or elliptical steps), or radius of curvature on one face of the resonator at least. Here, for question of manufacturing, we choose to trap the energy by a mesa form. Fabrication of complete mesa architecture with bridges aperture (like in a bva structure) requires combining high depth (about 140 mu m for a 40 MHz 3(rd) overtone resonator), high aspect ratios, good uniformity over the entire wafer (for about 40 resonators), vertical wall profiles and reasonable etching selectivity. After describing different RIE processes, we analyze the quality of the realization through the surface roughness, the geometry, the homogeneity of the mesa-step, the wall profile.
International audience ; High quality resonators for spatial and military applications are only made by unitary way and high speed directional etching of piezoelectric material is yet insufficiently developed to produce high aspect ratio microstructures. So, in this paper, we report on the theoretical definition and on the realization of BAW resonators, working at 20 and 40 MHz. Part of mechanical process is made by deep Reactive Ion Etching of AT- and SC-cut quartz crystal wafers. To avoid edge effects such as mechanical stresses induced by mounting structure or leakage of the vibration mode, we have to realize a good energy trapping of the selected resonant frequency. Several trapping methods can be used depending on the frequency, thereby changing the resonator design, such as mass loading by electrodes themselves, mesa forms (i.e. 1 to 3 mu m circular or elliptical steps), or radius of curvature on one face of the resonator at least. Here, for question of manufacturing, we choose to trap the energy by a mesa form. Fabrication of complete mesa architecture with bridges aperture (like in a bva structure) requires combining high depth (about 140 mu m for a 40 MHz 3(rd) overtone resonator), high aspect ratios, good uniformity over the entire wafer (for about 40 resonators), vertical wall profiles and reasonable etching selectivity. After describing different RIE processes, we analyze the quality of the realization through the surface roughness, the geometry, the homogeneity of the mesa-step, the wall profile.
Electro-acoustic devices such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices have been in commercial use for over 60 years and can be found in applications ranging from specialised scientific and military equipment to consumer products, such as mobile telephones, TV and radio receivers, etc. Today by far the largest market for electro-acoustic devices is the telecommunication industry which annually consumes approximately three billion acoustic wave filters for frequency control alone. The development of new materials and technologies for electro-acoustic devices has gained a substantial and growing interest from both academic and industrial research communities in recent years due to the enormous growth in the telecommunication industry and other forms of wireless data communication. One of the bigger issues has been to replace the single crystalline substrates with thin film piezoelectric materials deposited by reactive sputtering. This would not only reduce the manufacturing costs but will also enable high frequency of operation and a wider choice of substrate materials. However, in order to obtain the material properties required for the intended application a detailed theoretical description of the reactive sputtering process is necessary since the texture and other functional properties of the piezoelectric material are extremely sensitive to the process parameters in addition to the structure of the underlying material. This thesis studies the reactive sputtering process and its application for the fabrication of thin film electro-acoustic devices. The aim has been to gain a further insight into the process and make use of this knowledge to improve the fabrication of electro-acoustic devices. In this work modelling of the reactive sputtering process has been improved by studying certain fundamental aspects of the process and in particular the dynamics of the processes taking place during sputtering both at the target and the substrate surfaces. Consequently, highly textured thin piezoelectric aluminium nitride films have been synthesized and thin film bulk acoustic resonators (FBAR) operating in the GHz range have been fabricated and studied.
