SAW RFID devices using connected IDTs as an alternative to conventional reflectors for harsh environments

International audienceRemote interrogation of surface acoustic wave ID-tags imposes a high signal amplitude which is related to a high coupling coefficient value (K 2) and low propagation losses (α). In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the conventional configuration, i.e. one interdigital transducer (IDT) and several reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the detected signal using direct transmission between IDTs instead of the reflection from passive reflectors. This concept can therefore increase the interrogation scope of ID-tags made on conventional substrate with high K 2 value. Moreover, it can also be extended to suitable substrates for harsh environments such as high temperature environments: the materials used exhibit limited performances (low K 2 value and relatively high propagation losses) and are therefore rarely used for identification applications. The concept was first tested and validated using the lithium niobate 128°Y-X cut substrate, which is commonly used in ID-tags. A good agreement between experimental and numerical results was obtained for the promising concept of connected IDTs. The interesting features of the structure were also validated using a langasite substrate, which is well-known to operate at very high temperatures. Performances of both substrates (lithium niobate and langasite) were tested with an in-situ RF characterization up to 600°C. Unexpected results regarding the resilience of devices based on congruent lithium niobate were obtained. Index Terms-high temperature, lithium niobate, radio frequency identification (RFID), surface acoustic wave (SAW

Dispositifs d'Affichage de Sensations Tactiles à Base de Microsystèmes Électro-Mécaniques (MEMS) Magnétiques : Conception, Réalisation et Tests

Tactile display devices are systems bound to provide a tactile feedback to their users. They improve human-machine interfaces in the fields of virtual or augmented reality. This report deals with the contribution of magnetically actuated micro-electro-mechanical systems (MEMS) to the elaboration of easily integrable tactile display devices.A state of the art of actuation techniques used in existing devices is proposed, along with a requirements analysis for tactile applications. Magnetostatic actuation was considered for these needs.First tactile display device prototypes are designed as a network of 4x4 hybrid elastomeric micro-actuators with a 2 mm pitch, and combined microfabrication and conventional fabrication techniques.The conception and elaboration of these micro-actuators is detailed. High vibration amplitudes can be reached using pulse actuation (up to 200 µm), with instantaneous forces of 32 mN per actuator. Sensitive tests were also achieved in order to confirm their efficiency.Micro-coils were also developed in order to fulfill the magnetic micro-actuators needs, and meet the requirements for tactile display devices. Various micro-coil configurations suitable for power actuation are proposed and elaborated by electrodeposition. Micro-actuators based on elastomeric membranes were fabricated and characterized. The contribution of these micro-coils for micro-actuation is discussed face with hybrid approachesLes dispositifs de stimulation tactile sont des systèmes destinés à fournir un retour sensoriel à leurs utilisateurs. Ils enrichissent les interfaces homme-machine dans les applications de réalité virtuelle ou augmentée. Ce mémoire traite de l’apport des microsystèmes électromécaniques (MEMS) actionnés magnétiquement à la réalisation d’interfaces de stimulation tactile facilement intégrables.Un état de l’art des solutions d’actionnement mises en œuvre dans les dispositifs existants est proposé, ainsi qu'une définition des besoins pour les applications visées. Les solutions retenues sont basées sur l’actionnement magnétostatique.Les premiers prototypes d’interfaces de stimulation tactile se présentent sous la forme d'un réseau de 4x4 actionneurs élastomériques hybrides avec un pas de 2 mm, combinant microfabrication et techniques de fabrication conventionnelles. La conception et l’élaboration de ces micro-actionneurs est présentée en détail. L'actionnement impulsionnel permet d'atteindre des amplitudes de vibration importantes (jusqu'à 200 µm) et des forces élevées (32mN par actionneur). Des tests sensoriels confirment enfin leur efficacité. Des micro-bobines ont aussi été développées afin de répondre aux besoins des micro-actionneurs magnétiques, ainsi qu'au cahier des charges des interfaces de stimulation tactile. Diverses configurations de micro-bobines adaptées à l'actionnement de puissance sont proposées et réalisées par électrodéposition. Des micro-actionneurs basés sur ces bobines intégrées ont alors été réalisés, puis caractérisés. L'utilité des bobines pour les micro-actionneurs de puissance est alors discutée face aux solutions d’actionnement hybrid

Tactile Display Devices Based on Magnetic Micro-Electro-Mechanical Systems (MEMS) : Conception, Elaboration and Characterization

Les dispositifs de stimulation tactile sont des systèmes destinés à fournir un retour sensoriel à leurs utilisateurs. Ils enrichissent les interfaces homme-machine dans les applications de réalité virtuelle ou augmentée. Ce mémoire traite de l’apport des microsystèmes électromécaniques (MEMS) actionnés magnétiquement à la réalisation d’interfaces de stimulation tactile facilement intégrables.Un état de l’art des solutions d’actionnement mises en œuvre dans les dispositifs existants est proposé, ainsi qu'une définition des besoins pour les applications visées. Les solutions retenues sont basées sur l’actionnement magnétostatique.Les premiers prototypes d’interfaces de stimulation tactile se présentent sous la forme d'un réseau de 4x4 actionneurs élastomériques hybrides avec un pas de 2 mm, combinant microfabrication et techniques de fabrication conventionnelles. La conception et l’élaboration de ces micro-actionneurs est présentée en détail. L'actionnement impulsionnel permet d'atteindre des amplitudes de vibration importantes (jusqu'à 200 µm) et des forces élevées (32mN par actionneur). Des tests sensoriels confirment enfin leur efficacité. Des micro-bobines ont aussi été développées afin de répondre aux besoins des micro-actionneurs magnétiques, ainsi qu'au cahier des charges des interfaces de stimulation tactile. Diverses configurations de micro-bobines adaptées à l'actionnement de puissance sont proposées et réalisées par électrodéposition. Des micro-actionneurs basés sur ces bobines intégrées ont alors été réalisés, puis caractérisés. L'utilité des bobines pour les micro-actionneurs de puissance est alors discutée face aux solutions d’actionnement hybrideTactile display devices are systems bound to provide a tactile feedback to their users. They improve human-machine interfaces in the fields of virtual or augmented reality. This report deals with the contribution of magnetically actuated micro-electro-mechanical systems (MEMS) to the elaboration of easily integrable tactile display devices.A state of the art of actuation techniques used in existing devices is proposed, along with a requirements analysis for tactile applications. Magnetostatic actuation was considered for these needs.First tactile display device prototypes are designed as a network of 4x4 hybrid elastomeric micro-actuators with a 2 mm pitch, and combined microfabrication and conventional fabrication techniques.The conception and elaboration of these micro-actuators is detailed. High vibration amplitudes can be reached using pulse actuation (up to 200 µm), with instantaneous forces of 32 mN per actuator. Sensitive tests were also achieved in order to confirm their efficiency.Micro-coils were also developed in order to fulfill the magnetic micro-actuators needs, and meet the requirements for tactile display devices. Various micro-coil configurations suitable for power actuation are proposed and elaborated by electrodeposition. Micro-actuators based on elastomeric membranes were fabricated and characterized. The contribution of these micro-coils for micro-actuation is discussed face with hybrid approache

Non-leaky longitudinal acoustic modes in ScxAl1-xN/sapphire structure for high-temperature sensor applications

International audienceMultilayered structures based on wide bandgap nitride piezoelectric thin films are very attractive for high-temperature surface acoustic waves (SAW) sensor applications. In this respect, scandium aluminium nitride (ScAlN) films are of particular interest as they combine enhanced piezoelectric properties and slower acoustic waves velocities when the Sc content steadily increases up to 40%. This property offers the possibility to combine slow ScAlN films on fast substrates like sapphire, to generate higher-order SAW modes which often show a better electromechanical coupling coefficient k 2 compared to zero-order modes. In this letter, we show that low-attenuated longitudinal SAW can be generated in ScxAl1-xN/Sapphire structure, for x parameter varying in a large range. This theoretical result is then confirmed by the experimental investigation of SAW resonators based on highly-textured (002) Sc0.09Al0.91N films sputtered on c-cut sapphire substrates. It is finally shown that the use of electrodes based on metals with high density can lead to SAW structures offering a unique combination between a large bandgap over 5 eV, a k 2 value beyond 1% and a high SAW velocity near 10000 m/s

First investigations on stoichiometric lithium niobate as piezoelectric substrate for high-temperature surface acoustic waves applications

International audienceSurface acoustic waves (SAW) technology is very promising to achieve high-temperature wireless sensors. However, there is currently a need for piezoelectric substrates with a high electromechanical coupling coefficient (K2 > 1%), able to operate under harsh environments, especially in the intermediate temperature range (300-600°C). None of the conventional SAW substrate can face this challenge. In particular congruent lithium niobate, whose K2 can exceed 5%, shows serious limitations from 300°C, mainly related to Li vacancies. Recent studies have demonstrated the potential of stoichiometric lithium niobate (s-LN) for high-temperature bulk acoustic waves applications. In this paper, we investigate this piezoelectric material for high-temperature SAW applications. In particular, we examine carefully the potential structural and chemical changes that s-LN surface can undergo during a high-temperature exposure. Finally, SAW resonators based on s-LN substrates are in situ characterized up to 600°C

Epitaxial Growth of Sc0.09Al0.91N and Sc0.18Al0.82N Thin Films on Sapphire Substrates by Magnetron Sputtering for Surface Acoustic Waves Applications

International audienceScandium aluminum nitride (ScxAl1-xN) films are currently intensively studied for surface acoustic waves (SAW) filters and sensors applications, because of the excellent trade-off they present between high SAW velocity, large piezoelectric properties and wide bandgap for the intermediate compositions with an Sc content between 10 and 20%. In this paper, the growth of Sc0.09Al0.91N and Sc0.18Al0.82N films on sapphire substrates by sputtering method is investigated. The plasma parameters were optimized, according to the film composition, in order to obtain highly-oriented films. X-ray diffraction rocking-curve measurements show a full width at half maximum below 1.5°. Moreover, high-resolution transmission electron microscopy investigations reveal the epitaxial nature of the growth. Electrical characterizations of the Sc0.09Al0.91N/sapphire-based SAW devices show three identified modes. Numerical investigations demonstrate that the intermediate compositions between 10 and 20% of scandium allow for the achievement of SAW devices with an electromechanical coupling coefficient up to 2%, provided the film is combined with electrodes constituted by a metal with a high density

Bandgap energy bowing parameter of strained and relaxed InGaN layers,

International audienceThis paper focuses on the determination of the bandgap energy bowing parameter of strained and relaxed InxGa1−xN layers. Samples are grown by metal organic vapor phase epitaxy on GaN template substrate for indium compositions in the range of 0<x<0.25. The bangap emission energy is characterized by cathodoluminescence and the indium composition as well as the strain state are deduced from high resolution X-ray diffraction measurements. The experimental variation of the bangap emission energy with indium content can be described by the standard quadratic equation, fitted using a relative least square method and qualified with a chi square test. Our approach leads to values of the bandgap energy bowing parameter equal to 2.87±0.20eV and 1.32±0.28eV for relaxed and strained layers (determined for the first time since the revision of the InN bandgap energy in 2002), respectively. The corresponding modified Vegard’s laws describe accurately the indium content dependence of the bandgap emission energy in InGaN alloy and for the whole range of indium content. Finally, as an example of application, 3D mapping of indium content in a thick InGaN layer is deduced from bandgap energy measurements using cathodoluminescence and a corresponding hyperspectral map