Resonant micro-electromechanical system (MEMS) beam accelerometers have demonstrated remarkable sensitivity and stability, enabling applications in seismology and gravimetry while keeping a small footprint. However, mechanical crosstalk and resonance mode coupling have shown to be specially detrimental to the operation of this kind of accelerometers, especially when employing nanoresonators as the transduction element. In this study, we investigate the mechanical crosstalk of nanoresonator-based accelerometers, through measurement, modeling, and simulation of a pendulum accelerometer. We introduce a novel methodology for the early identification of crosstalk during the accelerometer design phase, facilitating proactive detection and mitigation of this issue. Finally, we propose an innovative technique that effectively minimizes mechanical crosstalk with a minimum impact on performance, applicable to a large number of structures. This involves the mechanical decoupling of vibrational modes within the beam resonator from the rest of the accelerometer structure.

This work presents a novel single-axis gyroscope for pitch (or roll) rate detection based on an improved stress amplification architecture for the piezoresistive nanogauges of the sense mode. The design decouples the lever tilting angle, responsible of the stress applied onto the gauges, and thus of the scale-factor, from the proof mass tilting angle induced by the Coriolis force: this determines a sensitivity increase and thus the possibility to obtain high-performance pitch rate detection. The sensor is coupled to an integrated circuit which sustains the drive oscillation and reads out the open-loop sense chain. Results show 306 mu dps/vHz angle random walk and 0.12 degrees/hr bias stability, which rank this device among the top performing pitch/roll gyroscopes in the literature, in ultra-small footprint.

The paper researches on the origin of scale-factor (SF) and zero-rate-offset (ZRO) drift in gyroscopes based on NEMS resistive sensing, towards effective calibration and compensation for further performance improvement. It is shown that the SF drift is affected by the mode-split behaviour in temperature, induced by differences in the temperature coefficient of frequency (TCf) of the two modes, and further perturbed by softening/hardening in operation. Measuring the mode-split with 10-mHz accuracy enables to understand the behaviour and adjust the drive motion to reduce the mode-split drift by a factor 100. At the same time, it is shown how temperature tracking via the drive-mode resonance, and following output compensation, brings down stability to values below 0.01 °/hr.

This paper presents the simulation results of a piezoelectric MEMS loudspeaker. The micro-fabricated device is composed of two wafers, the first one features two bending piezoelectric actuators with large displacements, and the second one features a mobile rigid plate surrounded by a small interstice providing a thermoviscous layer hence avoiding an acoustic short circuit between its front and back sides. Performances of the loudspeaker are evaluated using a lumped element model and a finite element model to estimate the pressure generated by the loudspeaker in free field and in an ear-occluded coupler. Size variants of the design and their models are presented. The current design allows a radiated pressure of 80 dBSPL from 500 Hz at 10 cm and at 30 V-pp for a 64 mm(2) footprint in free field, and more than 130 dBSPL in a IEC 60318-4 coupler with the same actuation voltage, which is above the known performances of the state of the art for MEMS loudspeakers with such dimensions.

Resonant-beam accelerometers based on nanoresonators have demonstrated that reducing the size of the sensing element allows overcoming the sensitivity-bandwidth trade-off [1]. Here we report on an improvement of the performance of such sensors, through an enhancement of the wafer-level packaging (WLP). We perform a study of the different noise sources present in the system, and we show that an improvement of the vacuum level allows overcoming the thermomechanical noise of the proof mass which – so far – limited the previous generation of sensors.

This paper presents the simulation results of a piezoelectric MEMS loudspeaker. The micro-fabricated device is composed of two wafers, the first one featuring two bending piezoelectric actuators with large displacements, and the other one featuring a mobile rigid plate surrounded by a small interstice providing a thermoviscous layer hence avoiding an acoustic short-cut between its front and back sides. The current design allows a radiated pressure of 80 dBSPL from 1 kHz at 10 cm and at 30 Volts for a 64 mm2 footprint, which is above the known performances of the state of the art for MEMS loudspeakers with such dimensions.

We present an optical transduction method adapted to the detection of low frequency thermal perturbations and implemented for photothermal trace gas detection. The transducer is a π -phase shifted fiber Bragg grating, stabilized and interrogated by the Pound-Drever-Hall method. The principle of detection is based on the frequency shift of the narrow optical resonance, induced by the temperature variations. In temperature measurement mode, the stabilization leads to an estimated limit of detection of 1 µK at room temperature and at a frequency of 40 Hz. When the fiber transducer is placed in a gas cell, CO 2 is detected by photothermal spectroscopy with a limit of detection of 3 ppm/ H z . This novel method, based on a single fiber, offers robustness, stabilized operation and remote detection capability.

We present the design, fabrication and characterization of a resonant accelerometer combining piezoresistive nanoresonators with a micrometric proof mass, achieving at the same time an exceptional frequency sensitivity (up to 10%/g) and a large bandwidth (1.5 kHz) with respect to conventional technologies. These sensors are fabricated with a 200 mm MEMS technology.

This paper demonstrates, for the first time, an on-chip integration of a photoacoustic (PA) detector, one of the main building blocks required for chemical sensing. This MEMS PA detector consists of a miniaturized PA cell within an acoustic transducer based on an innovative microphone architecture. Coupled with a quantum cascade laser (QCL) source, this trace gas detector can measure very low concentrations of less than one part per million.

For the first time, functional in-plane deflection microphones have been fabricated, validating a new concept based on a diaphragm moving in the plane of the substrate and inducing strain on piezoresistive Si nano-gauges. Such architecture, integrating furthermore a back cavity, leads to microphones with a smaller footprint that preserve at the same time high performance, and is therefore adapted for the achievement of miniature sensors and their integration for medical applications or consumer electronics.

This article presents the modeling of a MEMS microphone with an original architecture formed of mechanical structures moving in the plane of the substrate. On the contrary of most microphones generally constituted of an oscillating membrane, some transducers developed by the CEA-LETI with M&NEMS technology use micro beams moving in the plane of the silicon wafer under the effect of an acoustical wave. These micro-structures are connected to the substrate by flexible micro-hinge and strain silicon nano-gauge producing a variation in resistance by piezoresistive effect. After the description of the design and functioning of the microphone under study, the vibroacoustic model of the fluid-structure coupling is presented. Considering the dimensions of the MEMS transducer close to the thermal and viscous boundary layers thicknesses, this model has to include diffusion phenomena. The model is discretized using the finite element method and the weak formulation is implemented using COMSOL Multiphysics (R) software. The pressure sensitivity of the microphone is calculated and compared with an analytical lumped model to asses the numerical model. Pressure and velocity fileds are also computed. Solutions of simulations are interpreted by focusing on phenomena influencing the sensitivity of this novel sensor design. In particular, the influence of the geometry and the role of the different part of the transducer (back cavity, mechanical structures) are studied.

This paper investigates the resilience to mechanical vibration of tuning fork MEMS gyroscopes and presents the limitations of this device. We focus our study on mechanical vibrations near the first three resonance frequencies corresponding to the in-phase and anti-phase drive modes and the sense mode. This original work quantifies the rejection capability of the anti-phase mode to external vibrations in comparison to the in-phase mode resulting in a ratio of 390. In-phase frequency mechanical vibrations can result in mechanical non-linearities visible in the gyroscope response. This paper demonstrates also the strong impact of the in-phase mode on the gyroscope operation leading to failure when it is excited simultaneously with the anti-phase mode. This issue is common to tuning fork gyroscopes and only phase mode control or shift to higher frequencies can preserve normal gyroscope operation at the bandwidth 0 – 50 kHz.

Electret microphones dedicated to consumer electronics (mobile phone) and medical applications (hearing aids) have reached the miniaturization limits. Since the release of the first microphone based on silicon micromachining, electret microphones are constantly replaced by MEMS microphones. However, reduction of the diaphragm surface for MEMS is a fundamental limit to the miniaturization of microphones. The following paper present a novel MEMS microphone architecture that is developed in the frame of the ANR MADNEMS project. It uses micro beams that deflect in the plane of the base wafer. Signal transduction is achieved by piezoresistive nanogauges integrated in the microsystem and attached to the micro beams. Acoustic pressure fluctuations lead to the deflection of the micro beams which produces a stress concentration in the nano gauges. Such architecture enables us to reduce the surface of the deflecting element and leads to a microphone with a smaller footprint that preserves at the same time high performances. Accurate simulations based on the Finite Element Method of the discussed transducer couple acoustic, mechanical and electric behavior of the system. A 3D model of the microsystem would be too expensive in terms of computation time and memory with a poor mesh quality. This type of model is not suitable for the design of the MEMS microphone where numerous geometry parameters have to be revised. That is why a major effort has been devoted to modeling the microsystem by a 2D model. In particular, as the system is not symmetrical due to the deflection of the beams, a mechanical equivalent 2D model was proposed. This paper presents the modeling approach used to taken into account mechanical and thermal boundary condition at the walls, and the phenomena of viscous and thermal diffusion involved in the air. Its implementation in a finite element code allows the numerical calculation of the pressure sensitivity of the microphone. The numerical results were validated by an analytical model. The highlighting of the main physical phenomena in the microsystem, allowed to develop simplified models (Lumped Elements and Low Reduced Frequency) more suitable to the design of MEMS.

Electret microphones dedicated to consumer electronics and medical applications (hearing aids) have reached the miniaturization limits. Since the release of the first microphone based on silicon micromachining, electret microphones are constantly replaced by MEMS microphones. Regardless of the transduction principle (capacitive, piezoresistive, piezoelectric, optical), all of the MEMS microphones reported in the state of the art literature are based on a membrane deflecting out of the plane of the base wafer. On the contrary, the novel microphone architecture that is developed in the frame of the ANR MADNEMS project uses micro beams that deflect in the plane of the base wafer. The presented microphone profits of the well known technological platform developed at CEA LETI that integrates micro and nanofabrication to deliver high- performance MEMS sensors. Transduction is achieved by piezoresistive nano gauges integrated in the microsystem, arranged in a Wheatstone bridge and attached to micro beams. Acoustic pressure fluctuations lead to the deflection of the micro beams which produces a stress concentration in the nano gauges. Such architecture enables us to reduce the surface of the deflecting element and leads to a microphone with a smaller footprint that preserves at the same time high performance. Accurate simulations of the discussed transducer couple acoustic, mechanic and electric behavior of the system. Due to micrometric dimensions of acoustic vents, thermal and viscous boundary layers have to be taken into account. Additionally the influence of backspace volume on pressure response has to be examined. The paper will initially present general principle of operation and the technological process; then, the coupled microphone model will be briefly presented. Finally we will focus on the parametric tests (technological process properties) and electromechanical test (mechanical properties of MEMS) of the microphones.

La plateforme technologique M&NEMS developpee au CEA-LETI permet d'integrer des nano fils de Silicium employes comme jauges de contraintes en exploitant l'effet piezoresistif. Ce principe de detection est adapte pour la realisation de senseurs auditifs miniaturises destines a des applications dans le domaine medical ou l'electronique grand public. Le microphone MEMS etudie possede une architecture originale qui fait intervenir des structures mecaniques sensibles oscillant dans le plan du dispositif. Apres la description du principe de fonctionnement, cet article presente la demarche de modelisation employee pour la prise en compte des conditions aux limites mecaniques et thermiques, et des phenomenes de diffusion visqueuses et thermiques dans l'air (couches limites). Son implantation dans un code elements finis permet le calcul numerique de la sensibilite en pression du microphone. Les solutions des simulations sont interpretees en se focalisant sur les phenomenes influant sur la sensibilite de cette nouvelle architecture de capteur.

The miniaturization of microphones is of great interest for several fields, such as medical applications (audio implants), or consumer electronics (cell phones). Almost all existing miniature microphones rely on electrostatic transduction and offer good performances (sensitivity, frequency bandwidth). However, their sensitivity, proportional to the membranes area, would be dramatically reduced in case of extreme miniaturization. A new concept of microphones developed by CEA-LETI, which uses membranes moving in the plane of the substrate and inducing strain on piezoresistive Si nano-gauges (M&NEMS technology), seems promising for its miniaturization potential without significant decrease of sensitivity. The design and optimization of such planar piezo-resistive microphone require a deep understanding of its acoustic and vibroacoustic behavior. Regarding the small dimensions of the slits (1–100µm) and the sharp discontinuities in the microphones structure, viscous and thermal effects in the boundary layers and turbulent perturbations are of great importance, and must then be taken into account with high accuracy in device modeling. The aim of the present work is to provide accurate analytical and numerical (FEM) models able to gather all these effects in a consistent manner, and to suggest an experimental method to check their validity.