This paper presents the fabrication and characterization of a biaxial MEMS (MicroElectroMechanical System) scanner based on PZT (Lead Zirconate Titanate) which incorporates a low-absorption dielectric multilayer coating, i.e., a Bragg reflector. These 2 mm square MEMS mirrors, developed on 8-inch silicon wafers using VLSI (Very Large Scale Integration) technology are intended for long-range (>100 m) LIDAR (LIght Detection And Ranging) applications using a 2 W (average power) pulsed laser at 1550 nm. For this laser power, the use of a standard metal reflector leads to damaging overheating. To solve this problem, we have developed and optimised a physical sputtering (PVD) Bragg reflector deposition process compatible with our sol-gel piezoelectric motor. Experimental absorption measurements, performed at 1550 nm and show up to 24 times lower incident power absorption than the best metallic reflective coating (Au). Furthermore, we validated that the characteristics of the PZT, as well as the performance of the Bragg mirrors in terms of optical scanning angles, were identical to those of the Au reflector. These results open up the possibility of increasing the laser power beyond 2W for LIDAR applications or other applications requiring high optical power. Finally, a packaged 2D scanner was integrated into a LIDAR system and three-dimensional point cloud images were obtained, demonstrating the scanning stability and operability of these 2D MEMS mirrors.

The paper presents a miniaturized pitch/roll gyroscope with the lowest angle random walk (ARW of 600 mu dps/root Hz) and lowest bias instability (BI of 2.8 dph) ever recorded on planar MEMS sensors for in-plane rate capture. The device is based on NEMS resistive sensing, features a 1.2 mm(2) footprint, a 100-Hz bandwidth, and can be combined to yaw gyroscopes for ultra-low-noise 3-axis systems. The key advancement over previous implementations is represented by a 10-fold increase in the scale factor, obtained through a novel architecture which, combined with quadrature compensation, optimizes at the same time the energy transfer to the NEMS gauges and the robustness to vibrations.

The paper discusses the design and performance of mode-split MEMS gyroscopes, based on NEMS piezoresistive detection, as a function of the frequency of the operating modes. The key concept is the independence of the performance (in terms of footprint, sensitivity and noise) with respect to the working frequency, which allows the design of more robust devices against external vibrations. A yaw gyroscope with modes around 50 kHz and a 1.5-mm 2 footprint is fabricated, coupled to the same driving/sensing electronics and comparatively tested against a 20-kHz twin device: the sensor shows a scale factor of 1.4 mV/dps, noise in the mdps/Hz 1/2 range and 0.5°/h stability, validating the theoretical considerations.

Downsizing and compatibility with MEMS silicon foundries is an attractive path towards a large diffusion of photoacoustic trace gas sensors. As the photoacoustic signal scales inversely with the chamber volume, a trend to miniaturization has been followed by several teams. We review in this article the approach initiated several years ago in our laboratory. Three generations of components, namely a 40 mm 3 3D-printed cell, a 3.7 mm 3 silicon cell, and a 2.3 mm 3 silicon cell with a built-in piezoresistive pressure sensor, have been designed. The models used take into account the viscous and thermal losses, which cannot be neglected for such small-sized resonators. The components have been fabricated either by additive manufacturing or microfabrication and characterized. Based on a compilation of experimental data, a similar sub-ppm limit of detection is demonstrated. All three versions of photoacoustic cells have their own domain of operation as each one has benefits and drawbacks, regarding fabrication, implementation, and ease of use.

Photoacoustic (PA) spectroscopy is one of the most sensitive technique used to monitor chemical emission or detect gas traces. Coupled to quantum cascade lasers, this system is widely used in a large number of application fields from industrial control to health monitoring. Mass production for a large dissemination of such systems requires however further development for both decreasing their footprint and manufacturing cost. Since the last 6 years CEA-LETI has developed different versions of miniaturized photoacoustic cells. We have already demonstrated the detection of gas traces with a tiny silicon based-PA cell. Nevertheless, this first result was obtained with commercial MEMS microphones. Even if these components are reliable and enough performant they are not dedicated to photoacoustic gas detection and cannot be easily integrated into a fabrication process flow. To cope with these issues we suggest using both the M&NEMS technology and the MIR photonics. The new PAdetector termed microPA is built by stacking two 200 mm wafers: a sensor wafer, which includes the microphone (MEMS mechanical diaphragm and NEMS piezoresistive gauges), capillaries and fluidic ports, and a cap wafer, which includes the PA cell, the expansion volume, SiGe waveguides guiding the light into the PA cell, metal routing and electric contacts. Frequency response measurements as well as PA gas detection have been carried out. The system shows a mechanical resonance of the diaphragm at the frequency of 6500 Hz, in good agreement with the simulation. First CO2 and CH4 tests in laboratory condition demonstrates a limit of detection in the ppm range and a NNEA of 10-8 W.cm-1.Hz-1/2.

This paper reports the conception, the fabrication and the electrical testing of an overdamped silicon accelerometer dedicated to vibrating environments. Squeeze-film damping effects are implemented to drastically reduce the mechanical component bandwidth while keeping a satisfactory resolution. Mechanical filtering of vibrations above 3 Hz is expected to strongly lower the mechanical overcharge and the fatigue of the structure that may occur when the MEMS is exposed to large parasitic vibrations and shocks. Such a low-pass system has not been reported yet, to the best of our knowledge.

This paper is concerned with the optimization of an active vibration micro-isolator. The process is applied to the whole system including the passive structure, the piezoelectric transducers, the electrical interfaces and the controller. An efficient optimization algorithm based on an interval computation method is used. The authors' general objective is to include and develop an early optimization step in the systemic design process of a smart structure. For this purpose, an analytic mathematical model is built, which describes the analytic equations of motion of the main controlled natural mode shape of the micro-isolator. Basically, the method is applicable to a large scale of systems if an analytic description is developed. As case study, the controller and the passive structure are simultaneously optimized so as to obtain a compromise between transmissibility, control energy level and beam strength. The first results obtained are relevant.

A piezoelectric micro active suspension device has been developed for the application of active isolation of sensitive electronic devices such as frequency generators or inertial sensors. The developed strategy is based on a classical skyhook active damper but adapted and optimised to allow robust implementation onto an adaptive microelectromechanical systems (MEMS). The micro suspension is a silicon beam structure etched in a silicon on insulator (SOI) wafer and is equipped with a pair of piezoelectric transducers obtained from a lead zirconate titanante thin film sandwiched between pairs of electrodes. High performance transducers allow application of the active isolation strategy and demonstrate the possibility to implement skyhook damping with low-voltage control level.

Thin PZT films have a major interest for active control of mechanical structures. Precisely, it is an open field for the isolation of micro-components sensitive to dynamic effects. Indeed, the electronic components used, for example, in aircraft endure intense vibrations due to acceleration. These vibrations have some disturbing effects on the frequency stability and on the usable life of the electronic elements. The isolation of these elements becomes crucial to protect them from the vibrating environment. In order to manage this problem, it is advisable to isolate the electronic card either at the case level or at the card level or at the sensitive element level. The latter solution was chosen. Thus, we have direct access to the control electronics and the energy sources and the control energy is lower. An active suspension system is developed between the support and the sensitive element to be isolated. An original active suspension system is designed. Some modeling difficulties arise due to the existence of the inevitable bottom electrode common to the actuating layers and to the sensing layer.

An original approach of the active vibration control of rotor systems supported by Active Magnetic Bearing (AMB) is introduced. This control is intended to stabilize flexible rotor with strong gyroscopic effect without a model of the structure. The magnetic bearing is used alternatively as a sensor and an actuator. So, a pair of AMB corresponds to a sensor and an actuator ideally collocated. In literature, it is proven that this configuration guarantees the asymptotic stability of the closed-loop system. Therefore, the model of the rotor is not necessary to tune the controller. The numerical results are indicating high possibility of reducing the vibrations of the rotating machines supported by magnetic bearings without instabilities.

Electronic components bonded on a moving structure endure some intense dynamical solicitations due to rigid body movements and vibrations of the structure at fixation points. Vibrations have some disturbing effects on the frequential stability and the use-life of sensitive components. Consequently, it becomes crucial to protect them from the vibrating environment. The MEMS device we propose is a micro active suspension. It can be hybridized directly on electronic cards to isolate sensitive components in situ. So energy necessary for active control can be provided by a surrounding electronic source. We expect a low consumption level because of the small weight of components to isolate. The needed actuators and sensors are included in the micro suspension from a piezoelectric layer (PZT) spread on a common reference electrode. We made an experimental setup to validate the active functions. The results we have obtained show anomalies when we use simultaneously actuators and sensors. We suspect that electrical coupling between the transducers occurs through the common reference electrode. A complete model has been developed by adding to a mechanical model the Kirchhoff's current law occuring at reference electrode level. The computed results are quite similar to experimental ones.