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.

This paper presents the development of a stress optic modulator which can be implemented in an optical sensor system such as LIDAR. In LIDAR, an Optical Phased Array (OPA), consisting of several optical waveguides, can be used to steer the direction of light beams. The beam steering can be achieved using phase shifters where the delay for different optical waveguides is changed via the waveguide optical index by applying a mechanical stress using thin-film piezoelectric actuators. Finite Element Method (FEM) simulation was used to design the stress optic modulator and demonstrators were built on 200 mm silicon wafers and thin-film Pb(Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> ,Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PZT) material. Electrical and optical measurements were performed on our stress optic modulator and show the efficiency of the PZT phase shifter as being in the range of VπLπ = 20-26 V.cm, with an estimated energy dissipation of 800 nW per π phase shift. The proposed method suggests an alternative path to low power and high frequency solid-state LIDAR optical sensor systems.

This paper presents a resonant asymmetric micro-mirror actuated using an Electro Active Polymer piezoelectric material. This element is a key component to develop optical sensor systems such as LIDAR. The working principle and the design of the micro-mirror is first presented. Then the technological realization is summarized. Finally electrical and electromechanical characterizations prove the functionality of the device. In particular, we measured the focused torsion mode at 9.054 kHz, in good agreement with the theoretical frequency. The mirror displacement is about 11 μm under only 30 Vrms, leading to a mechanical angle of ±2.5°. It opens the way of low cost and low temperature process to build Micro Electro Mechanical Systems for optical sensor applications.

In this paper we present the development of a resonant asymmetric micro mirror. In particular, we prove the possibility of using an Electro Active Polymer as actuation material. The working principle of the micro mirror and the design retained is first presented. Then the technological realization is summarized. We obtain micro mirror demonstrators and the first characterization results are given. These first promising results open the way of low cost and low temperature process actuators for Micro Electro Mechanical Systems.

Numerous applications require tactile interfaces today. In particular, many customers’ applications such as automotive, Smartphone, tablet PC or touch pad can be concerned by high performances, low voltage haptic interfaces which allow the user to interact with its environment by the sense of touch. This technology is already used but with limitations such as high power consumption and limited feedback effect because today a simple vibration is commonly obtained. We chose to work on the squeeze-film effect. It consists in changing the friction between the finger and a plate resonator. It provides high granularity level of haptic sensation. This paper deals with the design, realization and characterization of high performances actuators in order to promote the squeeze-film effect on a 4-inch transparent plate (diagonal of the plate). Using Finite Element Method (FEM) models, we select the best design, able to generate the highest plate displacement amplitude as possible. We built demonstrators using a generic technology based on thin-film Aluminum Nitride (AlN) actuators on glass substrate. Electromechanical characterizations prove that it is possible to obtain the focused substrate vibration amplitude using only 35V in amplitude. The integration of the thin-film actuator plate in a haptic demonstrator is now ongoing.

A Digital Loudspeaker Array (DLA) is an electro-mechanical transductor which receives a numerical signal as input data and allows the analogical conversion directly in the air. We designed PZT actuated membranes in order to obtain the highest acoustic pressure as possible. We built 256-MEMS-membranes DLAs using a generic PZT technology and digital acoustic reconstructions of the sound have been already demonstrated using our MEMS-DLA. In this paper, using FEM simulations, we evidence that residual stresses are responsible of the high distortion level measured on our demonstrators. A stress compensated technology was established using FEM approach. Acoustic characterization of stress compensated demonstrators proves distortion decreased and validates our hypothesis.

Numerous applications require tactile interfaces today. In particular, many customers' applications such as Smartphone, tablet PC or touch pad can be concerned by high performances, low voltage haptic interfaces which allow the user to interact with its environment by the sense of touch. This technology is already used but with limitations such as high power consumption and limited feedback effect (simple vibration). We chose to work on the squeeze-film effect. It consists in changing the friction between the finger and a plate resonator. It provides high granularity level of haptic sensation. This paper deals with the design of high performances actuators in order to promote the squeeze-film effect on a 4-inch plate (diagonal of the plate). Using predictive models, we select the best design, able to generate the highest substrate displacement amplitude as possible. We built demonstrators using a generic technology based on thin-film AlN actuators. Electromechanical characterization is ongoing before the integration of the thin-film actuator plate in a haptic demonstrator in a close future.

This paper reports on the development of a unique Digital Loudspeaker Array solution, based on Pb(Zr0.52,Ti0.48)O3 (PZT) thin-film actuated membranes, arranged in a matrix and which operate in a binary manner by emitting short pulses of sound pressure. Using the principle of additivity of pressures in the air, it is possible to reconstruct audible sounds. For the first time, electromechanical and acoustic characterizations were reported on 256 MEMS membranes DLA. Sounds audible as far as several meters from the loudspeaker have been generated using low-voltage.

This paper reports on the development of a Digital Loudspeaker Array (DLA) solution based on Pb(Zr0.52,Ti0.48)O3 (PZT) thin-film actuated membranes. These membranes called speaklets are arranged in a matrix and operate in a binary manner by emitting short pulses of sound pressure. Using the principle of additivity of pressures in the air, it is possible to reconstruct audible sounds. For the first time, electromechanical and acoustic characterizations are reported on a 256-MEMS-membranes DLA. Sounds audible as far as several meters from the loudspeaker have been generated using low voltage (8V).

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.

We present the development of a technological platform dedicated to 3D capacitive inertial sensors. The proof of concept will be made on a 3D gyroscope. The mobile structure is made within a 30 µm thick Si top layer of a SOI substrate, while poly-Si deposited on top of a sacrificial PSG layer serves as suspended top electrodes and connection wires. This technology enables us to maintain low parasitic capacitance, which is of paramount significance for capacitive detection. After packaging and association with an analogue electronic board, functionality of the sensor is demonstrated.

This paper describes the conception, designs consideration and fabrication process of a novel MEMS microphone. The presented microphone not only uses a new architecture, the sensitive part being beams moving within the plane of the substrate, but also uses an innovative detection means with Silicon piezo-resistive nanogauges. Modelization will consider acoustic and mechanical interactions. Besides, at MEMS scale, accurate simulation of the sensor must take into account thermal and viscous boundary layers in acoustics, and we will show that the presented sensor takes benefit from these short scale effects, which leads to achieve theoretical resolution as low as 24dB.

The MEMS digital loudspeaker consists of a set of acoustic transducers, called speaklets, arranged in a matrix and which operate in a binary manner by emitting short pulses of sound pressure. Using the principle of additivity of pressures in the air, it is possible to reconstruct an audible sound. MEMS technology is particularly well suited to produce the large number of speaklets needed for sound reconstruction quality while maintaining a reasonable size. This paper presents for the first time the modeling, realization and characterizations of a piezoelectric digital loudspeaker based on MEMS technology. Static, dynamic and acoustic measurements are performed and match closely with theoretical results.

A new way to detect a leakage in packaging for micro-mechanical sensors by using hydrophilic porous ultra low k dielectric components has been developed. Two synthesis means are used to deposit nanoporous SiOCH (PECVD) and MSQ (Spin Coating) with additional dedicated process to obtain high open porosity with an average pore radius distribution around 1 nm. The characterizations of the porous dielectric layers deposited on two electrodes with interdigitated fingers for capacitive measurements show a very high sensitivity to 51 % RH atmospheric air. Measurements show a 2% capacity variation for 1 ppm moisture. The process is CMOS compatible.

The integration of high-performance RE-TM (NdFeB and SmCo) hard magnetic films into micro-electro-mechanical-systems (MEMS) requires their patterning at the micron scale. In this paper we report on the applicability of standard micro-fabrication steps (film deposition onto topographically patterned substrates, wet etching and planarization) to the patterning of 5–8μm thick RE-TM films. While NdFeB comprehensively fills micron-scaled trenches in patterned substrates, SmCo deposits are characterized by poor filling of the trench corners, which poses a problem for further processing by planarization. The magnetic hysteresis loops of both the NdFeB and SmCo patterned films are comparable to those of non-patterned films prepared under the same deposition/annealing conditions. A micron-scaled multipole magnetic field pattern is directly produced by the unidirectional magnetization of the patterned films. NdFeB and SmCo show similar behavior when wet etched in an amorphous state: etch rates of approximately 1.25μm/min and vertical side walls which may be attributed to a large lateral over-etch of typically 20μm. Chemical–mechanical-planarization (CMP) produced material removal rates of 0.5–3μm/min for amorphous NdFeB. Ar ion etching of such films followed by the deposition of a Ta layer prior to film crystallization prevented degradation in magnetic properties compared to non-patterned films.

This paper reports on the electrodeposition at room temperature and the characterization of hard magnetic CoPtP material. An acidic bath has been set up to be compatible with the use of photoresist for micro technologies processes. X-ray diffraction (XRD) diagrams show that CoPtP alloy crystallizes in the hexagonal system. The film growth is generally columnar with a pronounced < 0 0 2 > texture associated with preferential out-of-plane magnetization. Using particular electrodeposition conditions, in-plane magnetization can be recovered and coercivities as high as 2800 Oe are reached for patterned layers. So a room temperature electroplating process able to produce patterned micromagnets usable in magnetic applications has been set up. Examples of the integration of CoPtP micromagnets are described through the fabrication of three devices: a multilayered giant magneto-resistive sensor biased by five electroplated magnets, a vertical magnetic bistable microactuator and a horizontal magnetic bistable microswitch. The main challenge for the last two devices was to demonstrate the actuation of a moving micromagnet without any mechanical guiding during commutation. The demonstrated bistability provided by the use of micromagnets emphasizes the interest in these devices for many applications.

A new magnetic micro-actuator with integrated permanent magnets has been developed. The design of this device, with a levitating mobile magnet, is a real innovation and is patented. The structure was modeled using analytical and numerical calculations. Furthermore, the fabrication feasibility, using collective micro-technology processes, has recently been demonstrated.