High Frequency top-down Junction-less Silicon Nanowire Resonators

We report here the first realization of top-down silicon nanowires (SiNW) transduced by both junction-less field effect transistor (FET) and the piezoresistive (PZR) effect. The suspended SiNWs are among the smallest top-down SiNWs reported to date, featuring widths down to ~20nm. This has been achieved thanks to a 200mm-wafer-scale, VLSI process fully amenable to monolithic CMOS co-integration. Thanks to the very small dimensions, the conductance of the silicon nanowire can be controlled by a nearby electrostatic gate. Both the junction-less FET and the previously demonstrated PZR transduction have been performed with the same SiNW. These self-transducing schemes have shown similar signal-to-background ratios, and the PZR transduction has exhibited a relatively higher output signal. Allan deviation AD of the same SiNW has been measured with both schemes, and we obtain AD~20ppm for the FET detection and AD~3ppm for the PZR detection at room temperature and low pressure. Orders of magnitude improvements are expected from tighter electrostatic control via changes in geometry and doping level, as well as from CMOS integration. The compact, simple topology of these elementary SiNW resonators opens up new paths towards ultra-dense arrays for gas and mass sensing, time keeping or logic switching systems in SiNW-CMOS platform

Biaxial piezoelectric MEMS mirrors with low absorption coating for 1550 nm long-range LIDAR

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.This research was funded by ECSEL Joint Undertaking (JU) grant number No. 826600 (project VIZTA).Peer ReviewedPostprint (published version

Suspended silicon nanowires resonating at high frequency : theoretical and experimental study

La miniaturisation des composants électroniques de l'échelle micro à l'échelle nano a entrainé aussi une miniaturisation des systèmes micro électromécaniques (MEMS). Cependant, la transition de MEMS à NEMS (systèmes nano électromécaniques) ne se résume pas simplement une réduction de taille. En fait, les méthodes d'actionnement et de détection utilisées couramment à l'échelle micro ne sont pas toujours efficaces à l'échelle nano. En plus, la fabrication des composants nanométriques avec des méthodes top-down est un défi à cause des limites de résolution. En surmontant ces difficultés, nous avons fabriqué et caractérisé des résonateurs à base de nanofils en silicium suspendus avec des petites sections de 30nm par 40nm et de longueurs allant de 1.5-3.5μm. L'actionnement de ces résonateurs est électrostatique et la détection est effectué avec deux mécanismes indépendants : (i) l'effet piezo résistif de deuxième ordre et (ii) l'effet de champ. Les mesures en régime statique nous ont permis de valider la présence de ces deux mécanismes et d'extraire les paramètres correspondants tels que le facteur de jauge et la transconductance du nanofil. Aussi, pour la première fois, ces deux principes ont été utilisés en alternance pour détecter la résonance du même nanofil. Les résultats obtenus avec ces transductions sont très prometteurs. La distinction entre les deux méthodes de transduction a été possible grâce à l'hétérodynage qui permet de sélectionner des phénomènes qui se produisent à la fréquence naturelle du dispositif ou au double de cette fréquence. Dans le but d'évaluer les performances de ces résonateurs pour de potentielles applications, nous avons mesuré la variance d'Allan. La stabilité de ces résonateurs pour des temps courts est du même ordre que celle des MEMS en silicium ce qui permet d'envisager l'utilisation de nanofils de silicium pour concevoir des bases de temps. Ces dispositifs nanométriques peuvent également être utilisés comme détecteur de masse avec des résolutions en masse de l'ordre du zgThe continuous miniaturization of electronics from micro to nano scale has impacted also the micro electromechanical systems (MEMS). However, the transition from MEMS to NEMS (nano electromechanical systems) is not only a matter of size. The actuation and detection principles used for efficient transduction at the microscale are not always efficient at the nanoscale. Also, top-down fabrication for nanometric devices becomes challenging due to resolution limits. Overcoming such difficulties, we were able to fabricate and characterize suspended silicon nanowire resonators with cross sections as small as 30nm by 40nm and lengths of 1.5-3.5μm. The actuation of these resonators was electrostatic, while the detection was performed with two independent physical phenomena: (i) the piezoresistive effect of second order and (ii) the field-effect. Measurements in static regime permitted us to validate the presence of these two mechanisms and extract related parameters such as the gauge factor and the nanowire transconductance. Then, for the first time, these two principles were used alternatively on the same silicon nanowire device for resonance detection and showed promising results. The distinction between the two was possible thanks to the down-mixed technique which could differentiate phenomena happening at the natural resonant frequency of the nanowire and twice this frequency. In order to evaluate the performances of these resonators, Allan deviation measurements were performed. It seems that the short-term stability of these devices is in the spectrum of other silicon MEMS devices for time reference applications and that potentially silicon nanowire resonators could be conceived for time keeping. Another potential application of these devices consists in mass sensing with mass resolutions close to the state of the art (<zg

Thermal piezoresistive back action in p-type silicon nanogauges based MEMS

session posterInternational audienc

Tuning the Anti-Phase Mode Sensitivity to Vibrations of a MEMS Gyroscope

This paper proposes a stiffness correction method to improve the resilience to vibration of a dual-mass MEMS gyroscope with a particular focus near the resonance frequency of the anti-phase drive mode (fDa), i.e., its operational mode. Because of its balanced shape, this operating mode is ideally insensitive to vibrations. However, fabrication imperfections generates a residual sensitivity to parasitic vibrations that can disturb normal operation of the sensor. This work shows that the application of a DC voltage (Vtr) at the drive actuation electrode enables to decrease this sensitivity by a factor of at least 30 because of the stiffness tuning of the dual-mass structure. Experiments are performed to confirm this assumption and an efficient stiffness correction method is proposed to improve device operation

Stiffness correction method for improving vibrations immunity of a MEMS tuning fork gyroscope

session Memories, MEMS, SensorsInternational audienc

Stiffness correction method for improving vibrations immunity of a MEMS tuning fork gyroscope

session Memories, MEMS, SensorsInternational audienc

Thermal piezoresistive back action enhancement using an innovative design of silicon nanobeam

session XI: ResonatorsInternational audienc

Resonant Accelerometers Based on Nanomechanical Piezoresistive Transduction

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 technolog