Denis Janiaud

A New Quartz Monolithic Differential Vibrating Beam Accelerometer

This paper deals with a new monolithic differential quartz Vibrating Beam Accelerometers (VBA), called VIASC. The concept of this accelerometer includes the three major insulation requirements of the beams in the same quartz monolithic structure: insulation of the beams against thermal stresses, insulation of the beam vibrations and insulation between the two beams. In this paper, the concept of this accelerometer and its manufacturing process by chemical etching are presented. Preliminary results, which confirm the relevance of the VIASC concept, are given and future work on the sensing element is discussed. Two VIASC developments are envisaged: an accurate VIASC version compatible with inertial navigation requirements and a miniaturized version adapted to guidance applications.

The VIA vibrating beam accelerometer: concept and performance

The micro-machined quartz vibrating beam accelerometer, VIA (Vibrating Inertial Accelerometer), has been developed in ONERA aiming at civil and military purposes. The present applications of this device are the guidance and the attitude control of tactical missiles as well as the aircraft inertial navigation. High accuracy, 10/sup -5/ to 10/sup -6/ of the measurement range, and low cost manufacturing are thus demanded. The VIA concept has been selected to meet these objectives. First, the monolithic configuration of the transducers is well suited to chemical etching process and miniaturization. Secondly, the choice of vibrating beams as sensitive elements, combined with excellent quartz mechanical properties, gives a very good stability of the scale factor. The performed optimisation of the transducer leads to a very good insulation of the active part, included a proof mass, a vibrating beam and two articulations, with respect to the mounting areas of the transducer. The insulation has been obtained by a flexible frame, inserted between the active part and the mounting areas. The VIA accelerometer is composed of two transducers and two oscillating loops. A differential arrangement is needed in order to reduce in particular the thermal sensitivity. The two beam frequencies are about 60 kHz and the accelerometer scale factor is 24 Hz/g.

A 50 nano-g resolution quartz Vibrating Beam Accelerometer

This paper reports the design, realization and test of a 50 nano-g resolution Vibrating Beam Accelerometer (VBA). Based on the VIA or DIVA quartz vibrating beam accelerometers, dedicated for tactical applications (±100 g measurement range, 300 μg repeatability, all errors combined), this work explores the improvement of the VBA resolution by reducing the measurement range to ±10 g, targeting navigation applications for lower dynamic vehicles.

The fairy world of quartz vibrating MEMS

Quartz crystal has been an essential material for time and frequency and radio-frequency applications during the 20th century. Quartz is always an unmatched material at the beginning of the 21st century, and hold 80 % of oscillators & RF market which represent today 17 billions market with a 10 % growth per year. This paper describes other more confidential applications - the vibrating inertial MEMS - where the quartz crystal plays also a major role. Clearly, quartz crystal has still a future in these high added value applications, and for a long time.

A new analog oscillator electronics applied to a piezoelectric vibrating gyro

This paper deals with a new analog oscillator applied to a piezoelectric vibratory gyroscope developed at ONERA. The equivalent circuit of the gyro and the readout electronics are presented. Then, the influence of phase and amplitude drifts of the drive mode vibration on the angular velocity measurements are discussed theoretically and experimentally. Finally, simulations of the new analog oscillator electronics including phase and amplitude control loops are shown.

The VIA vibrating beam accelerometer: a new quartz micromachined sensor

ONERA, the French National Establishment for Aerospace Research, under the financial support of the DGA (The French MoD Procurement Agency), has been developing a micro-machined quartz vibrating beam accelerometer called VIA (Vibrating Inertial Accelerometer). This sensor exploits the frequency change of a quartz resonator when submitted to an acceleration. The main targeted applications are the guidance and the attitude control of tactical missiles, as well as the inertial navigation of aircraft, helicopters and ground vehicles (coupled with radio-electric positioning systems such as the GPS receiver). The VIA concept has been selected to meet these objectives. First, the monolithic configuration of the transducers is well suited to chemical etching process and miniaturization. Secondly, the choice of vibrating beams as sensitive elements, combined with excellent quartz mechanical properties, gives a very good stability of the scale factor. Third, the performed optimisation of the transducer leads to a very good insulation of the active part with respect to the mounting areas of the transducer, suitable to bias stability. In order to reduce the thermal sensitivity, the accelerometer is composed of two transducers operating in differential mode.

An integrated resonator-based thermal compensation for Vibrating Beam Accelerometers

Although the Vibrating Beam Accelerometer (VBA) shows excellent performances (resolution <; 1 μg), its bias drift over temperature and temperature gradient is a main performance limitation. Numerical compensation can be performed with a temperature sensor in the accelerometer package, but this approach shows two drawbacks for fast measurements: first, there is a time delay between the temperature of the vibrating beam and the temperature of the package, and second the noise level is very high. In order to overcome these limitations, a new structure comprising a second resonator in torsional mode placed in the middle of the vibrating beam was designed. It shows good sensitivity and linearity over temperature and senses the instantaneous temperature of the vibrating beam with low noise, allowing a better compensation of thermal drifts. A new accelerometer with resonator-based thermal compensation was designed, realized and tested. Experimental results confirm the excellence of the torsional mode resonator used as a temperature sensor.

A micromechanical resonator to reach the quantum regime

We present a new micromechanical resonator designed for the observation of its quantum ground state (QGS). To reach QGS, a high frequency resonator with the lowest possible mass and the highest possible quality factor, coupled with an extremely sensitive measurement technique, has to be implemented. Using a high-finesse Fabry-Perot cavity with a mirror coated on the resonator, we expect benefits from the unique sensitivity of optical interferometry (10−38 m2/Hz) and from the optomechanical coupling between the light and the micro-resonator both to laser cool the resonator down to its ground state and to observe its residual quantum position fluctuations. We present the resonator we have developed for that purpose, which takes advantage from the high intrinsic quality factor of single crystal quartz and is designed to obtain a high resonance frequency (a few MHz) as well as a low mass (a few tens of µg). A length extension mode is used in order to avoid any deformation of the mirror surface and so to preserve the intrinsic quality factor of the resonator. A dedicated crystallographic orientation and a beam equilateral cross-section have been defined with respect to the quartz trigonal symmetry, allowing the micromachining of the resonator by wet etching. A beam cross-section area of 10−2 mm2 has been chosen to ease the deposit of the multilayered mirror. First mechanical characterizations of the resonator give a resonance frequency of 3.6 MHz, with a 25 µg mass and a quality factor of 390 000. Next steps will be the coating of the low-loss mirror on the resonator and its implementation in the Fabry-Perot cavity.

Behavioral Modelling of Vibrating Piezoelectric Micro-Gyro Sensor and Detection Electronics

This paper describes the development of a model of vibrating piezoelectric micro-gyro sensor using analog hardware description. Our procedure implies several steps with emphasis in model complexity reduction and identification of critical parameters. The proposed macro-model permits multi-physic simulations including mechanical, piezo-electric and electrical analytic descriptions and allows a top-down development approach. As a tool for coding our descriptions, we use analog hardware description language (Verilog-A). For achieving the behavioural computation results, CADENCE simulation environment was used. The critical parameters of the gyro are then studied: the output noise, the output bias and scale factor stability over temperature.

Quartz resonator for MEMS oscillator

A three-dimensional length-extension mode (3D-LEM) resonator has been developed for fundamental physics purpose showing a very good frequency stability potential highlighted by a Quality factor Frequency product (Q.F) above 1013. Those characteristics are quite interesting for time & frequency applications but since a 3D structure is difficult to integrate, a planar two-dimensional (2D) resonator approach is now undertaken. Because of the intrinsic quartz high quality factor and good thermal stability, this new resonator shall be able to challenge silicon resonator based MEMS oscillator with comparable dimensions. It will furthermore respond to the need for simple collective machining and flat pack packaging. This paper focuses on the theoretical study of this new 2D-LEM resonator. The first part is about defining the best geometric compromises and mounting area designs to meet high quality factor requirements. This was made through Finite Element Modeling (FEM). Two quartz cut oriented perpendicular to X and Z crystallographic axes have been compared with adapted actuation electrodes systems to analyze the thermal sensitivity and the motional resistance thanks to the OOFELIE Multiphysics FEM software. An estimate of the phase noise level is also presented. To collectively process such small resonators Deep Reactive Ion Etching (DRIE) on quartz wafer bonded substrates is currently being developed.