Norbert Dumas

Modeling the influence of etching defects on the sensitivity of MEMS convective accelerometers

In this paper, a behavioral model that includes the influence of etching defects on the sensitivity of MEMS convective accelerometers is presented. Starting from an existing behavioral model, new physically-based expressions have been derived to introduce etching defects in the simulation of thermal conduction in the sensor. In addition, a semi-empirical model has been introduced for thermal convection. Finally, a very good agreement is obtained between the behavioral model and FEM simulations.

Investigations on electrical-only test setup for MEMS convective accelerometer

In this paper, we investigate potential solutions for the development of an electrical-only test procedure for MEMS convective accelerometers. The objective is to define an alternative low-cost test procedure applicable at wafer-level. Simple electrical test measurements are analyzed and a behavioral model allowing fault injection is developed. Simulation results show that most of the parametric faults that affect the device specifications can be detected with electrical measurements. Only faults that affect the convective behavior escape this alternative test. A preliminary study of convective effects using FEM simulation is then conducted to identify the key parameters that should be included in the model for the subsequent definition of adequate electrical test parameters.

An electrical test method for MEMS convective accelerometers: Development and evaluation

In this paper, an alternative test method for MEMS convective accelerometers is presented. It is first demonstrated that device sensitivity can be determined without the use of physical test stimuli by simple electrical measurements. Using a previously developed behavioral model that allows efficient Monte-Carlo simulations, we have established a good correlation between electrical test parameters and device sensitivity. Proposed test method is finally evaluated for different strategies that privilege yield, fault coverage or test efficiency.

Design of a micromachined CMOS compass

This paper presents the design of a low-cost monolithic CMOS microcompass. The system is based on a cantilever actuated by the Lorenz force. Conditioning circuitry has been designed carefully to reject noise, to eliminate parasitic phenomena such as thermal effects, and to be robust to process scatterings without the need of an external trimming. Mixed-mode simulations have been enabled using a behavioral description of the sensor, and validations of the complete system have been performed. The expected performance has a resolution inferior to 1/spl deg/ for a total surface of 10.6mm/sup 2/ and a power consumption of 56mW (without the digital processing bloc).

A CMOS Multi-sensor System for 3D Orientation Determination

This paper presents a unique combination of magnetic and inertial MEMS sensors on a fully monolithic CMOS chip. Pitch and roll are measured using two identical heat transfer based tilt sensors while yaw is derived from an original electromechanical compass. For complete 3-D positioning, the use of an additional z-axis piezoresistive accelerometer is also investigated. Contrary to systems based on gyroscopes, the proposed device outputs the absolute values of the three Eulerpsilas angles. All sensors (i.e. the magnetometers, the thermal tilt sensors, and the z-axis accelerometer) are fabricated simultaneously using a cheap one-step auto-aligned post process (front side bulk micromachining), thus addressing consumer markets for very low-cost applications. Prototypes have been designed and characterized for each sensor. The measured resolution is about 1.7deg for pitch and roll with a time response of 30 ms and 2deg for yaw with a time response of only 10 ms. The targeted overall surface is around 10 mm while power consumption is approximately 50 mW when operated continuously. Such sensors association has numerous identified applications in the field of mobile devices: compass with tilt compensation; pointing devices, new functionalities in mobile phones to mention few.

An approach to integrate MEMS into high-level system design flows

MEMS integration into standard design flows is still an open topic after several years of research and investigations. Facing the diversity of CAD tools, modeling languages and associated simulators, the choice of a particular design flow seems to be a matter of culture. The work presented demonstrates how, in a microelectronic environment, it is possible to focus on system level simulation taking into account MEMS integration. The study is illustrated on a convective accelerometer fabricated on a CMOS technology. Various issues concerning the design of such system are addressed, from the low-level modeling of the sensing device to system level design of a delta-sigma modulator. Example of MEMS integration into the Cadencereg and Matlabreg environments are provided.

Test and calibration of MEMS convective accelerometers with a fully electrical setup

MEMS devices are expected to be used in a growing number of high-volume and low-cost applications. However because they typically requires the application of physical test stimuli to verify their specifications, test and calibration costs are actually a bottleneck to reduce the overall production cost of MEMS sensor. This paper presents an alternative electrical-only solution for testing and calibrating the sensitivity of MEMS convective accelerometers. It is based on simple impedance measurements performed both at ambient temperature and under nominal biasing conditions. The method is evaluated through Monte-Carlo simulations considering typical process fluctuations and mismatch. Results show the potentialities of the technique that permits to reduce the dispersion of sensitivity by a factor higher than 11 after calibration. As a consequence, a production yield of more than 99.8% can be expected for low-cost products using only electrical measurements for the calibration scheme.

An A/D interface for resonant piezoresistive MEMS sensor

This paper introduces an original architecture to measure and convert into digital data the oscillations of a resonant beam. An electromechanical CMOS magnetic field sensor is considered here for the purpose of a case study. The proposed architecture is based on counting the cycles of an oscillator output, whose frequency depends on the deformation of the mechanical structure. In order to reduce drifts, the architecture implements a differential measure by using both up and down counting within a mechanical vibration period, using the actuation signal for synchronization. Simulation results demonstrate that a high resolution can be achieved with acceptable integration time. Such a signal processing architecture is particularly suitable for low-cost CMOS mechanical structures.