Guillaume Jourdan

3D Magnetic Field Sensor Concept for Use in Inertial Measurement Units (IMUs)

We report on the design, fabrication, and characterization of a microfabricated 3D magnetic field sensor that is suitable for co-integration with inertial sensors to form single-chip inertial measurement units. In contrast to classical resonant MEMS magnetometers, which are based on Lorentz force measurement, our sensor uses permanent magnetic materials and piezoresistive detection with silicon strain gauges of nanometric section, leading to low power consumption and high sensitivity for small sensor size. Thin multilayers of CoFe and PtMn as ferro- and antiferromagnetic materials are integrated within the MEMS fabrication process. Sensitivities of 1.09 V/T for x- and y- components of the magnetic field and 0.124 V/T for z- component of the magnetic field were measured, respectively. To be sensitive to magnetic fields along all three spatial directions, two permanent magnetization directions on the same die are required. Implementation of the two magnetization directions was validated by a measured correlation of 99.7% between x- and y- sensitivity axes. Power consumption of the 3D sensor is for polarization with a 100 μA dc current. With resolutions of 100 nT/√Hz for x- and y-component of the magnetic field and 350 nT/√Hz for z- component, the sensor is suitable for precise measurement of earth magnetic field.

A novel microfabricated high precision vector magnetometer

We present a novel 3-axis MEMS-based vector magnetometer with integrated magnets and piezoresistive detection using silicon nano-gauges. Sensitivities of 9V/T and resolutions below 10nT/√Hz can be achieved with an exceptionally low power consumption of less than 10µW. We have experimentally validated this new magnetometer concept and obtained sensitivity values which were are in good agreement with design. Two perpendicular magnetization axes were integrated in the chip plane in order to achieve 3-D sensitivity. A very high correlation of 99.8% between sensitivities to perpendicular magnetic field components in the chip plane was measured, which makes this sensor highly precise in vectorial measurement of magnetic fields.

Low power damping control of a resonant sensor using back action in silicon nanowires

This paper reports the damping control of a MEMS resonator, vibrating at several kilohertz, using tiny p-doped piezoresistive silicon nanowires (SiNW). Due to thermal piezoresistive back action (TPBA), DC-current biasing of the nanobeams induces a strong increase of the damping rate, about 2 decades above the intrinsic damping rate of the resonator. Intrinsic quality factor (QF) around 3.104 is here reduced to 450 thanks to an outstanding efficient TPBA. It is worth noting that QF can be here finely controlled for DC-current as low as a few tens μA, which leads to very low power consumption at constant voltage generator circuitry. This property is highly suitable for numerous applications, such as amplitude modulated resonant sensors (gyrometers, accelerometers...) or high performance resonant sensors, for which an accurate and repeatable control of the QF is required. Furthermore, the proposed mechanism allows bandwidth tuning and temperature compensation of the QF, without inducing parasitic crosstalk signals.

Electromechanical damping in MEMS accelerometers: A way towards single chip gyrometer accelerometer co-integration

This paper reports a method for controlling mechanical damping in MEMS devices. It consists in coupling a micro resonator to an electrical resistance that provides an additional damping source. Quality factor of individual MEMS can then be individually controlled. Quality factor tuning offers an efficient solution to solve the co-integration issue of accelerometer with gyrometer inside a same MEMS cavity under low pressure.

Ultra-compact and highly sensitive pressure sensor based on nano-gauge detection and cointegrated with inertial sensors

This paper reports for the first time the experimental pressure response of an ultra-compact and highly linear absolute pressure sensor based on suspended piezoresistive nano-gauges with mechanical amplification and embedded low voltage self-test. Nano-gauges being suspended and structurally protected from the external environment, it can be used in high temperature and harsh environments. Unidirectional and amplified stress on the nano-gauges allows drastic miniaturization (0.12mm2 footprint for a 1 bar structure). In addition, the M&NEMS technology used for the manufacturing enables its direct cointegration with inertial sensors.

Transduction performance of piezoresistive silicon nanowires on the frequency resolution of a resonant MEMS sensor

In this paper, we study the resonance frequency resolution of a MEMS resonator based on suspended piezoresistive silicon nanogauges transduction. Nanowire strain gages are attractive for MEMS resonators thanks to their high sensitivity to motion. They have excellent force sensitivity due to their small cross-section area (250×250nm2) and a negligible footprint. Hence, this transduction mean exhibits a very high signal to noise ratio (SNR) of 115dB above a few kHz, which does not limit the excellent resolution frequency required for high performance applications. Thus, resolution frequency down to 35 ppb is here reported, limited by thermo mechanical fluctuations, instrumentation noise and environment stability. Influence of various actuations and damping conditions are investigated and then compared to the Robins law that estimates resolution for the frequency measurement. Thus, Robins law is validated for the nanogauge transduction of a MEMS resonator. Eventually, these results can be used to anticipate the outstanding frequency resolution of an ongoing resonant pressure sensor, which has been estimated at only a few ppb.