Abstract-The work presents the principle and the complete characterization of a single-chip unit formed by MEMS magnetometers to sense the 3D magnetic field vector, and a Tang resonator. The three sensors, nominally with the same resonance frequency, are operated 200 Hz off-resonance through an AC current whose reference frequency is provided by the resonator, embedded in an oscillating circuit. The sensors gain is increased by adopting a current recirculation strategy using metal strips directly deposited on the structural polysilicon. At a driving value of 100 µArms flowing in series through the three devices, the magnetometers show a sub 185 nT/ √ Hz resolution with a selectable bandwidth up to 50 Hz. Over a ± 5 mT full-scale range, the sensitivity curves show linearity errors lower than 0.2%, with high cross-axis rejection and immunity to external accelerations. Under temperature changes, stability of the 200-Hz difference between the magnetometers and the resonator frequency is within 55 ppm/K. Offset is trimmed down to the µT range, with an overall measured Allan stability of about 100 nT at 20 s observation time.

This paper reports the developments towards an integrated, triaxial, frequency-modulated, consumergrade, MEMS gyroscope. A custom low-power (160 µA), low-phase-noise integrated circuit is designed specifically for frequency-modulated operation. Both yaw-and pitchrate sensing systems are demonstrated, by coupling the circuit with two novel micromachined structures fabricated with a 24-µm-thick industrial process. In operation, both gyroscopes show a repeatable and stable scale factor, with less than 0.55% of part-to-part variability, obtained without any calibration, and 35 ppm/ • C of variability over a 25 • to 70 • C temperature range.

W HILE THE consumer market forecasts for singleparameter microelectromechanical systems (MEMS) inertial sensors begin to flatten, the forecasts for multiparameter inertial measurement units (IMUs or combo sensors) are still indicating a large growth for the next years [1]. This implies that issues like the cointegration of different sensors within the same industrial process and package will become more and more relevant, particularly in consumer applications where area and assembly cost play a major role in the competition.Cointegration of MEMS accelerometers and gyroscopes in the same package was made possible through different strategies in scientific researches [2]-[4] and industrial products [5], [6]. However, ten-axis IMUs-integrating a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, and a pressure sensor-are still based on different production processes for the different sensors. In particular, for the case of magnetometers, technologies other than micromachining are widely adopted, including, for the specific case of consumer Manuscript

The work presents a microelectromechanical system (MEMS) based magnetometer, targeting compass applications performance, which measures magnetic fields along an in-plane direction. The magnetometer is fabricated with the surface micromachining process used for consumer gyroscopes, accelerometers, and recently proposed out-of-plane magnetometers. The magnetometer is based on the Lorentz force principle, so to avoid the need for magnetic materials integration. It features an area of 282 x 1095 µm 2 , and it is wafer-wafer packaged at a nominal pressure (0.35 mbar) similar to the one used for gyroscopes. In agreement with theoretical predictions, operation is demonstrated both at-resonance and off-resonance: in both situations the measured resolution, normalized to unit bandwidth and applied Lorentz current, is about 120 nT·mA/ √ Hz, but the maximum sensing bandwidth is extended from 4 Hz (at resonance) to 42Hz in off-resonance mode, which copes with consumer specifications. Within magnetic fields of ±5 mT, the device shows measured linearity errors <0.5% of the full-scale-range (demonstrating a large linearity) and a cross-axis rejection of ∼50 dB. The bias stability in off-resonance operation mode (80 nT·mA at 100 s) improves by a factor 100 with respect to resonance operation.

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