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.