Low-Pressure Small MEMS Accelerometer Using Sigma-Delta Modulation

Abstract

Encapsulation of MEMS accelerometers in vacuum is advantageous, since it allows integration with other sensors, leading to size and cost reduction. One technique to operate MEMS accelerometers in vacuum is the use of closed-loop Sigma-Delta modulation, which has many advantages. In this paper, the design of a vacuum encapsulated small size MEMS accelerometer (0.2 mm2) and the preliminary measured results are presented. Experimental devices were fabricated and operated in 2nd and 3rd order Sigma-Delta modulators, achieving a noise figure of 389 µg/√Hz for a bandwidth of 200 Hz and a measurement range of at least ±1 g.

Highly sensitive MEMS frequency modulated accelerometer with small footprint

“…While, gyroscopes are generally encapsulated in vacuum because of the need of high-quality factors, open-loop capacitive accelerometers being sensitive to external vibrations (lack of vibration robustness), require more effort for closed-loop operation at low pressure [7]. Two alternatives can be used to address this limitation: the use of closed-loop approaches to keep the proof-mass at the central position using mechanisms such as sigma-delta [8], or frequency modulated devices [5,[9][10][11]. Resonant MEMS offer as main advantages a high dynamic range (no displacement limitation), immunity to pull-in and a quasi-digital output [9,11].…”