A 0.5 mm2 integrated capacitive vibration sensor with sub-10 zF/rt-Hz noise floor

This paper presents a 1-axis vibration sensor that integrates hermetically sealed micromechanical structures and BiCMOS circuits. Close integration of the micromechanical structures with sense circuits, and an area-efficient sensing scheme lead to smaller mechanical structures and, therefore, a small die size and a low manufacturing cost. Circuit techniques are used to compensate for mechanical nonidealities. Correlated double sampling (CDS) based capacitance sensing circuits with on-chip regulator for reference voltage generation and a capacitive DAC based offset cancellation circuit are presented. The sense circuits achieve a noise floor of less than 10 zF/rt-Hz with a sensitivity of 0.5 mV/aF, while drawing 2 mA. The self-contained IC, implemented in a 0.5 μm BiCMOS process is 0.5 mm² in area and is packaged in a 8 pin SOIC. The capacitance noise floor and the die area per sense axis are better than known state-of-the-art by a factor of 2. The vibration sensor achieves a noise floor of 400 μG/ rt-Hz, with a sensitivity of 10 mV/G and a resonance frequency of 22 kHz. A sensor pair set up to measure rotational vibrations in hard disk drive applications, achieves a noise floor of 10 rad/s² in 7 kHz bandwidth with a separation of 80 mm.