A wide-bandwidth tri-axial pendulum accelerometer with fully-differential nano-gap electrodes

This paper presents the implementation and characterization of a single proof-mass wide-bandwidth pendulum accelerometer with fully-differential sensitivity in all three axes. The utilization of nano-gap electrodes (300 nm) boosts the electromechanical coupling significantly so that both increased sensitivity and high resonant frequency ( f res > 15 kHz) can be attained, which extends the operational bandwidth as well as the dynamic range of the device using a miniaturized proof-mass of 450 × 450 µ m 2 . Furthermore, increased air-damping from the nano-gap structure enables the stable operation of the device at moderate vacuum environment (1–10 Torr), which paves the way toward the single-chip inertial measurement unit by integrating a quasi-static accelerometer with resonant gyroscopes on a common substrate. The presented design is fabricated on a 40 µ m thick silicon-on-insulator substrate and wafer-level vacuum-packaged with a TSV substrate at a moderate vacuum level (1–10 Torr). The device, interfaced with a switched capacitor ASIC exhibits sub-milli-g noise levels in a wide bandwidth exceeding 10 kHz and bias instability of 560 µ g, 428.16 µ g, 145 µ g for the X , Y and Z axes, respectively.