Novel Area-Changed Capacitive Methods for Simultaneous Displacement Transducing and Force Balance in a Nano-g MEMS Accelerometer

High-precision MEMS accelerometers with nano-g resolution are emergent instruments for geophysical applications and proved their competence in terms of functionality. The electromagnetic actuator, which serves as an auxiliary component in nano-g MEMS accelerometers for improving the dynamic response, faces the challenges of process incompatibility, temperature sensitivity, and large form factor. Thereby, this paper proposes an area-changed capacitive method for both displacement transducing and force balance in a nano-g MEMS accelerometer, aiming to address those posed challenges and provide favourable performance. Thanks to the allowed large displacement range in the sensitive direction of the proposed device, the area-changed capacitive mechanism is able to be integrated with a highly-sensitive quasi-zero stiffness spring-mass structure. As a result, the fabricated force-balance MEMS accelerometer attains a calibrated self-noise of 1.3 ng/root Hz, which is one of the most sensitive MEMS-based accelerometers reported to date. The settling time, on the other hand, is reduced to 0.5 s with the electrostatic closed-loop control featuring the proposed subject, compared to 15.7 s in the open-loop configuration. In addition, the critical acceleration input at the boundary of the "pull-in" is calculated as 5.4 g, which is adaptable to most geophysical applications. This work is of considerable potential in geophysical applications such as earthquake monitoring or gravity measurements, and promising a high-performance closed-loop MEMS accelerometer.