MEMS short-period chip-level seismometer for the next generation Lunar/Mars seismograph

China's Lunar Exploration Program aims to deploy advanced seismometers on the lunar surface for detecting and characterizing moonquakes, essential for understanding the Moon's internal structure. Compared to conventional seismic geophones, nano‑g‑resolution MEMS accelerometers offer superior sensitivity, compact size, and low power consumption—key attributes for space instrumentation. This paper presents a capacitive MEMS accelerometer designed for next‑generation lunar seismometry. Its sensing element consists of a movable silicon proof mass suspended by micromachined beams, with distributed capacitive electrodes detecting minute displacements.

Innovating beyond traditional parallel‑plate designs, a corrugated electrode structure reduces the second‑order nonlinear coefficient by half and the third‑order coefficient by two‑thirds, improving linearity without compromising footprint or sensitivity. Furthermore, the device incorporates an electrostatic negative stiffness mechanism, successfully reducing the intrinsic resonant frequency to 122 Hz. The decrease in resonant frequency improves the mechanical gain of the seismometer, thereby enhancing the instrument's sensitivity. The design also improves pull‑in stability, extending the operational measurement range.

Comprehensive experimental characterization validates the device's performance:

• The fabricated short-period (SP) seismometer achieves a low noise floor of 7 ng/√Hz within the 0.5–3.5 Hz band, which is crucial for detecting faint seismic signals.
• It exhibits a broad linear measurement range of ±34 mg and a high open-loop dynamic range of 134 dB. 
• The device provides a –3 dB bandwidth of 180 Hz, supporting a wide frequency response.
• Notably, its extreme miniaturization—with a MEMS die measuring only 5.2 mm × 6.5 mm and a mass under 20 milli-gram—makes it particularly suitable for weight-sensitive lunar missions.

This research has not only developed a high‑sensitivity MEMS sensor suitable for lunar seismology, but also holds significant potential for terrestrial geophysical applications such as precision seismic monitoring and oil‑gas exploration. The design provides a promising and robust technical pathway for the future development of high‑performance closed‑loop MEMS accelerometers.

Fig 1 The schematic view of the proposed MEMS accelerometer system

Fig 2 Noise performance of the proposed MEMS accelerometer in an open-loop configuration, in which the self-noise is the actual noise floor of the proposed device, with the elimination of the influence of Earth tremors.