Linearity Improvement of MEMS Electrochemical Vibration Sensors Based on Tapered-Hole Technology

Electrochemical vibration sensors offer high sensitivity, low mechanical noise, and superior low-frequency performance, making them attractive for applications such as seismic detection and underwater acoustic sensing. However, existing electrochemical seismometers, angular accelerometers, and vector hydrophones primarily focus on sensitivity and noise, while sensor linearity-especially across wide frequency ranges-remains insufficiently investigated. In practice, linearity degradation frequently occurs at low and high frequencies due to diffusion limitations of electroactive species in the electrolyte. In this study, the linearity mechanism of electrochemical vibration sensors is analyzed, and two key structural parameters affecting linearity are identified: one is the anode-cathode spacing and the other is the effective cathode length. To improve linearity, an electrochemical sensing electrode incorporating an ultra-narrow insulating ring and a tapered micro-orifice is proposed. Finite element simulations are performed to evaluate the effects of electrode spacing, orifice geometry and excitation frequency. The sensor is fabricated using MEMS fabrication technology and experimentally characterized. Results show a peak sensitivity of 1242 V/(m/s) and excellent linearity within an input velocity range of 0.0002-0.012 m/s at 5 Hz, 10 Hz, 40 Hz and 100 Hz, with correlation coefficients exceeding 0.998. The proposed design provides an effective approach for linearity enhancement in electrochemical vibration sensors.