A Biaxial MEMS Capacitive Nanoforce Sensor Based on a Novel Bistable Bioinspired Swallow Structure for Somatic Cell Micromanipulation

Precise measurement of ultralow biaxial forces at the nano-Newton (nN) level is highly demanded for robotic micromanipulation of somatic cells. A novel microelectromechanical system capacitive nanoforce sensor was proposed to address this demand. Inspired by the stable gliding gestures of a swallow, a bistable swallow structure was introduced, offering high deformation flexibility with negligible mechanical cross-axis coupling. Considering its mechanical behaviors, a comb configuration and interconnection strategy were proposed to eliminate internal electrostatic coupling rotation. The fabricated sensor was packaged with a time-division multiplexing-based readout circuit, comprising a compact measurement system. Thex-axis force sensitivity reached 0.9893 fF/nN, with a high resolution of 0.3658 nN and a linearity of 0.9994 over a range of 8.02 μN. Besides, they-axis force sensitivity reached 0.2683 fF/nN, with a resolution of 0.8244 nN and a linearity of 0.9995 over a range of 8.11 μN. The noise floor was lower than 0.0665 nN/$\sqrt {\mathbf{Hz}} $and 0.1688 nN/$\sqrt {\mathbf{Hz}} $forx-andy-axes, respectively, and the cross-axis coupling error ratios were only 0.15% and 0.36%, respectively. The proposed sensor was adopted to manipulate mouse myoblast cells, allowing nN-level biaxial interaction force responses to be measured in real-time robotic manipulation for the first time.