Design, Fabrication, and Control of a Double-Stage MEMS Force Sensor

This article presents a novel double-stage microelectromechanical systems (MEMS) force sensor fabricated using a silicon-on-insulator process. The sensor comprises two stages. An inner stage that performs force sensing and an outer stage functioning as a bidirectional positioner for the inner stage. Through the integration of on-chip actuation and sensing mechanisms, the sensor enables closed-loop operations, ensuring precise force sensing and positioning. To enable adaptability to different samples, an electrostatic actuator structure is integrated into the force sensing stage to allow for stiffness adjustment. Operating in closed loop, the inner stage force sensor achieves a 1
$\sigma$
-resolution of 4.67 nN and a full-scale range of
$\pm$
138.7 
$\mu$
N. The nanopositioner provides a linear travel range of 5.3 
$\mu$
m and an ultimate displacement of 8 
$\mu$
m. To evaluate force sensor's closed-loop performance, a set of experiments is conducted aiming to measure the stiffness of four distinct samples using two deflection waveforms generated by the on-chip nanopositioner.