Servo-Assisted Position-Feedback MEMS Force Sensor with Tunable Sensitivity and Sub-Nanonewton Range

A Micro Electro-Mechanical System (MEMS) that allows to measure an external force applied to a probe tip exploiting an electrical servo-assisted mechanism based on position feedback is presented. The sensor architecture keeps the position of the probe tip fixed by driving a pair of variable-area electrostatic actuators in a feedback loop controlled by a variable-gap capacitive sensor. By adjusting specific loop parameters, the force sensitivity can be finely tuned electrically. Sub-nanonewton measurement range is achieved with high flexibility in setting the tip working point, making the system promising for measuring forces generated by living biological cells.