Design and Implementation of a Bistable Force/Acceleration Sensing Device Considering Fabrication Tolerances

We report on a design methodology, fabrication, and characterization of a bistable actuator operated by a parallel-plate electrostatic transducer. The operational principle of the device, which can serve as a bifurcation-based contact-free force/acceleration sensor, is based on a pull-in voltage monitoring. Bistability appears due to the interplay between the hardening nonlinearity of straightened curved beams used as the compliant suspensions and softening nonlinearity of the electrostatic force directed along the beams. Careful mapping of the parameters at the design stage resulted in reduced device sensitivity to fabrication tolerances and allowed to ensure bistability, necessary for the functionality of the sensor. The devices were fabricated from silicon on insulator substrates using deep reactive ion etching and bistability was demonstrated experimentally. Acceleration was emulated using electrostatic force and sensitivity of 0.173 V/g was registered in experiments. Good agreement between the experimental results and the model predictions was observed.