Physikalisch-Technische Bundesanstalt

The production and scanning of smallest forces into the pico Newton range is required in various fields of fundamental and applied research. For these requirements, a transducer based on a microelectromechanical system (MEMS) was developed. With the aid of multiple-folded Si springs, its stiffness in the scanning direction is reduced. For the force scanning and feedback of the transducer, the in-plane displacement of the springs is capacitively measured with high resolution. The force transducer is characterized by a simple structure, a reliable feedback strategy as well as an integrated electrostatic force generator. The latter delivers the desired balanced force in order to eliminate the potential nonlinearity in force scanning.

A prototype of the picoforce transducer was produced in Si microtechnology using deep reactive ion etching and bond contacting. It exhibits a very low stiffness in the scanning direction of 0.254 N/m and a resolution in force feedback of 50.8 pN (1 σ). With a pair of electrostatic comb actuators, the prototype can produce a maximum electrostatic force of 1.23 µN. Due to the special form of its scanning element, the picoforce transducer can find various applications, among other things as pico/nano force transfer standard, in the calibration of sensors for small forces, in the determination of the mechanical properties of micro/nano materials und in the investigation of the lateral force of scanning force microscopes.