Multiaxial resonant MEMS force sensor

Abstract

Miniaturized force sensors are indispensable components in various applications such as atomic force microscopes. In most cases the sensor is sensitive only to a single component at the force vector. For a complete characterisation of the actual load state all three components are required and this in combination with the three torque components (six-axis force/torque sensor). We report on a sensor to measure two components of the force vector and three components of the torques simultaneously using a resonant vibrating cross-shaped bar. The sensor is manufactured on an SOI wafer with standard Si-technology. The sensing structures are excited by Lorentz forces and detuned by the mechanical stress due to the applied force and torque. Currently, the shifts of the resonant frequencies are measured with a scanning laser vibrometer. To be able to compensate the influence of temperature additional Pt-termistors on the surface of the structure measure the actual temperature. Furthermore, the sensing structure is suspended to the sensor frame with compliant structures to reduce the temperature interferences. To investigate the effect of these substructures three different types are compared. With the multiaxial MEMS force sensor we achieved a sensitivity of almost 10 pN Hz−1.