An SOI-MEMS Piezoelectric Torsional Stage With Bulk Piezoresistive Sensors

This paper presents a micro-electromechanical stage for out-of-plane positioning of microcantilevers designed for atomic force microscopes. The stage produces an out-of-plane displacement using a torsional mechanism that exploits piezoelectric clamped-guided beams as actuators. To measure the torsional displacement of the stage, novel differential piezoresistive sensors are implemented. These sensors feature clamped-guided beams that exploit the bulk piezoresistivity of silicon. Using this sensing concept eliminates the requirement to fabricate highly doped regions on the flexures. An analytical model is provided that describes the sensor's linearity. The sensor, the microcantilevers, and the mechanical features of the stage are experimentally characterized. The first resonance frequency of the stage is located at 7.8 kHz, and a static out-of-plane displacement of more than 1.2 mu m is obtained. In addition, the piezoresistive sensor captures the dynamics of the stage within a bandwidth of 13 kHz with a 1 sigma -resolution of 3 nm.