Design and control of a MEMS nanopositioner with bulk piezoresistive sensors

A 2 degree of freedom microelectromechanical system (MEMS) nanopositioner is presented in this paper. The nanopositioner is fabricated using a standard silicon-on-insulator process. The device demonstrates a bidirectional displacement in two orthogonal directions. As the displacement sensing mechanism, bulk piezoresistivity of tilted clamped-guided beams is exploited. The characterization reveals more than 15 μm displacement range and an in-plane bandwidth of above 3.6 kHz in both axes. The piezoresistive sensors provide a bandwidth which is more than ten times larger than the stage's resonant frequency. To evaluate the sensor performance in closed-loop, an integral resonant controller together with an integral tracking controller are implemented where piezoresistive sensor outputs are used as measurement. The controlled nanopositioner is used for imaging in an atomic force microscope.