Design and Control of a Three-Axis Serial-Kinematic High-Bandwidth Nanopositioner

Abstract

The development of a high-performance three-axis serial-kinematic nanopositioning stage is presented. The stage is designed for high-bandwidth applications that include video-rate scanning probe microscopy and high-throughput probe-based nanofabrication. Specifically, the positioner employs vertically stiff, double-hinged serial flexures for guiding the motion of the sample platform to minimize parasitic motion (runout) and off-axis effects compared to previous designs. Finite element analysis (FEA) predicts the dominant resonances along the fast ( x-axis) and slow ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -axis) scanning axes at 25.9 and 6.0 kHz, respectively. The measured dominant resonances of the prototype stage in the fast and slow scanning directions are 24.2 and 6.0 kHz, respectively, which are in good agreement with the FEA predictions. In the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -direction, the measured dominant resonance is approximately 70 kHz. The lateral and vertical positioning ranges are approximately 9 μm × 9 μm and 1 μm, respectively. Four approaches to control the lateral motion of the stage are evaluated for precision tracking at high-scan rates: (1) open-loop smooth inputs; (2) PID feedback; (3) discrete-time repetitive control implemented using field-programmable gate array (FPGA) hardware; and (4) model-based feed forward control. The stage is integrated with a commercial scan-by-probe atomic force microscope (AFM) and imaging and tracking results up to a line rate of 7 kHz are presented. At this line rate, 70 frames/s atomic force microscope video (100 × 100 pixels resolution) can be achieved.