Optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope

- A nano-positioning stage for a vertical probe microscope is optimised.
- Optimisation was achieved through a combination of modelling and prototype testing.
- A 12-fold increase in resonant frequency was achieved (from 500 to 6000 Hz).
- Out-of-plane distortions were reduced to from 0.3 to less than 0.05 μm.
- The optimised stage will enable much higher speeds of scanning for the microscope.

This paper describes the optimisation of a nano-positioning stage for a Transverse Dynamic Force Microscope (TDFM). The nano-precision stage is required to move a specimen dish within a horizontal region of 1 μm × 1 μm and with a resolution of 0.3 nm. The design objective was to maximise positional accuracy during high speed actuation. This was achieved by minimising out-of-plane distortions and vibrations during actuation. Optimal performance was achieved through maximising out-of-plane stiffness through shape and material selection as well optimisation of the anchoring system. Several shape parameters were optimised including the shape of flexural beams and the shape of the dish holder. Physical prototype testing was an essential part of the design process to confirm the accuracy of modelling and also to reveal issues with manufacturing tolerances. An overall resonant frequency of 6 kHz was achieved allowing for a closed loop-control frequency of 1.73 kHz for precise horizontal motion control. This resonance represented a 12-fold increase from the original 500 Hz of a commercially available positioning stage. Experimental maximum out-of-plane distortions below the first resonance frequency were reduced from 0.3 μm for the first prototype to less than 0.05 μm for the final practical prototype.