USING CAPACITIVE SENSORS FOR INSITU CALIBRATION OF DISPLACEMENTS IN A PIEZO-DRIVEN TRANSLATION STAGE OF AN STM

The uncertainty in the exact lateral position of the moving part relative to the frame is one of the technical problems in piezo-driven translation stages for submicron translations. This is mainly caused by non-linearities in the piezo actuators and thermal drift in the construction. The piezo voltages are therefore not appropriate as the reference for the absolute displacement. In this paper we show some non-ideal properties of a one-dimensional piezo-driven translation stage, which could be used in a scanning tunnelling microscope (STM), for instance. To eliminate the position uncertainty of the displacement, we have installed an independent calibration system which measures the displacement. We use a capacitive sensor system with a resolution in the picometre range. Using the sensor information, we are able to calibrate the stage displacements beforehand or correct the actual piezo voltages in a feedback loop during displacement. We obtain an absolute calibrated position determination and hysteresis-free linear displacements.