Piezoelectric Scanners: Hysteresis and Aging
16
Scanning Probe Microscope Training Notebook
Rev. F
8.0
Piezoelectric Scanners: Hysteresis and Aging
8.1 Hysteresis
Because of differences in the material properties and dimensions of each piezoelectric element,
each scanner responds differently to an applied voltage. This response is conveniently measured in
terms of sensitivity, a ratio of piezo movement-to-piezo voltage, i.e., how far the piezo extends or
contracts per applied volt.
Sensitivity is not a linear relationship with respect to scan size. Because piezo scanners exhibit
more sensitivity (i.e., more movement per volt) at the end of a scan line than at the beginning, the
relationship of movement vs. applied voltage is nonlinear. This causes the forward and reverse scan
directions to behave differently and display hysteresis between the two scan directions.
Figure 8.1a
Effect of Nonlinearity and Hystersis
The effect of nonlinearity and hysteresis can be seen from the curve above (see
piezo extends and retracts throughout its full range, it moves less per applied volt at the beginning
of the extension than near the end. The same is true when the piezo is retracting - the piezo moves
less per applied volt at the beginning of its extension than near the end.
Nonlinearity and hysteresis can cause feature distortion in SPM images if not properly corrected.
Examples of these effects on AFM images are shown below with the DI-supplied 10 µm pitch
calibration grating. The depth of each square is 200nm. Please refer to the standard for step height
information.
