FIGURE 2-8 Left: A piezoelectric cylinder has electrodes on the inside and outside so that the potential goes through the wall of the ceramic. When activated the cylinder elongates. Right: A piezoelectric bimorph has two sheet of piezoelectric material bonded together. The end of the bimorph expands in a parabolic motion when activated.

FIGURE 2-9 Top: PZT materials have hysteresis. When a voltage ramp is placed on the ceramic, the motion is nonlinear. Bottom: Creep occurs when a voltage pulse on a PZT causes initial motion followed by drift.

Ideally, the piezoelectric ceramics would expand and contract in direct proportion to the driving voltage. However, piezoelectric materials have two primary non-ideal behaviors, hysteresis and creep. Hysteresis, derived from the word history, causes the ceramic to maintain the shape that it was in. As the ceramic is expanding, there is a negative shaped non-linearity, and as the material is contracting, there is a positive shaped non-linearity. Creep occurs when the ceramic is subjected to a sudden impulse such as a voltage step function. These non-ideal behaviors must be corrected or they cause distortions in AFM images.