The Bit formation using atomic force microscopy (AFM) was studied on 270-nm-thick < 111 > preferentially oriented Pb(Zr0.4Ti0.6)O-3 (PZT) films prepared by the sol-gel process. To minimize the cantilever-sample capacitive farce interaction, the experiment was carried out at or near the sample edge. Bit formation was investigated by calculating the electric field in AFM-tip/PZT film/bottom electrode configuration. It was found both experimentally and theoretically that:the bit size is linearly dependent on the pulse voltage-and the logarithmic value of the pulse width, The linear dependence of the bit size on the logarithmic value of pulse width was explained from the relationship between the switching time and electric field. It was found that the minimum bit size of a fully penetrating domain equals the film thickness.