Polarization switching and stability of nano-domains in Pb(Zr,Ti)O3 thin films using atomic force microscope (AFM)

Abstract

The bit formation using atomic force microscopy (AFM) was studied on 270 nm thick ＜111＞ preferentially oriented $Pb(Zr_{0.4}Ti_{0.6})O_3$ (PZT) films prepared by sol-gel process. To minimize the cantilever-sample capacitive force 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 in our film. The retention loss characteristics of polarized nano-size domains were measured on 150 nm thick ＜111＞ preferentially oriented $Pb(Zr_{0.4}Ti_{0.6})O_3$ (PZT) films grown by chemical solution deposition. The experiment was performed with high-aspect ratio tip for minimization of cantilever-sample capacitive force interaction. In order to examine the dependence of retention loss characteristics on domain structure, three different pulses (1, 3 and 5 ms pulse widths) were applied to form three kinds of domain configurations (ring, egg and dot structure). The sample was heat-treated at six temperatures (100, 130, 160, 190, 220 and 250℃) for a constant period (30 min.) and rapidly cooled down to room temperature before the measurement. The retention loss phenomena of the bit arrays were characterized by measuring the number, dimension, areal color density and average amplitude change of the remaining data bits. The areal color density change was explained from the relationship between the thermodynamics and kinetics. In addition, the average amplitude change was understood from the relationship between the portion of domain boundary an...