We investigated the time-dependent domain wall motion of epitaxial PbZr0.2Ti0.8O3 capacitors 100 nm-thick using modified piezoresponse force microscopy (PFM). We obtained successive domain evolution images reliably by combining the PFM with switching
current measurements. We observed that domain wall speed (v) decreases with increases in domain size. We also observed that the average value of v, obtained under applied electric field (Eapp),showed creep behavior: i.e. <v> ~ exp(-E0/Eapp)^$mu$ with an exponent $mu$ of 0.9 $pm$ 0.1 and an activation field E0 of about 700 kV/cm.
We investigated the time-dependent polarization switching behaviors of (111)-preferred polycrystalline Pb(ZrxTi1-x)O3 thin films with various Zr concentrations. We could explain all the polarization switching behaviors well by assuming Lorentzian dis
tributions in the logarithmic polarization switching time [Refer to J. Y. Jo et al., Phys. Rev. Lett. (in press)]. Based on this analysis, we found that the Zr ion-substitution for Ti ions would induce broad distributions in the local field due to defect dipoles, which makes the ferroelectric domain switching occur more easily.
We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors under a modified piezoresponse force microscope. We obtained domain evolution images during polarization switching process and observed that domain nucleation occurs at par
ticular sites. This inhomogeneous nucleation process should play an important role in an early stage of switching and under a high electric field. We found that the number of nuclei is linearly proportional to log(switching time), suggesting a broad distribution of activation energies for nucleation. The nucleation sites for a positive bias differ from those for a negative bias, indicating that most nucleation sites are located at ferroelectric/electrode interfaces.
We investigated domain kinetics by measuring the polarization switching behaviors of polycrystalline Pb(Zr,Ti)O$_{3}$ films, which are widely used in ferroelectric memory devices. Their switching behaviors at various electric fields and temperatures
could be explained by assuming the Lorentzian distribution of domain switching times. We viewed the switching process under an electric field as a motion of the ferroelectric domain through a random medium, and we showed that the local field variation due to dipole defects at domain pinning sites could explain the intriguing distribution.
