High resolution study of domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 ferroelectric thin film capacitors

Abstract

The domain nucleation and growth during polarization switching in Pb(Zr,Ti)O3 (PZT) ferroelectric thin film capacitors with Pt top (TE) and bottom electrodes (BE) were studied by means of atomic force microscopy (AFM). The experimental configuration used in this study differs from that conventionally used (AFM tip/PZT/BE) where the AFM tip acts as a positionable TE. A small ac voltage was applied between the electrodes with a step by step increasing dc bias voltage. The induced piezoelectric vibration was detected by the AFM tip, its amplitude and phase determined with the lock-in amplifier. The phase difference between the applied ac voltage and the piezoelectric signal as a function of the x-y position was nearly locked at 0 or 180, representing film regions with parallel (in-phase) and antiparallel (antiphase) polarization direction, respectively. The polarization reversal was induced by application of a step by step increasing dc bias field opposite to the polarization of the prepoled sample. At each bias step 10 μm×10 μm images of the amplitude and the phase were collected. By approaching the coercive field (Ec), a rapid decrease of the amplitude with a small change in phase was observed, first in preferential sites for reversed nucleation, then over the whole studied area. The first regions with reversed polarization were observed at about 3.2 MV/m and the switching was completed at 5.5 MV/m. The results were interpreted using both the forward and the sideways domain growth models that are named by their rate-limiting kinetics. It was concluded that under the assumption of a sufficient resolution of domain imaging in our study, the forward domain growth being the rate limiting mechanism prevails in our PZT thin film.