Direct observation of region by region suppression of the switchable polarization (fatigue) in Pb(Zr,Ti)O-3 thin film capacitors with Pt electrodes

Abstract

The size, shape, and polarization orientation of fatigued areas formed during the suppression of the switchable polarization (P-r(s)) (fatigue) in Ft-FZT-Pt ferroelectric capacitors (FECAPs), were observed by means of atomic force microscopy and by imaging the phase of the piezoelectric vibration induced by a low ac field applied between the top and bottom electrodes. In the virgin state (FECAP as prepared), the pattern of the polarization domains with opposite orientation was randomly distributed with typical sizes of 1-3 mu m. The application of a de field larger than the coercive field (E-c) enabled to fully orient the polarization of the regions in either directions. During the initial fatigue (<35% of suppressed P-r(s)), polarized regions with frozen orientation and size ranging between 100 nm and 1 mu m became visible. In the fatigued state (>65% of suppressed P-r(s)), two main configurations of the frozen polarization domains were distinguished. One was characterized by a strong preferential direction (top to bottom electrode) and the other by randomly distributed regions of opposite oriented frozen polarization. The degrees of fatigue obtained by analyzing the vibration phase images are in good agreement with those obtained by standard polarization measurements. It is concluded that the Ps. suppression (fatigue) is due to "region by region" or "grain by grain" freezing of P-r(s) and that the frozen P-r(s) can have a preferential orientation. (C) 1998 American Institute of Physics.