Direct observation of inversely polarized frozen nanodomains in fatigued ferroelectric memory capacitors

The direct observation of blocked polarization domains at the electrode-ferroelectric interface of electrically fatigued ferroelectric films is reported. Blocked nanodomains are believed to be the origin of polarization fatigue in ferroelectric nonvolatile memories but have not been directly observed so far due to the required upper metal electrode which impedes the direct access to the surface of the ferroelectric film. This problem has been solved by using low temperature melting metal as removable top electrode. After fatigue and subsequent top electrode removal it was possible to observe the polarization state of the fatigued capacitor and its depth profile by means of detection of the local piezoelectric activity with a conductive atomic force microscope tip. Blocked polarization domains with opposite polarization compared to the film body could be directly observed at the upper ferroelectrics surface. (C) 2003 American Institute of Physics.