Mechanisms of imprint effect on ferroelectric thin films

We have developed a single/double layer model to explain horizontal shifting of measured D-E hysteresis loops (imprint) for ferroelectric thin films. Such phenomenon can be explained by considering three mechanisms or their multiple effects: (1) stress induced by film/electrode lattice mismatch or clamping, (2) domain pinning induced by, e.g., oxygen vacancies, or (3) degradation of ferroelectric properties in film/electrode surface layers. First, it is found that hysteresis loops under the influence of stress exhibit large horizontal shifts with magnitudes comparable to those observed in experiments. Second, a pseudo-non-switching layer with a large coercive field is assumed to be present at the film/electrode interface in an otherwise homogeneous ferroelectric thin film, and in this case our simulation also shows a large imprint effect. Third, it is also found that time-dependent space-charge-limited conduction is likely to be one origin for the occurrence of imprint.