A key question for the simulation model is whether it is justified to ignore the existence of domains and to treat the material as a continuum. Indeed, experimental data for PZT directly deposited on Ti/Pt electrodes show a dependence of ferroelectric properties on the thickness of the film, thus questioning this approach. These difficulties were solved by the assumption of a non-ferroelectric blocking layer (Fig. 4.12) at the interface of the contact electrodes.
Thus good correspondence of the measured data to the continuum
approach was obtained [LDTvV94]. These calculations were carried
out using a one-dimensional continuum model. The decisive parameter
for the blocking layer is the ratio between its relative dielectric
constant
and its thickness
. The
reported, specimen dependent, values of
are 20-30
.
Later experiments with
electrodes
immediately matched the expected predictions of linear scaling of
field properties [CPW97], thus giving further evidence that
the model is appropriate.