The device description consists of the geometry and a special list of keywords necessary for describing the properties of the ferroelectric material. An overview of these keywords and their default values is given in Table 6.2.
The
geometry is stored in a separate file which is specified in the
Input section of the input deck. In order to enter a ferroelectric
material into the device, the command ferro = segname in
the Phys section has to be added. The ferroelectric
properties of the specified segment have to be declared in the
Solve section.
According to the implemented model, three parameters are necessary to
describe the hysteresis:
PsatFerro for the saturation polarization
,
ECoercFerro for the coercive field
,
ShapeFerro for the shape of the hysteresis. Using these parameters the
remanent polarization
and the parameter
are calculated.
If the material is anisotropic, the axes properties are specified with
the keyword
FerroHysteresisModel. It is used to toggle between the different shape functions.
If this keyword is set to 1 the is selected, if set to
2, the
shape function is selected.
The number of axes is specified with the keyword FerroAxesNumber. Default is
one.
The keyword
FerroAxisI = 0...1 specifies the first anisotropy axis. The
value entered is the cosinus of the angle to the x-axis, and default is zero.
FerroAxisII = 0...1 specifies the second axis.
The value entered is defined the same way as for the first axis.
The three parameters for the transient simulation are :
RelaxFerro, the time constant for the polarization
,
RelaxFerroEf, the time constant for the electric field
, and
RelaxFerroExp, the value of the nonlinear parameter
.
All of these keywords are set to zero by default.