6.3.1 Memory Management

As already outlined, the current value of polarization does not only depend on the current value of the electric field, but also the entire history has to be considered. For the implemented models, the relevant information of the device history consists of the electric field strength and the polarization at the turning points of the applied electric field.

Whereas the electric field at the boundary can easily be extracted from the potential at the grid points, this is not possible for the polarization. Therefore, the memory management of MINIMOS-NT was expanded in two ways: First, the values of all polarization and electric field quantities, which cannot be recovered from the on-grid quantities of the previous operating point, are to be memorized ( $\vec{P},\vec{P}_\mathrm{turn},\vec{E}_\mathrm{turn})$. Second, at each of the boundaries a stack has to be set up which contains the entire information on the device history.

The occurrence of a turning point is detected by comparison of the current direction with the previous one. If the direction changes, the values of the previous operating point are pushed to the stack, following the principle of the Preisach hysteresis concept concerning memory wipe-out (Subsection 3.2.4). The value of the electric field is compared to its precursor on the stack, and if the new value is higher, the old value is removed from the stack.