  An accurate estimate of the ferroelectric polarization in
ferroelectric-dielectric stacks is important from a materials science
perspective, and it is also crucial for the development of ferroelectric based
electron devices. This paper revisits the theory and application of the PUND
technique in Metal-Ferroelectric-Dielectric-Metal (MFDM) structures by using
analytical derivations and numerical simulations. In an MFDM structure the
results of the PUND technique may largely differ from the polarization actually
switched in the stack, which in turn is different from the remnant polarization
of the underlying ferroelectric. The main hindrances that prevent PUND
measurements from providing a good estimate of the polarization switching in
MFDM stacks are thus discussed. The inspection of the involved physical
quantities, not always accessible in experiments, provides a useful insight
about the main sources of the errors in the PUND technique, and clarifies the
delicate interplay between the depolarization field and the charge injection
and trapping in MFDM stacks with a thin dielectric layer.
