Two-step polarization switching mediated by a nonpolar intermediate phase in Hf0.4Zr0.6O2 thin films.

The broken ferroelectric hysteresis loop achieved from a Hf0.4Zr0.6O2 film was interpreted based on the first order phase transition theory. The two-step polarization switching, which was expected from the theory, could be observed by dynamic pulse switching measurement. The variations in the interfacial capacitance values along with switching time and number of switching cycles could also be estimated from the pulse switching test. Being different from the one-step polarization switching in other ferroelectric films, two-step polarization switching produced two slanted plateau regions where the estimated interfacial capacitance values were different from each other. This could be understood based on the quantitative model of the two-step polarization switching with the involvement of an intermediate nonpolar phase. The Hf0.4Zr0.6O2 film was changed from antiferroelectric-like to ferroelectric-like with the increasing number of electric field cycles, which could be induced by the field driven phase change.