Complex Internal Bias Fields in Ferroelectric Hafnium Oxide.

For the rather new hafnia- and zirconia-based ferroelectrics, a lot of questions are still unsettled. Among them is the electric field cycling behavior consisting of (1) wake-up, (2) fatigue, and (3) the recently discovered subcycling-induced split-up/merging effect of transient current peaks in a hysteresis measurement. In the present work, first-order reversal curves (FORCs) are applied to study the evolution of the switching and backswitching field distribution within the frame of the Preisach model for three different phenomena: (1) The pristine film contains two oppositely biased regions. These internal bias fields vanish during the wake-up cycling. (2) Fatigue as a decrease in the number of switchable domains is accompanied by a slight increase in the mean absolute value of the switching field. (3) The split-up effect is shown to also be related to local bias fields in a complex situation resulting from both the field cycling treatment and the measurement procedure. Moreover, the role of the wake-up phenomenon is discussed with respect to optimizing low-voltage operation conditions of ferroelectric memories toward reasonably high and stable remanent polarization and highest possible endurance.