Depolarization as Driving Force in Antiferroelectric Hafnia and Ferroelectric Wake-Up

Abstract

Antiferroelectricity and wake-up observed in thin hafnium-oxide-based ferroelectrics are examined from the viewpoint of a macroscopic, quantitative model incorporating depolarization effects. Depolarization fields arising from finite screening, a nonferroelectric interface, and a ferroelectric/paraelectric phase mixture are shown to directly impact the switching properties and shape of ferroelectric hysteresis. Charge injection and trapping are used to demonstrate how the progressive stressing of a ferroelectric dead layer results in improved switching with electric-field cycling. The description of ferroelectric hysteresis is applied to HfO2-based ferroelectrics where the longstanding debate concerning wake-up cycling and antiferroelectric properties can be shown to be driven by depolarization mechanisms. The calculated hystereses combine quantitative accuracy, simplicity, and compatibility to multiple microscopic interpretations that show depolarization fields can be the driving force of a field-induced first-order phase transition underlying antiferroelectric behavior.

Wake‐Up Mechanisms in Ferroelectric Lanthanum‐Doped Hf0.5Zr0.5O2 Thin Films

“…Accordingly, first a slow and later a faster wake-up process occurs. [24] These two regions are clearly visible also for measurements on La-doped Hf 0.5 Zr 0.5 O 2 samples at RT ( Figure 3A). As a reduced amount of the tetragonal phase is assumed for liquid nitrogen temperature, here the wake-up would be reduced.…”

“…[ 16 ] From both effects, Lomenzo et al proposed a possible wake‐up scenario with two different cycling phases. [ 24,25 ] In the initial phase, charge injection and charge redistribution within the dielectric/metal interface layer cause a depinning of domains and shielding of depolarization fields. In the second phase, closely related to the reduction of the interface resistivity, a partial breakdown of the interface layer is proposed.…”

“…[24,25] Details on the effect of depolarization fields on the hysteresis loop and field-cycling can be found in ref. [24]. As mentioned earlier, so far, the depinching of hysteresis loop was reported with decreasing ambient temperature or field-cycling of the pristine films.…”

“…Apart from the nonpolar‐to‐polar phase transition, there are several other mechanisms proposed to explain the changes observed with field‐cycling in the wake‐up phase such as the depinning of domains, [ 22 ] a polarization orientation change, [ 23 ] or cycling‐induced changes in the depolarization field. [ 24,25 ] During depinning of domains, charges at domain walls and grain boundaries are redistributed during field‐cycling which can enhance switching performance of these domains or grains. As reported by Shimizu et al, [ 19 ] an in‐plane‐to‐out‐of‐plane polarization change can be found in epitaxial grown Y:HfO 2 films, but again orientation changes seem to be small (<5%) compared with the polarization change.…”

“…Both effects result in a P r increase. [ 24,25 ] Details on the effect of depolarization fields on the hysteresis loop and field‐cycling can be found in ref. [24].…”