A Janovec-Kay-Dunn-Like Behavior at Thickness Scaling in Ultra-Thin Antiferroelectric ZrO2 Films

Originally based on phenomenological observations, the Janovec-Kay-Dunn (JKD) scaling law has been historically used to describe the dependence of the ferroelectric coercive fields (E-c) on a critical length scale of the material, wherein the film thickness (t) is considered the length scale, and E-c proportional to t(-2/3). Here, for the first time, a JKD-type scaling behavior is reported in an antiferroelectric material, using the ultra-thin films of prototypical flourite-structure binary oxide, zirconia. In these films, a decrease in the ZrO2 layer thickness from 20 nm to 5.4 nm leads to an increase in critical fields for both nonpolar-to-polar (E-a), and polar-to-nonpolar (E-f) transitions, accompanied by a decrease in the average crystallite size, and an increase in the tetragonal distortion of the non-polar P4(2)/nmc ground state structure. Notably, the -2/3 power law as in the JKD law holds when average crystallite size (d), measured from glancing-incident X-ray diffraction, is considered as the critical length scale-i.e., E-a, E-f proportional to d(-2/3). First principles calculations suggest that the increase of tetragonality in thinner films contributes to an increase of the energy barrier for the transition from the non-polar tetragonal ground state to the field-induced polar orthorhombic phase, and in turn, an increase in E-a critical fields. These results suggest a de-stabilization of the ferroelectric phase with a decreasing thickness in antiferroelectric ZrO2, which is contrary to the observations in its fluorite-structure ferroelectric counterparts. With the recent interests in utilizing antiferroelectricity for advanced semiconductor applications, our fundamental exposition of the thickness dependence of functional responses therein can accelerate the development of miniaturized, antiferroelectric electronic memory elements for the complementary metal-oxide-semiconductor based high-volume manufacturing platforms.