Engineering\nof Ferroelectric HfO₂–ZrO₂ Nanolaminates

Abstract

In\nthis work, the ferroelectric properties of nanolaminates made of HfO₂ and ZrO₂ were studied as a function of the deposition\ntemperature and the individual HfO₂/ZrO₂ layer\nthickness before and after electrical field cycling. The ferroelectric\nresponse was found to depend on the structure of the nanolaminates\nbefore any postdeposition annealing treatment. After annealing with\na TiN cap, an “antiferroelectric-like” response was\nobtained from nanolaminates deposited in an amorphous state at a lower\ntemperature, whereas a ferroelectric response was obtained from nanolaminates\ndeposited at a higher temperature, where crystallites were detected\nin thick films before annealing. As the individual layer thicknesses\nwere decreased, an increased lattice distortion and a concurrent increase\nin remanent polarization were observed from the nanolaminates deposited\nat high temperatures. After field cycling, nanolaminates deposited\nat lower temperatures exhibited an antiferroelectric-like to ferroelectric transition, whereas those\ndeposited at higher temperatures exhibited a larger remanent polarization.\nFinally, we demonstrate that by leveraging the proper choice of process\nconditions and layer thickness, remanent polarizations exceeding those\nof the HfZrO₄ solid solution can be obtained.