Engineering of Ferroelectric HfO2–ZrO2 Nanolaminates
journal contributionposted on 24.03.2017, 00:00 by Stephen L. Weeks, Ashish Pal, Vijay K. Narasimhan, Karl A. Littau, Tony Chiang
In this work, the ferroelectric properties of nanolaminates made of HfO2 and ZrO2 were studied as a function of the deposition temperature and the individual HfO2/ZrO2 layer thickness before and after electrical field cycling. The ferroelectric response was found to depend on the structure of the nanolaminates before any postdeposition annealing treatment. After annealing with a TiN cap, an “antiferroelectric-like” response was obtained from nanolaminates deposited in an amorphous state at a lower temperature, whereas a ferroelectric response was obtained from nanolaminates deposited at a higher temperature, where crystallites were detected in thick films before annealing. As the individual layer thicknesses were decreased, an increased lattice distortion and a concurrent increase in remanent polarization were observed from the nanolaminates deposited at high temperatures. After field cycling, nanolaminates deposited at lower temperatures exhibited an antiferroelectric-like to ferroelectric transition, whereas those deposited at higher temperatures exhibited a larger remanent polarization. Finally, we demonstrate that by leveraging the proper choice of process conditions and layer thickness, remanent polarizations exceeding those of the HfZrO4 solid solution can be obtained.