Optimizing Monolayer Ferroelectric ZrO₂ on Si (001)

A single atomic layer of ZrO₂ grown directly on an abrupt Si (001) surface shows ferroelectric switching behavior.^[1] Being at the ultimate thickness limit of a monolayer (ML), this system has the potential to aggressively scale down device size. Motivated by density functional theory (DFT) calculations that attribute the polarization switching to displacements of Zr-O dipoles, we aim to control the magnitude of capacitance – voltage (C-V) hysteresis by controlling the density of Zr-O dipoles in the ML ZrO₂ film. We report that the Zr-O dipole density in the ML ZrO₂ can be controlled by varying film annealing conditions and characterized using x-ray photoelectron spectroscopy (XPS) measurements of Zr 3d core level energies. Results show that the Zr⁴⁺ XPS relative intensity can vary from about 30% to 90% depending on the film annealing conditions. Using C-V measurements, we show that the magnitude of the hysteresis is proportional to the density of Zr-O dipoles as characterized by XPS, and thus can be optimized by varying the annealing conditions.<br/> <br/><b>Reference </b><br/>[1] M. Dogan, S. Fernandez-Pena, L. Kornblum, Y. Jia, D. P. Kumah, J. W. Reiner, Z. Krivokapic, A. M. Kolpak, S. Ismail-Beigi, C. H. Ahn, F. J. Walker, Nano Lett. <b><i>18</i></b> (1), 241-246 (2018); https://doi.org/10.1021/acs.nanolett.7b03988