Greatly enhanced fatigue resistance in Hf0.5Zr0.5O2/La0.7

Superlattices composed of ${\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}{\mathrm{O}}_{2}/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{Mn}\mathrm{O}}_{3}$ (HZO/LSMO), with nominally 10-nm-thick HZO and 1-nm-thick LSMO in a period, were deposited epitaxially on (110)-oriented $({\mathrm{La}}_{0.3}{\mathrm{Sr}}_{0.7})({\mathrm{Al}}_{0.65}{\mathrm{Ta}}_{0.35}){\mathrm{O}}_{3}$ (LSAT) substrates with thick LSMO electrodes. These 1-nm-thick LSMO spacer layers interrupt the growth of HZO grains, keeping the superlattice free from a paraelectric monoclinic phase. This makes it possible to achieve a total superlattice thickness above 50 nm in the pure ferroelectric orthorhombic phase. The strain gradient due to the strain relaxation in thick superlattices induces a rhombohedral distortion with the help of the flexoelectric field. The distorted structure is more stable than the metastable orthorhombic ferroelectric phase, making it more resistant to ferroelectric fatigue. The $(\mathrm{HZO}/\mathrm{LSMO}{)}_{5}$ superlattice exhibits a large remanent polarization of about 19.3 \textmu{}C/${\mathrm{cm}}^{2}$ and a greatly enhanced fatigue resistance, by keeping more than 90% of its polarization after ${10}^{9}$ bipolar switching cycles. Our results provide additional opportunities for the design and optimization of ${\mathrm{Hf}\mathrm{O}}_{2}$-based ferroelectric materials to optimize the structure and properties for integrated ferroelectric applications.