Ferroelectric La-doped ZrO${}_2$/Hf${}_x$Zr${}_{1-x}$O${}_2$ bilayer stacks with enhanced endurance

Hafnium zirconate (HZO) is investigated in metal-ferroelectric-metal capacitors as a function of Hf/(Hf+Zr) atomic ratio, the presence of a thin ZrO${}_2$ seed layer, and/or by doping HZO with La${}^{3+}$. It is demonstrated that a longer endurance is achieved with Hf-rich HZO by introducing a ZrO${}_2$ seed layer. The endurance is further improved by introducing La${}^{3+}$ in the Hf-rich HZO layer of the bilayer stack, which offers a higher 2P${}_r$ in the pristine state compared with a stoichiometric HZO doped with the same amount of La${}^{3+}$. Both ZrO${}_2$ underlayer and La${}^{3+}$ doping of HZO are shown to play a decisive role in promoting the formation of an orthorhombic and tetragonal phase at the expense of a detrimental monoclinic phase. (© 2021 Wiley-VCH GmbH)