Ferroelectric La-Doped ZrO₂/Hf_xZr_1-xO₂ 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.