Ferroelectric La-Doped ZrO2/HfxZr1-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 ZrO2 seed layer, and/or by doping HZO with La3+. It is demonstrated that a longer endurance is achieved with Hf-rich HZO by introducing a ZrO2 seed layer. The endurance is further improved by introducing La3+ 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 La3+. Both ZrO2 underlayer and La3+ 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.