Ferroelectricity of as-deposited HZO fabricated by plasma-enhanced atomic layer deposition at 300 °C by inserting TiO₂ interlayers

We report the observation of ferroelectricity in hafnium-zirconium-oxide thin films in the as-deposited state, namely, after deposition at a low temperature of 300 °C without post-metallization annealing. The Hf_0.5Zr_0.5O₂ (HZO) thin film was interposed between two TiO₂ interlayers, and all films were produced by plasma enhanced atomic layer deposition and integrated into a TiN-based metal-insulator-metal capacitor. The ferroelectric nature of the as-deposited HZO film was evaluated by a polarization-voltage hysteresis loop, and a 2P_r value of ∼7.4 μC/cm² was achieved. Grazing incidence x-ray diffraction measurements and atomic-resolution scanning transmission electron microscopy characterization revealed the co-existence of fully crystallized polar orthorhombic and monoclinic phases of the dielectric in the as-deposited sample. We concluded that the nucleation and growth of the crystalline polar non-centrosymmetric orthorhombic phases in the 10 nm HZO thin film were prompted by the available energy from the plasma and the tensile lattice mismatch strain provided by the TiO₂ interlayer.