Ferroelectricity of Hf_0.5Zr_0.5O₂ thin films grown by atomic layer deposition on epitaxial TiN bottom electrodes

In this study, the effects of the epitaxial TiN bottom electrode on the crystallinity and ferroelectricity of Hf_0.5Zr_0.5O₂ (HZO) thin films were investigated. HZO thin films were deposited using atomic layer deposition on epitaxial TiN(100) on MgO(100), epitaxial TiN(111) on Al₂O₃(0001), and polycrystalline TiN on Si(100) for comparison. The HZO thin films on epitaxial TiN(100) exhibited the largest remanent polarization of ∼26 μC/cm², with the largest orthorhombic phase fraction. Conversely, the HZO thin film on polycrystalline TiN showed the smallest remanent polarization ∼19 μC/cm², with the smallest orthorhombic phase fraction. High-resolution transmission electron microscopy analysis confirmed the dominance of the orthorhombic phase in the HZO thin film on epitaxial TiN(100). Reliability tests showed that the HZO thin films on epitaxial TiN (100) exhibited superior retention with a smaller wake-up effect compared to those of the HZO thin films on polycrystalline TiN but they displayed inferior cycling endurance characteristics.