Improvement of Ferroelectric Properties in Hf 0.5 Zr 0.5 O 2 Capacitors Using Laminated ITO Electrodes

Fluorite-based HfO 2 ferroelectrics have attracted considerable interest because of their excellent compatibility with Si-based semiconductor technology; however, reliability issues have been encountered in practical applications. One is the wake-up effect: the electric field ( E ) cycling of the polarization– E ( P – E ) measurement is required until the remanent polarization ( P r ) is maximized. In this study, we demonstrated a remarkable improvement in the ferroelectric properties of Hf 0.5 Zr 0.5 O 2 (HZO) polycrystalline capacitors using laminated indium-tin-oxide (ITO) electrodes. An all-oxide ITO/HZO/ITO capacitor requires a considerable number of E cycling, i.e., a wake-up process, to maximize P r, which remains relatively small ( ∼ 12 μC/cm 2 ). By substituting the ITO top and bottom electrodes with laminated electrodes consisting of ITO (10 or 15 nm) and thin GaO x (2 nm), the wake-up effect was dramatically suppressed, and P r increased to ∼21 μC/cm 2 . Structural characterization revealed that the insertion of a thin GaO x layer between the ITO layers stabilized the metastable polymorph of ITO, i.e., the Rh 2 O 3 (II)-type orthorhombic (o) structure. In this laminated-electrode-based capacitor, the grain size of the HZO layer was much larger than that of the ITO/HZO/ITO capacitor, and the HZO layer was highly crystalline. This originates from the epitaxial-like growth of HZO with o-ITO in a pseudocoherent manner or via higher-order lattice matching. These results demonstrate an effective approach for improving the ferroelectric properties of HfO 2 -based capacitors.