Improvement of Ferroelectric Properties in Hf _0.5 Zr _0.5 O ₂ Capacitors Using Laminated ITO Electrodes

Fluorite-based HfO2 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 (Pr) is maximized. In this study, we demonstrated a remarkable improvement in the ferroelectric properties of Hf0.5Zr0.5O2 (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 Pr, which remains relatively small (∼12 μC/cm2). By substituting the ITO top and bottom electrodes with laminated electrodes consisting of ITO (10 or 15 nm) and thin GaOx (2 nm), the wake-up effect was dramatically suppressed, and Pr increased to ∼21 μC/cm2. Structural characterization revealed that the insertion of a thin GaOx layer between the ITO layers stabilized the metastable polymorph of ITO, i.e., the Rh2O3(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 HfO2-based capacitors.