Evolution of pronounced ferroelectricity in Hf0.5Zr0.5O2 thin films scaled down to 3 nm

Abstract

The thickness scaling of the ferroelectric (FE) hafnium zirconium oxide (HZO) down to sub-10 nm is essential in non-volatile memory devices. In this study, high remnant polarization (P_r), low thermal budget, low operation voltage, and high endurance are demonstrated in the FE HZO thin films with thickness shrinkage from 10 to 3 nm. Due to the in-plane tensile stress induced by the TiN capping layer and the initial island growth on the platinum bottom electrode, record-high P_r ∼24.8 μC cm⁻² is realized in the 6 nm HZO layer. Good ferroelectricity with P_r ∼10.8 μC cm⁻² and low saturation voltage (∼0.7 V) is also achieved in the 3 nm HZO thin film. The wake-up effect is insignificant as the HZO thickness is greater than 5 nm, while an obvious wake-up effect is observed in sub-5 nm HZO thin films. This result can be ascribed to the increasing stability of the tetragonal phase with a decrease of the HZO thickness as supported by the dielectric constant measurement. The dielectric breakdown strength of the HZO layers was evaluated by the time-zero dielectric breakdown test. The dielectric breakdown strength increases rapidly with a decrease of the HZO thickness, which leads to a significant endurance improvement with ∼10¹¹ electric field cycling without breakdown in the 3 nm HZO thin film. The favorable FE properties demonstrated in the sub-5 nm HZO thin films provide a promising approach in future FE non-volatile memory applications.