Tailoring of Ferroelectric Coercive Field and Polarization With Ferroelectric and Antiferroelectric HfxZr1–xO2 Bilayer Structure

In this letter, the advantages of an antiferroelectric (AFE) and ferroelectric (FE) bilayer stack made of Hf_xZr $_{{1}-{\text {x}}}$ O₂(HZO) with different compositions were reported. Compared to the monolayer ferroelectric control sample, Mo/FE/Mo, the Mo/FE/AFE/Mo, and Mo/AFE/FE/Mo stacks exhibited a significant decrease in the coercive field (E $_{\text {c}}\text {)}$ . A higher dielectric constant of AFE increased the voltage distribution across the FE layer in the bilayer HZO structure, leading to a decrease in E_c. Furthermore, the capacitor with Mo/AFE/FE/Mo exhibited 28% higher polarization, P_r (2P $_{\text {r}} \,\, = \,\, 45.9~\mu $ C/cm $^{{2}}\text {)}$ , than the control sample, while this significant increase of P_r was not observed in the capacitor with Mo/FE/AFE/Mo. Electrical measurements of the capacitors with FE and AFE having various thicknesses showed that the dielectric constants and phase composition depend on the deposition sequence. A higher orthogonal phase ratio was achieved in the Mo/AFE/FE/Mo stack compared to the Mo/FE/AFE/Mo stack, resulting in higher polarization. Furthermore, bilayer capacitors with Mo/AFE/FE/Mo showed more robust long time reliability, such as endurance and retention.