Hf_0.5Zr_0.5O₂ (HZO) ferroelectric thin films have gained significant attention for the development of next-generation ferroelectric memories by complementary-metal-oxide semiconductor (CMOS) back-end-of-line (BEOL) processing, due to their relatively low crystallization temperature. However, it remains challenging to achieve excellent ferroelectric properties with post deposition annealing (PDA) process at a BEOL compatible temperature. Along these lines, in this work, it is demonstrated that the ferroelectricity of 15 nm thick HZO thin film prepared by PDA process at 400 °C can be improved to varying degrees, via depositing 2 nm thick dielectric layers of Al₂O₃, HfO₂, or ZrO₂ at either the bottom or the top of the film. Notably, the HZO thin film with the top-Al₂O₃ layer exhibits remarkable ferroelectric properties, which are independent of the thickness of HZO. The 6 nm thick HZO thin film shows a total remanent polarization (2P_r) of 31 μC/cm² under an operating voltage of 2.5 V. These results represent a significant advancement in the fabrication of high-performance, BEOL compatible ferroelectric memories, as compared to previously reported state-of-the-art works.

Multilevel ferroelectric field−effect transistors (FeFETs) integrated with HfO₂−based ferroelectric thin films demonstrate tremendous potential in high−speed massive data storage and neuromorphic computing applications. However, few works have focused on the stability of the multiple memory states in the HfO₂−based FeFETs. Here we firstly report the write/read disturb effects on the multiple memory states in the Hf_0.5Zr_0.5O₂ (HZO)−based FeFETs. The multiple memory states in HZO−based FeFETs do not show obvious degradation with the write and read disturb cycles. Moreover, the retention characteristics of the intermediate memory states in HZO−based FeFETs with unsaturated ferroelectric polarizations are better than that of the memory state with saturated ferroelectric polarization. Through the deep analysis of the operation principle of in HZO−based FeFETs, we speculate that the better retention properties of intermediate memory states are determined by the less ferroelectric polarization degradation and the weaker ferroelectric polarization shielding. The experimental and theoretical evidences confirm that the long−term stability of the intermediate memory states in HZO−based FeFETs are as robust as that of the saturated memory state, laying a solid foundation for their practical applications.