Simultaneously achieving high-κ and strong ferroelectricity in Hf0.5Zr0.5O2 thin film by structural stacking design

Abstract

The superior dielectric and ferroelectric properties of HfO₂-based thin films, coupled with excellent silicon compatibility, position them as highly attractive candidates for dynamic and ferroelectric random-access memories (DRAM and FeRAM). However, simultaneously achieving high dielectric constant (κ) and strong ferroelectricity in HfO₂-based films presents a challenge, as high-κ and ferroelectricity are associated with the tetragonal and orthorhombic phases, respectively. In this study, we report both the good ferroelectric and dielectric properties obtained in W/Hf_0.5Zr_0.5O₂ (HZO ∼6.5 nm)/W with morphotropic phase boundary structure by optimizing stacking sequence of HfO₂ and ZrO₂ sublayers. Notably, by alternating stacking of 1-cycle HfO₂ with 1-cycle ZrO₂ sublayers ((1–HfO₂)/(1–ZrO₂)), high-κ (>50) and large polarization (2P_r >40 μC/cm², after wake-up) can be achieved. Besides, the (1–HfO₂)/(1–ZrO₂) stacking configuration presents better thermal stability compared to other stacking sequences. Furthermore, the incorporation of an Al₂O₃ layer leads to a low leakage current density (<10^–7 A/cm² at 0.65 V) and high dielectric endurance over 10¹³ cycles (operating voltage ∼0.5 V). A low equivalent oxide thickness (EOT ∼0.53 nm) and considerable polarization with low leakage are simultaneously achieved. These results highlight the potential of HfO₂-based films with optimized structural stacking as a trade-off approach for integrating DRAM and FeRAM on one-chip.