Low Voltage High Polarization by Optimizing Scavenged WN_x Interfacial Capping Layer at the Ru/Hf_xZr_1-xO₂ Interface and Evidence of Fatigue Mechanism

In this study, the double remnant polarization (2P_r) is enhanced from ≈2 to 25 µC cm⁻² at a low applied voltage of ±2 V (or from 10 to 35 µC cm⁻² at a voltage of ±4 V) by decreasing the WN_x interfacial capping layer (ICL) thickness from 6 to 2 nm in a novel Ru/WN_x ICL/Hf_0.5Zr_0.5O₂(HZO)/TiN structure after annealing at 400 °C in a furnace. This occurs because of the higher orthorhombic (o) plus rhombohedral (r) phases (>70%), which is analyzed by geometrical phase analysis (GPA) of high-resolution transmission electron microscope (HRTEM) images. An optimized 2 nm WN_x ICL memory capacitor shows a low coercive field (E_c) of 1.27 MV cm⁻¹ and long endurance of > 10⁹ cycles (remaining 2P_r value of 13.5 µC cm⁻²) under a low field stress of ±2 MV cm⁻¹ and 0.1 µs hold pulse width (or ≈1.67 MHz). Even this long endurance of > 10⁹ cycles is obtained by applying a higher stress of ±2 MV cm⁻¹, 1 MHz, or 100 kHz. Under ±3 MV cm⁻¹ stress, the mechanism is caused by m-phase growth from both the HZO/TiN bottom electrode (BE) and WN_x ICL/HZO interfaces, which is evidenced by HRTEM images after 2 × 10⁷ cycles for the first time.