Top Electrode Engineering for High-Performance Ferroelectric Hf_0.5Zr_0.5O₂ Capacitors

This work systematically studies the TiN, Ru, and RuO₂ top electrodes (TEs) effects on the ferroelectric properties of Hf_0.5Zr_0.5O₂ (HZO) films. The Ru top electrode significantly improves the ferroelectric performance even with the conventional TiN bottom electrode. The high two-remanent polarization (2P_r) value (≈65 µC cm⁻²) is obtained with the capacitor with Ru TE, which is ≈1.5 times higher than that of the capacitors with the TiN and RuO₂ TEs. Moreover, it does not break down to 1 × 10⁹ cycling with a high cycling electric field of 4.0 MV cm⁻¹, while others do lower cycle numbers. Further enhancement can be achieved by inserting a 2-nm-thick HfON interfacial layer between the HZO film and TiN bottom electrode while keeping the Ru/HZO top interface structure. The capacitor does not break down even at an electric field strength of 4.8 MV cm⁻¹, at which a 2P_r value of ≈67 µC cm⁻² is achieved. Furthermore, it can endure 1 × 10¹¹ switching cycles while a 2P_r value of 45–53 µC cm⁻² is retained. Therefore, this study elucidates that interfacial engineering is an important technology that can overcome the trade-off relationship between P_r and endurance, a critical issue in ferroelectric doped HfO₂-based films.