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

Abstract

This work systematically studies the TiN, Ru, and RuO2 top electrodes (TEs) effects on the ferroelectric properties of Hf0.5Zr0.5O2 (HZO) films. The Ru top electrode significantly improves the ferroelectric performance even with the conventional TiN bottom electrode. The high two‐remanent polarization (2Pr) 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 2Pr value of ≈67 µC cm−2 is achieved. Furthermore, it can endure 1 × 1011 switching cycles while a 2Pr 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 Pr and endurance, a critical issue in ferroelectric doped HfO2‐based films.

Understanding phase evolution of ferroelectric Hf0.5Zr0.5O2 thin films with Al2O3 and Y2O3 inserted layers

“…The deconvolution of these spectra revealed the formation of substantial oxygen-deficient phases (HfO 2−x , ZrO 2− x ). 25,47 These phases originated from the substitutional diffusion of Al 3+ ions into the Hf 4+ and Zr 4+ ion sites, inducing oxygen vacancies to maintain charge neutrality. 48 In contrast, the Hf 4f and Zr 3d spectra of Al3, 5(7.8 nm) samples showed minimal change in their binding energy values, and the deconvolution revealed the formation of minuscule oxygen-deficient phases.…”

“…5(a) and (b). 25,47 As for the diffused Al 2 O 3 cases, the substitutional diffusion of Y 3+ ions into the Hf 4+ and Zr 4+ ion sites generated oxygen vacancies, which reduced the m-phase and enhanced the t-phase. 48 The Y 3d spectra in Fig.…”

“…1–7 Various dopants such as Si, Al, Zr, Y, Gd, Sr, and La are known to induce FE properties, 1,8–14 and the Hf 1− x Zr x O 2 solid solution system has garnered particular attention due to its lower processing temperature and diverse material properties depending on the Hf : Zr composition ratio. 11,15–25 The changing characteristics of Hf 1− x Zr x O 2 thin films, such as dielectric (DE), FE, and field-induced ferroelectric (FFE) properties, are due to the formation of the monoclinic phase (m-phase, space group: P 2 1 /c), orthorhombic phase (o-phase, space group: Pca 2 1 ), and tetragonal phase (t-phase, space group: P 4 2 /nmc ), respectively. Although the m-phase is the thermodynamically stable crystalline phase at 1 atm and room temperature, metastable o- and t-phases were achieved depending on doping concentrations, film thickness, and annealing conditions during fabrication.…”

“…Although the m-phase is the thermodynamically stable crystalline phase at 1 atm and room temperature, metastable o- and t-phases were achieved depending on doping concentrations, film thickness, and annealing conditions during fabrication. 11,15–25 Many studies reported the phase transitions experimentally and theoretically, considering thermodynamic parameters and kinetic transition barriers. It is currently understood that grain size, oxygen vacancy, interfacial/surface energy, and strain/stress could complexly affect the free energy of each phase.…”

Pure ZrO2 Ferroelectric Thin Film for Nonvolatile Memory and Neural Network Computing

“…37 As a result, the trap-assisted leakage current in ZrO 2 can be reduced. 39,40 It can be concluded from Figures 1 and 2 that the ferroelectricity of the RuO 2 /ZrO 2 (∼8 nm)/RuO 2 sample can be further enhanced by increasing the ferroelectric o-phase fraction, such as through electric field cycling. In comparison to the W/ZrO 2 (10 nm)/W structure (j leak of ∼5 × 10 −7 A/cm 2 at 1 MV/cm), 20 the woken-up RuO 2 /ZrO 2 / RuO 2 sample exhibited a lower j leak of ∼2.79 × 10 −8 A/cm 2 at 1 MV/cm.…”