Modulating the Ferroelectricity of Hafnium Zirconium Oxide Ultrathin Films via Interface Engineering to Control the Oxygen Vacancy Distribution

Abstract

Hafnium oxides‐based ferroelectric materials are promising for applications in nonvolatile memory devices. To control the ferroelectricity of such materials, it is necessary to tune their polymorphism, interfacial features, and defect (oxygen vacancy) distribution. A strategy is described for enhancing the ferroelectric properties of polycrystalline hafnium zirconium oxide (HZO) ultrathin films by modifying the oxygen pressure during the device preparation stage, which involves thermal annealing of TiN electrodes that serve as oxygen reservoirs. Microstructural and chemical characterizations along with theoretical analysis reveal that interfacial layers of TiO2−x (or TiOxNy) can characteristically form between the TiN electrode and the HZO thin film, depending on the oxygen treatment conditions. These interfacial layers directly affect the polymorphic distribution of the as‐deposited HZO. In particular, the engineered interfacial TiO2−x layer facilitates the generation and stabilization of ferroelectric orthorhombic phase HZO by promoting the uniform distribution of oxygen vacancies. Electric field cycling tests further highlight the enhanced ferroelectric polarization and coercive voltage following interfacial engineering. The results presented herein demonstrate successful tuning of the structural and interfacial properties of polycrystalline HZO devices, thus enabling control over their ferroelectric characteristics, which is critical for the fabrication of devices with designed functionality.

Retention Improvement of HZO-Based Ferroelectric Capacitors with TiO2 Insets

“…In addition, the calculations of tensile stress also suggested the local epitaxial growth of a fraction of o-phase HZO grains on TiO 2 anatase grains . The increase in the average tensile stress caused by the integration of TiO 2 was also reported by Gaddam et al Another reason for the more effective o-phase stabilization can be the adoption of tetragonal-like oxygen coordination during the adsorption of the Hf reactant on the TiO 2 anatase surface . Note that the formed t-phase is expected to transform relatively easily into the o-phase as a result of subsequent annealing.…”

“… 33 The increase in the average tensile stress caused by the integration of TiO 2 was also reported by Gaddam et al 34 Another reason for the more effective o-phase stabilization can be the adoption of tetragonal-like oxygen coordination during the adsorption of the Hf reactant on the TiO 2 anatase surface. 29 Note that the formed t-phase is expected to transform relatively easily into the o-phase as a result of subsequent annealing. However, to use any of these interpretations to explain, for example, the higher o-phase content in HZO grown on TiO 2 insets, one has to confirm that TiO 2 is crystallized to the anatase phase, which is challenging due to its small thickness.…”

“…However, interfacial inset dielectric layers are expected to affect the HZO film crystallization process and eventually 2 P r . − In this regard, it is worth searching for the insulator inset that leads to improved reliability among such insulators that at least do not diminish the remanent polarization strongly in HZO films. It was demonstrated that integration of the ZrO 2 , , HfO 2 , HfO x N y , , or TiO 2 , layer to the bottom interface causes an increase in the relative ratio of the orthorhombic ferroelectric phase, enhancing the ferroelectricity of HZO-based capacitors. Inserting top and bottom TiO 2 layers even allowed achieving ferroelectricity in the as-deposited ( T dep = 300 °C) HZO .…”

“… 33 Gaddam et al achieved 2 P r ≈ 33 μC/cm 2 in the tri-layer TiN/HfO 2 /HZO/TiO 2 /TiN structures after rapid thermal annealing at a temperature of 350 °C. 34 Lee et al showed that the integration of the TiO 2 layer at the bottom TiN/HZO interface leads to the point defect-induced stabilization of the ferroelectric HZO phase by promoting the uniform lateral distribution of V O , 29 which affects the reliability properties of HZO-based capacitors. Kim et al investigated the endurance of HZO-based capacitors after the ozone treatment of the bottom TiN/HZO interface, achieving ∼10 8 switching cycles at an applied electric field of 3.5 MV/cm without observing a significant wake-up effect or fatigue.…”

An Aqueous Route to Oxygen-Deficient Wake-Up-Free La-Doped HfO2 Ferroelectrics for Negative Capacitance Field Effect Transistors

“…Due to the structural similarities of the c-, t-, and ophases, 26,27 an extended investigation using atomic-resolution scanning transmission electron microscopy (STEM) combined with position-averaged convergent beam electron diffraction (PACBED) and energy dispersive X-ray spectroscopy (EDX) was utilized. 26,28,29 1c and Figure S8) reveal that La is uniformly substituted for the Hf host without segregation and that the doping concentration is ∼7% relative to the Hf. These observations, made from a relatively large field of view, demonstrate that the HLO films grew uniformly with a flat surface, regardless of the solvent.…”