A synergistic interplay between dopant ALD cycles and film thickness on the improvement of the ferroelectricity of uncapped Al:HfO₂ nanofilms

Abstract

The Al:HfO2 ferroelectric nanofilms with different total thicknesses and distributions of Al-rich strips are prepared using atomic layer deposition (ALD) in an uncapped configuration. The synergistic interplay between the number of Al-rich layers and the thickness of total film offers the additional flexibility to boost the ferroelectricity of the resulting Al:HfO2 nanofilms. By carefully optimizing both the ALD cycles for dopant layer and the total film thickness in the preparation, the HfO2 nanofilms in post-deposition annealing can exhibit excellent ferroelectricity. The highest remanent polarization (2Pr) of 51.8 μC cm−2 is obtained in a 19.4 nm thick Al:HfO2 nanofilm at the dopant concentration of 11.1 mol% with a three ALD cycles for Al-rich strips. Remarkable remanent polarization value observed in the uncapped electrode clamping film paves a new way to explore the origin of ferroelectricity in hafnium oxide nanofilms. The observed ferroelectricity of the nanofilm is affected neither by the presence of an interface between the upper electrode and the film nor the choices of the materials of upper electrode in the measurement, ensuring a high flexibility in the designing and fabrication of the relevant devices in the future.

Polarizable Nonvolatile Ferroelectric Gating in Monolayer MoS2 Phototransistors

“…Also, then the film was annealed in an oxygen atmosphere at 750 °C for 30 s to crystallize, as referred to in our previously reported work. 44 The as-grown CVD MoS 2 crystals were spin-coated with poly(methyl methacrylate) (PMMA, molecular weight: 495, Micro-Chem) for 500 ramps per minute (rmp)@10 s and 2000 rmp@50 s. After baking at 180 °C for 90 s, the Si/SiO 2 substrates were etched in 1 mol L −1 KOH solution. Then, the floating PMMA films were lifted off by using Si/Al:HfO 2 substrates.…”

“…The 10.2 nm thick Al:HfO 2 ferroelectric film with 7 mol % Al dopant concentration was directly deposited on heavily doped Si p-substrates by atomic layer deposition (ALD) at 280 °C/20 Pa using liquid tetrakis (diethylamide), hafnium (TDMAH), and trimethyl aluminum (TMA) as the Hf and Al precursors, and O 2 plasma as oxygen source. Also, then the film was annealed in an oxygen atmosphere at 750 °C for 30 s to crystallize, as referred to in our previously reported work . The as-grown CVD MoS 2 crystals were spin-coated with poly­(methyl methacrylate) (PMMA, molecular weight: 495, Micro-Chem) for 500 ramps per minute (rmp)@10 s and 2000 rmp@50 s. After baking at 180 °C for 90 s, the Si/SiO 2 substrates were etched in 1 mol L –1 KOH solution.…”

The Doping Effect on the Intrinsic Ferroelectricity in Hafnium Oxide-Based Nano-Ferroelectric Devices

“…However, they require capping layer stress to stabilize the o-phase, which leads to high manufacturing cost and complicated processes . In Al-doped HfO 2 (HfAlO) thin films, the small atomic radius of Al exerts mechanical stress in HfO 2 unit cells, which stabilizes the o-phase. , Lee et al demonstrated that the ferroelectric phase of HfO 2 films was stabilized by doping aluminum, which has limited solubility, and the aluminum doping concentration significantly influenced the ferroelectricity of the HfO 2 thin films . Celano et al.…”

“…10 In Al-doped HfO 2 (HfAlO) thin films, the small atomic radius of Al exerts mechanical stress in HfO 2 unit cells, which stabilizes the o-phase. 11,12 Lee et al demonstrated that the ferroelectric phase of HfO 2 films was stabilized by doping aluminum, which has limited solubility, and the aluminum doping concentration significantly influenced the ferroelectricity of the HfO 2 thin films. 13 Celano et al used the flexoelectric effect in HfAlO for inducing polar rotations in HfO 2 thin films by applying an external stress.…”

Robust formation of ferroelectric HfO2 films by Y2O3 sub-monolayer lamination

“…Recently, the lamination of Al 2 O 3 films within a HfO 2 layer was found to be effective in obtaining ferroelectricity by local stresses among layers. 27) In addition, nanolamination of HfO 2 and ZrO 2 layers is reported to be effective in obtaining ferroelectricity by the unbalanced Hf-O and Zr-O bonding strength within the film. 28) As mono-or sub-mono layers can be achieved by the self-limiting deposition process in the atomic-layer deposition (ALD) tool, 29,30) the lamination process allows high flexibility for stabilizing the ferroelectric properties.…”