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The ferroelectric field-effect transistor (FeFET) is a promising memory technology due to its high switching speed, low power consumption, and high capacity. Since the recent discovery of ferroelectricity in Si-doped HfO 2 thin films, HfO 2 -based materials have received considerable interest for the development of FeFET, particularly considering their excellent complementary metal-oxide-semiconductor (CMOS) compatibility, relatively low permittivity, and high coercive field. However, the multilevel capability is limited by the device size, and multidomain switching tends to vanish when the channel length of the HfO 2 -based FeFET approaches 30 nm. Here, multiple nonvolatile memory states are realized by tuning the electric field gradient across the Hf 0.5 Zr 0.5 O 2 (HZO) ferroelectric thin film along the channel direction of FeFET. The multi-step domain switching can be readily and directionally controlled in the HZO-FeFETs, with a very low variation. Moreover, multiple nonvolatile memory states or multi-step domain switching can be effectively controlled in the FeFETs with a channel length less than 20 nm. This study suggests the possibility to implement multilevel memory operations and mimic biological synapse functions in highly scaled HfO 2 -based FeFETs.

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Because of its unique physical properties, domain wall (DW) in ferroelectrics not only plays a key role in the electrical properties of ferroelectric film but also has shown tremendous prospect in the DW-based memory and logic devices. However, the motion mechanism of ferroelectric DW, which is of great significance for the application of ferroelectric films, has not been clearly understood. In this paper, the 180°DW motions in BaTiO 3 (BTO) and PbTiO 3 (PTO) were studied by using the nudged elastic band method based on the density functional theory. The evolutions of atomic structure, local polarization, and energy of the system for the DW motion process between the two adjacent equilibrium positions were systematically revealed. The DW migration across the oxygen vacancy was also simulated, and the corresponding potential well for the DW motion was obtained. It was also found that the DW motion barrier could be significantly influenced by the in-plane strain. The "activation field" deduced from the energy barrier of DW motion in the present calculation agrees with experimental values, which may provide a fundamental understanding of DW dynamics.

The multilevel memory performances of ferroelectric field effect transistor (FeFET) with Hf 0.5 Zr 0.5 O 2 (HZO) ferroelectric thin film are investigated. First, similar retention characteristics are observed for intermediate and saturated polarization states of HZO ferroelectric thin film, which enables memories for multi-bit data storage. And then, 2-bit/cell operation of HZO-based FeFET is demonstrated utilizing two NAND architecture compatible write schemes of varying program pulse amplitude and width. Low cycle-to-cycle variability, long retention to extrapolation of 10 years at 85 • C, and endurance of 500 cycles are achieved for the both schemes. Moreover, the mechanism for multilevel memory operations of the FeFET is illustrated based on the polarization switching dynamics of HZO ferroelectric thin film. INDEX TERMS FeFET memory, Hf 0.5 Zr 0.5 O 2 , 2-bit/cell, write schemes, retention, endurance. SHUAIZHI ZHENG received the B.S. degree in chemistry and the M.S. degree in inorganic chemistry from Beijing Normal University, China, in 2005 and 2008, respectively, and the academic degree of Doctor of Natural Sciences from the

Flexible HZO ferroelectric films with superior ferroelectricity, retention and fatigue endurance under multiple harsh conditions.

CeO2–HfO2 solid solution thin films, Hf1−xCexO2, are fabricated on n+-Si(100) substrates by the chemical solution deposition method. The effects of the CeO2 content and annealing temperature on the structure and ferroelectric properties of Hf1−xCexO2 are studied. The structural properties are investigated by glancing incidence x-ray diffraction and high resolution transmission electron microscopy, while the chemical states are examined by x-ray photoelectron spectroscopy. The results reveal that the admixture of CeO2 could effectively induce the ferroelectric phase. For Hf0.85Ce0.15O2 fabricated at an annealing temperature of 800 °C, an enhanced remanent polarization (Pr) of ∼20 μC/cm2 (after correction for leakage and parasitics) could be attained. Moreover, Hf0.85Ce0.15O2 demonstrates good endurance behavior, that the polarization does not show obvious degradation over 1 × 109 bipolar switching cycles, at an electric field of 2.9 MV/cm and a frequency of 100 kHz. This work highlights the importance of CeO2–HfO2 solid solution films in HfO2-based ferroelectric thin films.