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Ferroelectric HfO 2 -based materials have attracted extensive attention in the research of next-generation nonvolatile memories and logic devices due to their superior scaling properties and compatibility with the CMOS process. However, forming the ferroelectric metastable phase in the thin films of a few nanometers requires clamping of the top and bottom electrodes. As a result, the interface can significantly impact domain structure and polarization, leading to imprinting effects and non-uniform space charge distribution. Here, we have demonstrated how the interface affects the ferroelectric polarization in Hf 0.5 Zr 0·5 O 2 (HZO) thin films produced by ALD and the physical mechanisms behind it. We found that by regulating the quantity of oxygen vacancy content at the top and bottom interfaces of TiN/HZO/TiN ferroelectric capacitors, it is possible to achieve inversion of polarization orientation. By using a spherical aberration-corrected transmission electron microscope and first-principles calculation, we identified that the internal electric field generated by the accumulation of oxygen vacancies at an interface and the asymmetrical electrostatic energy of the interfacial T-phase layer jointly play a role in the ferroelectric polarization orientation. Our results will significantly help the interface engineering of HfO 2 -based ferroelectric thin films and devices. [ABSTRACT FROM AUTHOR]

Atomic-resolution Cs-corrected scanning transmission electron microscopy revealed local shifting of two oxygen positions (OI and OII) within the unit cells of a ferroelectric (Hf0.5Zr0.5)O2 thin film. A reversible transition between the polar Pbc21 and antipolar Pbca phases, where the crystal structures of the 180° domain wall of the Pbc21 phase and the unit cell structure of the Pbca phase were identical, was induced by applying appropriate cycling voltages. The critical field strength that determined whether the film would be woken up or fatigued was ~0.8 MV/cm, above or below which wake-up or fatigue was observed, respectively. Repeated cycling with sufficiently high voltages led to development of the interfacial nonpolar P42/nmc phase, which induced fatigue through the depolarizing field effect. The fatigued film could be rejuvenated by applying a slightly higher voltage, indicating that these transitions were reversible. These mechanisms are radically different from those of conventional ferroelectrics. HfO2-based ferroelectric films are attracting a great deal of attention. Here, the authors conclude that the performance degradation and the possible rejuvenation are ascribed to the reversible transition between polar and antipolar phases. [ABSTRACT FROM AUTHOR]

Hafnia-based ferroelectric (FE) thin films have received extensive attention in both academia and industry, benefitting from their outstanding scalability and excellent CMOS compatibility. Hafnia-based FE capacitors in particular have the potential to be used in dynamic random-access memory (DRAM) applications. Obtaining fine structure characterization at ultra-high spatial resolution is helpful for device performance optimization. Hence, sample preparation by the focused ion beam (FIB) system is an essential step, especially for in situ biasing experiments in a transmission electron microscope (TEM). In this work, we put forward three tips to improve the success rate of in situ biasing experiments: depositing a carbon protective layer to position the interface, welding the sample on the top of the Cu column of the TEM grid, and cutting the sample into a comb-like shape. By these means, in situ biasing of the FE capacitor was realized in TEM, and electric-field-induced tetragonal (t-) to monoclinic (m-) structure transitions in Hf0.5Zr0.5O2 FE film were observed. The improvement of FIB sample preparation technology can greatly enhance the quality of in situ biasing TEM samples, improve the success rate, and extend from capacitor sample preparation to other types. [ABSTRACT FROM AUTHOR]

HfO 2 -based ferroelectric materials have excellent CMOS compatibility and polarization even in ultrathin films, which is regarded as promising candidate material for memory devices and related electronic devices. However, as the ferroelectric layer thickness scaling down, the consistency of device performance is inevitably affected by the complex polyphase and polycrystalline nature of HfO 2 -based ferroelectric thin films. Therefore, obtaining and controlling the texture of HfO 2 -based ferroelectric thin films is extremely important for regulating polarization orientation and improving ferroelectric polarization. In this work, 10 nm Hf 0.5 Zr 0.5 O 2 (HZO) films were prepared by atomic layer deposition (ALD) on Nb-doped SrTiO 3 (NSTO) single crystal substrates. The texture and orientation of HZO films were analyzed through the state-of-the-art spherical aberration corrected transmission electron microscope (Cs-TEM) technique. The domain matching epitaxy between HZO films and NSTO substrate helps eliminate lattice mismatch and residual misfit strain, and ultimately leads to the formation of <112> texture in HZO ferroelectric films. The obtained results represent lattice and interface play an extremely important role in regulating the ferroelectricity of HfO 2 -based films, which provides a way to design ultra-thin HfO 2 -based materials with excellent ferroelectric polarization by controlling the crystal structure and orientation. [ABSTRACT FROM AUTHOR]