Ferroelectric memory devices have emerged as a promising class of non-volatile memory technologies, offering a unique combination of high-speed operation, low power consumption, and good endurance compared to conventional flash memory. These devices leverage the bistable polarization states of ferroelectric materials to store data, enabling nonvolatile retention while maintaining fast read/write capabilities. The discovery of hafnium-based ferroelectric materials that are fully CMOS compatible and exhibit robust ferroelectricity at nanoscale dimensions has further enhanced their integration and scalability potential. For IoT devices, which require non-volatile state retention under constrained power budgets and frequent interruptions, we propose a novel FeAND memory cell designed to serve as a non-volatile backup for volatile memory. Unlike conventional ferroelectric memories that rely on current sensing, our design directly outputs a voltage signal, eliminating the need for sensing circuits. The cell exhibits a logical AND-like behavior, enabled by an innovative read scheme based on a CMOS inverter. The cell can function as both a non-volatile memory element and a logic gate where one input is permanently stored as a polarization state. This dual functionality enables novel Computing-in-Memory architectures by embedding logic operations directly within the memory array. We validate our design using Cadence Spectre simulations with the GlobalFoundries 28SLP technology.

This work introduces the AFE-PUND measurement method, an original positive up negative down (PUND) protocol intended to accurately study antiferroelectric (AFE) thin-film behavior. As for its FE counterpart, the AFE-PUND method isolates switching currents from nonswitching contributions, enabling a precise extraction of saturation polarization and coercive fields from hysteresis loop curves. In this paper, AFE-PUND was deployed on AFE ZrO2 films of varying thicknesses. The results reveal that saturation polarization increases with film thickness, indicating enhanced domain stability, while endurance cycles showcase the wake-up effect and its eventual fatigue-induced degradation in thicker films. Similarly, coercive fields decrease with thickness, reflecting reduced switching barriers and a sharper transition between the tetragonal and orthorhombic phases. AFE-PUND establishes itself as an extremely valuable method for advancing the understanding and optimization of AFE materials.

Pulsed power technologies demand dielectric capacitors that possess a high energy storage density and efficiency at low applied electric fields/voltages. In this work, we engineered the morphology of lead-free 0.85[0.6Ba(Zr0.2Ti0.8)O3-0.4(Ba0.7Ca0.3)TiO3]-0.15SrTiO3 (BZCT-STO) epitaxial thin films, fabricated using the pulsed laser deposition technique. Through control of the annealing time, we observed both grain shape and size changes, which induced a change in the relaxor behaviour of the BZCT-STO films. The enhanced relaxor behaviour, assigned to the formation of polar nanoregions, was achieved in the film with uniform smaller spherical grains, which is relevant for improved energy storage performance at low electric fields. The dependence of the electric field on the ferroelectric and energy storage properties of the BZCT-STO thin films was investigated. It is found that the LSMO/BZCT-STO/Au capacitor with enhanced relaxor behaviour shows the optimum energy storage performance, attributable to a moderate maximum polarization and remanent polarization difference, and the highest electric breakdown field. An energy storage density of 9.24 J cm-3 with an efficiency of 86.4% at an applied electric field of 1500 kV cm-1 was obtained. The increased energy storage density and efficiency in these BZCT-STO thin film capacitors at a low electric field make them one of the most promising systems reported in the literature for energy storage applications. The results reported here clearly evidence the significant impact of the film morphology on the dielectric, ferroelectric and energy storage properties.

Layers of HfO2 and (Hf,Zr)O2 crystalline nano-particles are synthesized via direct liquid injection atomic layer deposition, and a comprehensive set of structural, chemical, and electrical characterizations is employed to elucidate their phase composition and functional behavior. X-ray photoelectron spectroscopy revealed a compositional contrast between the films: (Hf,Zr)O2 layers contained up to 45% stoichiometric oxide, while pure HfO2 films are dominated by sub-oxides, especially under strongly reducing conditions, in which exclusively sub-oxide phases and p-type semiconducting behavior is revealed. Electrical measurements indicated room-temperature stabilization of polar phases and tetragonal-to-orthorhombic phase transition with a Curie temperature near 200 K. FTIR spectroscopy confirmed the presence of tetragonal and orthorhombic HfO2 phases, providing insight into minor features observed ≈30° (2θ) in X-ray diffraction patterns. Notably, devices incorporating an AlN interlayer demonstrated a significant enhancement in pyroelectric performance, suggesting this strategy to advance the pyroelectric performance of HfO2-based materials, supporting their development for lead-free sensor technologies.

This study demonstrates the effectiveness of AFE-PUND, a revisited Positive Up Negative Down (PUND) protocol for characterizing antiferroelectric (AFE) materials, in analyzing ZrO_2 films across different thicknesses, revealing key trends. The proposed AFE-PUND method enables the isolation of switching currents from non-switching contributions, allowing precise extraction of remanent polarization and coercive field from hysteresis loops. The remanent polarization increases with film thickness, reflecting enhanced domain stability, while endurance cycles highlight the wake-up effect and its eventual degradation due to fatigue in thicker films. Similarly, coercive fields decrease with thickness, indicating reduced switching barriers and a clearer transition between tetragonal and orthorhombic phases. The method provides valuable insights into micro-structural influences, such as defect accumulation, grain size, and domain wall pinning, which critically affect device performance. AFE-PUND thus establishes itself as an essential tool for advancing the understanding and optimization of antiferroelectric materials.

Ferroelectric imprint in Hf0.5Zr0.5O2 (HZO) polycrystalline thin films poses severe reliability challenges to ferroelectric devices, with its underlying mechanisms still under debate. In this study, a novel 3D phase-field modeling framework is presented to investigate the time-dependent imprint phenomenon in HZO thin films. The phase-field model incorporates charge injection and electron tunneling within the polycrystalline phase-field structure, effectively reproducing key experimental trends, including polarization-voltage curve shifts with increasing pause time, together with the recovery process achieved through field cycling. Through comprehensive analysis, the framework contributes to elucidating the complex interplay between the interfacial dielectric layer and electron detrapping mechanisms, which are critical in shaping ferroelectric imprint behavior. These findings enhance the understanding of imprint mechanisms in polycrystalline hafnium oxide and provide strategic insights for improving the performance and long-term reliability of HZO-based ferroelectric devices.

VO2 undergoes a metal‐insulator transition (MIT) at ≈70 °C, which induces large variations in its electrical and wavelength‐dependent optical properties. These features make VO2 a highly sought‐after compound for optical, thermal, and neuromorphic applications. To foster the development of VO2‐based devices for the microelectronic industry, it is also imperative to integrate VO2 on silicon. However, high lattice mismatch and the formation of silicates at the interface between VO2 and Si degrade the quality and functionality of VO2 films. Moreover, VO2's polymorphic nature and stable VO phases pose integration issues. To address these challenges, the MIT of VO2 thin films integrated on Si with a complementary metal‐oxide semiconductor‐compatible HfxZr1−xO2 (HZO) buffer layer is investigated. Using in situ high‐resolution X‐ray diffraction and synchrotron far‐infrared spectroscopy, combined with multiscale atomic and electronic structure characterizations, it is demonstrated that VO2 on the HZO buffer layer exhibits an unusually low thermal hysteresis of ≈4 °C. In these results, the influence of strain on M2 phase nucleation, which controls the hysteresis, is unraveled. Notably, the rate of phase transition is symmetric and does not change for the heating and cooling cycles, implying no incorporation of defects during cycling, and highlighting the potential of an HZO buffer layer for reliable operation of VO2‐based devices.

In the quest for thinner and more efficient ferroelectric devices, Hf0.5Zr0.5O2 (HZO) has emerged as a potential ultrathin and lead-free ferroelectric material. Indeed, when deposited on a TiN electrode, 1-25 nm thick HZO exhibits excellent ferroelectricity capability, allowing the prospective miniaturization of capacitors and transistor devices. To investigate the origin of ferroelectricity in HZO thin films, we conducted a far-infrared (FIR) spectroscopic study on 5 HZO films with thicknesses ranging from 10 to 52 nm, both within and out of the ferroelectric thickness range where ferroelectric properties are observed. Based on X-ray diffraction, these HZO films are estimated to contain various proportions of monoclinic (m-), tetragonal (t-), and polar orthorhombic (polar o-) phases, while only the 11, 17, and 21 nm thick are expected to include a higher amount of polar o-phase. We coupled the HZO infrared measurements with DFT simulations for these m-, t-, and polar o-crystallographic structures. The approach used was based on the supercell method, which combines all possible Hf/Zr mixed atomic sites in the solid solution. The excellent agreement between measured and simulated spectra allows assigning most bands and provides infrared signatures for the various HZO structures, including the polar orthorhombic form. Beyond pure assignment of bands, the DFT IR spectra averaging using a mix of different compositions (e.g., 70% polar o-phase +30% m-phase) of HZO DFT crystal phases allows quantification of the percentage of different structures inside the different HZO film thicknesses. Regarding the experimental data analysis, we used the spectroscopic data to perform a Kramers-Kronig constrained variational fit to extract the optical functions of the films using a Drude-Lorentz-based model. We found that the ferroelectric films could be described using a set of about 7 oscillators, which results in static dielectric constants in good agreement with theoretical values and previously reported ones for HfO2-doped ferroelectric films.

Over the last fifteen years, ferroelectric (FE) and antiferroelectric (AFE) ultra-thin films based on fluorite-structured materials have drawn significant attention for a wide variety of applications requiring high integration density. AFE ZrO2, in particular, holds significant promise for nanosupercapacitors, owing to its potential for high energy storage density (ESD) and high efficiency (η). This work assesses the potential of high-performance Hf1−xZrxO2 thin films encapsulated by TiN electrodes that show linear dielectric (LD), FE, and AFE behavior. A wake-up effect is observed for AFE ZrO2, a phenomenon barely reported for pure zirconium oxide and AFE materials in general, correlated with the disappearance of the pinched hysteresis loop commonly observed for Zr-doped HfO2 thin films. ESD and η are compared for FE, AFE, and LD samples at the same electrical field (3.5 MV/cm). As expected, ESD is higher for the FE sample (95 J/cm3), but η is ridiculously small (≈55%) because of the opening of the FE hysteresis curve, inducing high loss. Conversely, LD samples exhibit the highest efficiency (nearly 100%), at the expense of a lower ESD. AFE ZrO2 thin film strikes a balance between FE and LD behavior, showing reduced losses compared to the FE sample but an ESD as high as 52 J/cm3 at 3.5 MV/cm. This value can be further increased up to 84 J/cm3 at a higher electrical field (4.0 MV/cm), with an η of 75%, among the highest values reported for fluorite-structured materials, offering promising perspectives for future optimization.

This operando study of epitaxial ferroelectric Pb(Zr0.48Ti0.52)O-3 capacitors on silicon substrates studies their structural response via synchrotron-based time-resolved X-ray diffraction during hysteresis-loop measurements in the 2-200 kHz range. At high frequencies, the polarization hysteresis loop is rounded and the classical butterfly-like strain hysteresis acquires a flat dumbbell shape. We explain these observations from a time-domain perspective: The polarization and structural motion within the unit cell are coupled to the strain by the piezoelectric effect and limited by domain wall velocity. The solution of this coupled oscillator system is derived experimentally from the simultaneously measured electronic and structural data. The driving stress sigma(FE)(t) is calculated as the product of the measured voltage U(t) and polarization P(t). Unlike the electrical variables, sigma(FE)(t) and eta(t) of the ferroelectric oscillate at twice the frequency of the applied electrical field. We model the measured frequency-dependent phase shift between eta(t) and sigma(FE)(t).

Abstract Hafnium zirconium oxide (HZO) is an ideal candidate for the implementation of ferroelectric memristive devices, due to its compatibility with the complementary metal‐oxide‐semiconductor technology. Ferroelectricity in HZO films is significantly influenced by the properties of electrode/HZO interfaces. Here, the impact of the interfacial microstructure and chemistry on the ferroelectricity of 6 nm‐thick HZO‐based capacitors, realized by sputtering, with titanium nitride or tungsten electrode materials, is investigated. The results highlight a strong correlation between the structural properties of electrode/HZO interfaces and the HZO ferroelectric performance. Interface effects become significant at low HZO thickness, thus the precise control over the quality of electrode/HZO interfaces allows the remarkable improvement of HZO ferroelectric properties. A double remanent polarization of 40 µC cm−2 is achieved. This work is a new step towards high quality ultra‐thin HZO films with enhanced ferroelectricity for the implementation of ferroelectric tunnel junctions for brain‐inspired computing.