In this work, we explore the ferroelectric properties of zirconium dioxide ($\text{ZrO}_{2}$) thin films for application in electrooptic (Pockels) modulation. $\text{ZrO}_{2}$ is a compatible material already in use in CMOS foundries as high K oxide. The $\text{ZrO}_{2}$ films were grown via pulsed laser deposition (PLD), and their compatibility and integration with the silicon photonics platform were investigated.

Tailoring at will polar textures in ferroelectrics is critical for the development of nanoscale electronics and functional oxide technologies. Freestanding ferroelectric membranes have enabled studies of strain-induced polarization responses, but the control over membrane shape and local polarization typically remains limited to spontaneous buckling or uniaxial mechanical deformations. In this work, we employ a versatile photosensitive-polymer patterning approach to impose programmable bending strain profiles in ferroelectric membranes. Using BaTiO3 as a model system, we demonstrate deterministic 90° polarization rotation driven by engineered in-plane strain, and 180° polarization reversal arising from flexoelectric coupling through a controlled strain gradient. These results establish this programmable bending as a powerful approach to investigate strain-dependent domain structures, leverage flexoelectric effects, and engineer custom ferroelectric landscapes across a wide range of oxide membranes.

Ferroelectric memristive devices based on hafnia are promising systems for neuromorphic electronics, yet the interplay between polarization-modulated resistive changes and defect-mediated transport often leads to complex and debated switching mechanisms. Here, we investigate this competition in epitaxial Hf_0.5Zr_0.5O_2/La_0.67Sr_0.33MnO_3 heterostructures with Pt top electrodes by combining structural, ferroelectric, and memristive characterization with a statistical analysis across a broad range of device areas spanning three orders of magnitude. We identify two distinct memristive regimes with opposite resistance–voltage chiralities. Small devices exhibit a low-resistance state that scales inversely with area, consistent with area-distributed tunneling transport, while larger devices display an area-independent resistance indicative of localized conductive channels. A statistical nucleation model quantitatively captures this behavior and yields a crossover characteristic area A^* ≈ 10^3 μm^2. This crossover also correlates with the onset of ferroelectric wake-up in larger devices, linking conductive-channel nucleation and oxygen-vacancy redistribution within a unified physical picture. These results establish lateral device size as a key parameter controlling the dominant transport mechanism in epitaxial hafnia-based devices.

The continuous expansion of digital infrastructures and advanced technologies has dramatically increased worldwide energy consumption, raising urgent environmental and geopolitical concerns. Addressing this challenge requires the development of highly efficient photonic components capable of reducing power usage in data processing, communication, and adaptive optical systems. In this regard, optical modulators and amplifiers are fundamental building blocks in integrated photonics, as they enable dynamic light management with reduced energy requirements. Ionic-based light-emitting devices represent a particularly promising strategy for low-power optical modulation. These systems rely on reversible redox reactions triggered by small applied voltages, allowing controlled modification of their optical properties. Importantly, their optical states can remain stable without continuous electrical bias, providing a nonvolatile response that significantly lowers energy consumption compared to conventional emissive display technologies. Oxides doped with rare-earth elements have emerged as attractive candidates for such applications, as they combine efficient ionic-electronic transport with sharp and tunable optical emissions. Here, we show that yttria-stabilized zirconia doped with Pr and Tb, when incorporated into silicon- compatible device platforms, operates effectively as an active medium for visible light emission. Beyond display functionalities, these materials exhibit strong emission features suitable for adjustable and nonvolatile optical gain, opening pathways toward ionically controlled tunable laser systems. Together, these results position rare-earth-doped YSZ as a highly adaptable material system for the next generation of low-power, multifunctional photonic devices.

Ferroelectrics are polar materials whose polarization can be switched by applying electric fields; they offer unique opportunities to develop performant photostrictive materials, i.e., materials that can deform under visible light illumination. Naturally devoid of inversion symmetry, they exhibit original photogalvanic effects such as the Bulk Photovoltaic Effect, which relies on “hot” photoexcited carriers. It has long been thought that the electric field generated by this effect may couple to the natural piezoelectric abilities of ferroelectrics to provide large photoinduced deformations. However, due to competing effects, such as thermal dilatation, deformation potential, polarization, or depolarizing-field screening by thermalized carriers, it remains unclear which microscopic phenomena govern the photoinduced deformations in classical ferroelectric materials. Here, we demonstrate the largest photoinduced deformation measured in a ferroelectric thin film. Reaching 1

Electric-field-induced phase transitions are the most important characteristics of antiferroelectric materials, furnishing them with rich functional properties. While they are actively studied for their potential applications such as high-strain transducers and electrocaloric devices, the applied electric field needed to reach the polar phase makes structural studies throughout the full transition of utmost importance. Here, the evolution of both structure and strain in antiferroelectric PbZrO3 thin films was investigated by in situ synchrotron x-ray diffraction during electrical actuation up to 700 kV/cm applied DC electric field. The ferroelectric phase, characterized by its polar order and resulting piezoelectric activity, was found to nucleate at an electric field of 200 kV/cm and to disappear below 160 kV/cm, showing a hysteretic behavior. The variation of the different Bragg peak widths of antiferroelectric and ferroelectric phases revealed the variation of strain distributions in the thin film where antiferroelectric and polar regions coexist during the phase transformation. In addition, the effective longitudinal piezoelectric coefficient of the ferroelectric phase itself, which remains inaccessible by classical macroscopic interferometric measurements, was determined for the first time and reached a value of 67 pm/V, which is quite significant for a thin film clamped on a substrate. These findings provide a clearer understanding of the dynamics of the electric-field-induced phase transition in antiferroelectric PbZrO3 thin films.

Heterogeneous integration of Erbium doped yttria-stabilized-zirconia superlattice on SiN is presented for light amplification. First, a material study was performed to optimize emission at telecom wavelength followed by integration study.

In this work, we present a comprehensive and comparative study on the growth and magnetic properties of CoFe2O4 layers deposited on both undoped and self-oxidized N-doped BaTiO3 films grown on La2/3Sr1/3MnO3/ SrTiO3 (001) substrates, a prototypical magneto-electric multiferroic system. The oxide layers were grown by plasma-assisted molecular beam epitaxy. We show that N doping, even at a low level of 1 %, induces substantial changes in growth modes and strain relaxation in BaTiO3 and consequently in the CoFe2O4 top layer, which exhibits enhanced magnetization and reduced magnetocrystalline anisotropy. The magnetic properties were determined from extensive element-specific magnetic X-ray dichroic measurements, which were simulated through crystal field multiplet calculations. The structural properties of the samples were investigated using grazing incidence X-ray diffraction and high-resolution electron microscopy. Our observations provide evidence that the plastic relaxation of the underlying ferroelectric N-doped BaTiO3 layer affects the magnetic properties of the top CoFe2O4 layer and can serve as an additional tuning parameter for manipulating the expected properties of multiferroics.

Freestanding ferroelectric membranes have emerged as a versatile tool for strain engineering, enabling the exploration of ferroelectric properties beyond traditional epitaxy. The resulting ferroelectric domain patterns stem from the balance at the local scale of several effects playing a key role, i.e., piezoelectricity linked to strain, and flexoelectricity arising from strain gradients. To weigh their respective contributions for a given membrane geometry, the strain profile has to be mapped with respect to the ferroelectric polarization landscape, a necessary step to allow for a controlled tailoring of the latter. In this study, the effect of bending strain on a Pb(Zr,Ti)O 3 membrane is examined in a fold‐like structure, observing a polarization rotation from out‐of‐plane to in‐plane at the fold apex. Combining piezoresponse force microscopy, Raman spectroscopy, and scanning transmission electron microscopy, the ferroelectric polarization direction is mapped relative to the height profile of the membrane and the contributions of strain and strain gradients for this archetypal fold geometry are discussed. These findings offer new insights into strain‐engineered polarization configurations and emphasize strain effects at the nanoscale to tune the functional properties in freestanding membranes beyond conventional electrical methods.

Epitaxial oxynitride films have promising genuine electronic properties but are very challenging to engineer due to a detrimental imbalance between nitriding and oxidation. The crystalline growth of BaTiO3 thin films doped by atomic and ion-nitrogen plasma-assisted molecular beam epitaxy has been studied on SrTiO3(001) substrates. Several conditions for nitrogen insertion in the perovskite lattice of BaTiO3 were considered. The N-doped BaTiO3 layers are compared to undoped BaTiO3 films produced with an atomic oxygen plasma source only. Oxynitride layers were elaborated on two different perovskite surfaces: SrTiO3(001) single crystal substrates and a La2/3Sr1/3MnO3 back electrode on SrTiO3(001). This approach permits an in-depth study of the films' specific properties including crystalline structure, chemical composition, ferroelectric behavior, and optical response. The chemistry and crystalline structure of the films are found to depend modestly on the substrate nature, while the growth is strongly dominated by self-oxidation and the presence of the ca. 1% substitutional nitrogen (N) in the oxynitride films. Structural and ferroelectric properties are similar for N-doped and undoped BaTiO3 films, while significant changes in optical absorption are observed upon N-doping, confirming recent theoretical predictions. This new class of compounds is expected to be very well suited for novel applications based on band engineering in multifunctional materials.

Here, we exploit the Ferroelectric properties in Zirconium Dioxide (ZrO2) thin films for electro-optic (Pockels) modulation. ZrO2 was deposited using pulsed laser deposition technique and its integration in the integrated silicon photonic platform was studied.

We present a fundamental study of the band alignment at the interface of HfZrO4 (HZO) with Ge-doped Ga2O3. Ge is an alternative n-type dopant for the wide band gap Ga2O3 due to its shallow donor level and favorable MBE growth conditions. In the perspective of using the ferroelectric polarization of hafnia based oxides, we have used a stack of HZO on highly Ge doped Ga2O3, the latter providing high carrier density. Electrical contacts were ensured by a TiN top electrode deposited on the HZO and an Au pad on the Ge:Ga2O3. The band alignment was measured by carrying out hard X-ray photoelectron spectroscopy (HAXPES) with in situ bias application across the HZO and following the evolution of both HZO and Ga2O3 energy level. Complementary high-resolution transmission electron microscopy (HRTEM) provided structural confirmation of the polar orthorhombic phase however electrical characterization showed that charge injection and trapping at the interface prevents stabilizing the ferroelectric polarization in HZO. The band alignment in the presence of a leaky HZO layer is therefore dominated by the bias induced band skewing.

The rapid advancement of modern technology has led to a steep rise in global energy demand, posing serious challenges related to climate change and the geopolitical complexities of energy sourcing. In this context, modulators and optical amplifiers have become essential components in next-generation photonic chips, playing a pivotal role in improving energy efficiency across diverse applications ranging from telecommunications to smart window technologies. In particular, optical modulators are critical for controlling light intensity with high precision while minimizing power consumption, thereby contributing to the development of sustainable photonic systems. Among various modulation technologies, light emitting devices based on ionics stand out due to their ability to modulate light using low-voltage, reversible redox reactions. These devices offer significant energy savings over traditional light-emitting displays, as they require no constant voltage to maintain their optical state. Recent research has highlighted the potential of rare-earth-doped oxides, especially those combining the robust ionic-electronic conductivity of mixed ionic-electronic conductors with the optical tunability of RE ions. In this study, we demonstrate that Er- Pr- and Tb-doped yttria-stabilized zirconia integrated into silicon compatible structures are effective active layers in visible-light-emitting displays. Additionally, these rare-earth-doped materials exhibit strong visible light emission wavelengths which can be used for tunable and nonvolatile optical amplification and tunable lasers using ionics. These results highlight the versatility and performance potential of RE-doped YSZ as a multifunctional material platform for future photonic devices.

Abstract The crystal structure and ferroelectric properties of epitaxial ZrO2 films ranging from 7 to 42 nm thickness grown on La0.67Sr0.33MnO3 buffered (110)‐oriented SrTiO3 substrate are reported. By employing X‐ray diffraction, a tetragonal phase (t‐phase) at all investigated thicknesses, with slight in‐plane strain due to the substrate in the thinnest films, is confirmed. Further confirmation of the t‐phase is obtained through infrared absorption spectroscopy with synchrotron light, performed on ZrO2 membrane transferred onto a high resistive silicon substrate. Up to a thickness of 31 nm, the ZrO2 epitaxial films exhibit ferroelectric behavior, at variance with the antiferroelectric behavior reported previously for the t‐phase in polycrystalline films. However, the ferroelectricity is found here to diminish with increasing film thickness, with a polarization of 13 µC cm−2 and down to 1 µC cm−2 for 7 and 31 nm thick ZrO2 films, respectively. Given that the t‐phase is nonpolar, the observations emphasize the influence of external factors, in promoting polarization in t‐ZrO2 thin films. These findings provide new insights into the ferroelectric properties and structure of ZrO2 thin films, and open up new directions to investigate the origin of ferroelectricity in ZrO2 and to optimize this material for future applications.

Understanding various aspects of ferroelectricity in hafnia-based nanomaterials is of vital importance for the development of future non-volatile memory and logic devices. Here, the unconventional and weak electromechanical response of epitaxial La_0.67Sr_0.33MnO_3/Hf_0.5Zr_0.5O_2/La_0.67Sr_0.33MnO_3 ferroelectric capacitors is investigated, via the sensitivity offered by nanobeam X-ray diffraction experiments during application of electrical bias. It is shown that the pristine rhombohedral phase exhibits a negative linear piezoelectric effect with piezoelectric coefficient (d_33) -0.5 to -0.8 pmV^-1. First-principles calculations support an intrinsic negative piezoresponse. In addition, it is found that the piezoelectric response is suppressed above the coercive voltage. For higher voltages, and with the onset of DC conductivity throughout the capacitor, a second-order effect is observed. The electromechanical response observed in this work is clearly different from that of normal ferroelectrics, again underlining the unconventional nature of polarization switching in the samples.

This study investigates ultrafast photoinduced changes in optical properties of ferroelectrics (PZT) on femtosecond to nanosecond timescales, using broadband transient reflectivity studies. Surprisingly, spectral features were observed below the bandgap, which could not be attributed to ground state bleaching, excited state absorption, and/or stimulated emission. A model based on probe energy independent changes in refractive index and extinction coefficient showed good agreement with experimental results. Three relaxation processes were phenomenologically considered for the temporal evolution. Laser-induced heating was ruled out as the cause of short timescale behavior and photorefractive effect was suggested as a potential mechanism for changes in the optical properties. Graphical abstract