Properties Of Ferroelectric Thin Films Research Articles

Integration Of Solution‐Processed BaTiO3 Thin Films with High Pockels Coefficient on Photonic Platforms

AbstractThe heterogeneous integration of ferroelectric BaTiO3 thin films on silicon (Si) and silicon nitride (SiN)‐based platforms for photonic integrated circuits (PICs) plays a crucial role in the development of future nanophotonic thin film modulators. Since the electro‐optic (EO) properties of ferroelectric thin films strongly depend on their crystal phase and texture, the integration of BaTiO3 thin films on these platforms is far from trivial. So far, a conventional integration route using a SrTiO3 template film in combination with high vacuum deposition methods has been developed, but it has a low throughput, is expensive and requires monocrystalline substrates. To close this gap, a cost‐efficient, high‐throughput and scalable method for integrating highly textured BaTiO3 films is needed. Therefore, an alternative method for the integration of highly textured BaTiO3 films using a La2O2CO3 template film in combination with a chemical solution deposition (CSD) process is presented. In this work, the structural and EO properties of the solution‐processed BaTiO3 film are characterized and its integration into an optical ring resonator is evaluated. The BaTiO3 film exhibits a fiber texture, has a large Pockels coefficient (reff) of 139 pm V−1, and integration into a ring resonator‐based modulator shows a VπL of 1.881 V cm and a bandwidth of > 40 GHz. This enables low‐cost, high‐throughput, and flexible integration of BaTiO3 films on PIC platforms and the potential large‐scale fabrication of nanophotonic BaTiO3 thin‐film modulators.

Engineering crystal structure transformation from layered perovskite-like to pyrochlore for electrostatic energy storage

The pyrochlore phase in ferroelectric materials has long been unaccepted as a negative factor. Therefore, every effort was made to eliminate it. Here, based on electrostatic energy storage capacitors, we provide a counter view to evaluate its effects on ferroelectric properties, i.e., the electrostatic energy storage properties of ferroelectric thin films can be significantly improved by a deliberately designed pyrochlore phase. By adjusting the components and annealing temperature to control crystal structure transformation, an energy storage density of 69 J/cm3 and an efficiency of 70.1% were achieved as a pyrochlore-dominated film, along with good temperature and fatigue stability. It is attribute to its relatively low loss and linear ferroelectric polarization behavior, which enhances the breakdown field while reducing the remnant polarization. These results will provide a versatile strategy for the development of ferroelectric thin film energy storage capacitors with high energy storage density, high efficiency, and good fatigue resistance based on crystal structure transformation.

An Adaptation of the Split-Cylinder Resonator Method for Measuring the Microwave Properties of Thin Ferroelectric Films in a “Thin Film—Substrate” Structure

The split-cylinder resonator method was adapted to measure the microwave properties (dielectric permittivity and loss tangent) of thin ferroelectric films on a dielectric substrate. The mathematical model for calculating the resonance frequency of the split-cylinder resonator was adjusted for the “ferroelectric film—substrate” structure. An approach for correcting the gap effect based on calibrating with a single-layer dielectric was introduced and used to study two-layer dielectrics. The prototype of a split-cylinder resonator designed to measure single-layer dielectric plates at a frequency of 10 GHz was presented. The resonator calibration was performed using dielectric PTFE samples and fused silica, and an example of the correction function was suggested. The measurement error was estimated, and recommendations on the acceptable parameter range for the material under investigation were provided. The method was demonstrated to measure the microwave properties of a ferroelectric film on a fused silica substrate.

Domain structures of PbTiO3 and Pb(Zr,Ti)O3 thin films controlled by tensile strain induced by a Sr(Zr,Ti)O3 buffer layer

Thin films of Sr(Zr,Ti)O3 were investigated as buffer layers to induce tensile strain in ferroelectric thin films such as PbTiO3 and Pb(Zr,Ti)O3 to control the domain structure. By tuning the composition of Sr(Zr,Ti)O3, (100)-oriented PbTiO3 and Pb(Zr,Ti)O3 films were obtained, revealing that tensile strain was introduced into the thin films by the lattice of the buffer layer. We propose a methodology for the successive control of tensile stress, which is useful for understanding and controlling the domain structures of ferroelectric films that result in the ferroelectric and piezoelectric properties of ferroelectric thin films.

Rare Earth Doped Lead Zirconate Titanate Thin Films for Memory and Power Device Applications

We fabricated thin films of (PbZr0.53Ti0.47)O3 (PZT) and (PbZr0.53Ti0.47)0.90(LaxSc1-x)0.10O3 where; x= 0, 0.2, 0.4, 0.6 and 0.8 denoted as [abbr. PL10x] PL0, PL2, PL4, PL6, and PL8 respectively on the LSMO buffer layer (bottom electrode) by using a PLD technique. The X-ray diffraction peaks show a single-phase perovskite structure of thin films with a preferred (100) orientation that coincides with the MgO and has tetragonal phase symmetry (P4mm). Pt electrodes were deposited at the top of thin films as top electrodes. We achieved higher dielectric permittivity (ε’) for PL0 and PL6 compared to other compositions. We noticed that the role of increasing lanthanum content (decreasing scandium) resulted in the broadening of ε’ with temperature and ferroelectric phase transition decreased to 450 K. However, the scandium doping alone (PL0) didn’t lower the ferroelectric phase transition. We analyzed the temperature-dependent ε’ using the modified Curie-Weiss law. The PL0, PL6, and PL8 thin film capacitors exhibited relaxor ferroelectric properties that were further supported by the Vogel-Fulcher relation.The P-E hysteresis loops exhibited the role of lanthanum and scandium causing compositional changes in coercive fields. The P-E loops of PZT, PL2, and PL4 exhibited typical ferroelectric features. Whereas, PL0, PL6, and PL8 showed a relaxor ferroelectric behavior which was corroborated by the analysis of the dielectric data. The PL0 and PL6 thin films showed better spontaneous polarization Ps. We achieved superior energy storage performance Ure = 54.63 J/cm3 with η ~ 70% for PL0 and Ure = 26.54 J/cm3 with η ~ 66% for PL8 thin film capacitors. The study demonstrated the idea that by tuning La3+ and Sc3+ the dielectric and ferroelectric properties of thin films can be controlled for suitable electronic applications, such as memory, power devices, and energy storage.

Optical Properties of Ferroelectric Thin Film Prepared by PLD Technique

Optical Properties of Ferroelectric Thin Film Prepared by PLD Technique

Effect of biaxial misfit strain on properties of ferroelectric double gate negative capacitance transistors

In order to continue Moore’s law, the reduction of power consumption has received much attention. It is necessary to develop steep devices that can overcome the “Boltzmann tyranny” and solve the problem of high power consumption of integrated circuits. Negative capacitance field-effect transistors are one of the most promising candidates in numerous steep devices. Strain engineering has been widely studied as an effective means of regulating the properties of ferroelectric thin films. However, the influence of strain on the performance of negative capacitance field-effect transistor has not been clear so far. Therefore, in this work, an analytical model of double gate negative capacitance field-effect transistor (DG-NCFET) regulated by biaxial misfit strain is proposed. Using this model, we investigate the influences of ferroelectric layer thickness and biaxial misfit strain on electrical properties of PbZr<sub>0.5</sub>Ti<sub>0.5</sub>O<sub>3</sub> (PZT)-based and CuInP<sub>2</sub>S<sub>6</sub> (CIPS)-based negative capacitance field-effect transistors (NCFETs), respectively. The results show that for the negative capacitance field-effect transistor based on PbZr<sub>0.5</sub>Ti<sub>0.5</sub>O<sub>3</sub>, when the ferroelectric layer thickness is increased or the compression strain is applied, the subthreshold swing and conduction current are improved, but the tensile strain has the opposite effect. For the negative capacitance field-effect transistor based on CuInP<sub>2</sub>S<sub>6</sub>, its performance is improved when the thickness of the ferroelectric layer is increased or the tensile strain is applied, but the device lags behind under the compressive strain. It is found that the CIPS-based NCFET exhibits better performance than PZT-based NCFET at low gate voltages.

Thickness effect on ferroelectric domain formation in compressively strained K0.65Na0.35NbO3 epitaxial films

In this paper, the influence of thickness in epitaxial ${\mathrm{K}}_{0.65}{\mathrm{Na}}_{0.35}{\mathrm{NbO}}_{3}$ ferroelectric thin films grown on a (110) ${\mathrm{TbScO}}_{3}$ substrate was systematically studied. Detailed atomic force microscopy revealed a complex change in growth mode with increasing film thickness, with the surface roughness remaining 0.30 nm throughout. By combining piezoresponse force microscopy and high-resolution x-ray diffraction, the occurrence of 90\ifmmode^\circ\else\textdegree\fi{} stripe domains was demonstrated for the films with a thickness of \ensuremath{\ge}11 nm, while the domain periodicity is in good agreement with Kittel's law. Furthermore, up to the thickness of 93 nm, elastic strain relaxation induced by the formation of ferroelectric domains was observed, whereas plastic strain relaxation plays only a minor role. As the film thickness increases, three successive phases of ferroelectric domains were observed: (i) irregularly arranged orthorhombic $c$ domains in the thinnest film, (ii) periodically arranged 90\ifmmode^\circ\else\textdegree\fi{} monoclinic ${M}_{C}$ domains up to a thickness of 25 nm, and (iii) a flux closure vortexlike structure in thicker films to achieve the lowest equilibrium energy. These results demonstrate the importance of understanding the lattice relaxation mechanism for intentional tuning of ferroelectric thin film properties.

Coexistence of ferroelectric phases in barium titanate single-domain thin films

In about twenty years, the temperature-misfit strain phase diagrams have become valuable tools to describe ferroelectric thin film properties. The background theoretical approach consists in searching for the position of the global minimum of the potential landscape and deducing the thermodynamically stable phase. In temperature-misfit strain phase diagrams, lines separate the stable phase regions, and the analysis of the polarization continuity properties across these lines allows us to determine the order of phase transition. This work revealed additional important information relative to the properties of first order phase transitions; we determined the limit of stability of the metastable phases and plotted the corresponding lines in the traditional temperature-misfit strain diagrams. These one dimensional boundaries are the analog to the superheating and supercooling temperature points in the context of bulk ferroelectric crystal. We highlight two dimensional coexistence regions adjacent to first order thermodynamic transition lines. The location and the shape of these regions are strongly dependent on the set of parameters used to describe the bulk crystal. We illustrate the interest in the revelation of coexistence regions, showing that the corresponding multi-stability properties could be used to design non-binary memory cells by using barium titanate thin films.

Structural and electrical study of BLT thin film deposited on different substrates by electron gun evaporation

Purpose The purpose of this study was to deposit Bi4Ti3O12 films by electron gun evaporation technique starting from Bi3.25La0.75Ti3O12 as a target without annealing. The films have been deposited on Si(100), on thin film buffer layer of Pt and glass substrates. X-ray diffraction (XRD) was used to analyze structure of the films, which possesses a good structure with (0010) preferred orientation. Electronic behavior of the samples has been studied. Design/methodology/approach The dependence of both the structure and quality of the BLT thin films on different substrates is studied using XRD. The electrical characteristics were determined using capacitance–voltage (C–V) and current–voltage (I–V) measurements at the frequency of 1 MHz. Optical properties of the grown films deposited on glass substrates were characterized by optical transmittance measurements (UV-Vis). Findings The XRD analysis approved the crystallographer structure of the prepared Bi4Ti3O12 films. The optical properties of deposited film (transmittance and the band gap value) are extracted by UV-Vis spectrum. Originality/value High crystalline quality Bi4Ti3O12 films have been obtained using different substrates at room temperature by means of electron gun deposition. The electrical and ferroelectric properties of thin films were studied using I–V and C–V measurements. The band gap has been found to be about 3.62 eV for the studied film deposited on glass substrate. Electron beam evaporation technique is the most interesting methods, once considering many advantages; such as its stability, reproducibility, high deposition rate and the compositions of the films are controlled.

Phase diagrams, superdomains, and superdomain walls in KxNa1-xNbO3 epitaxial thin films

Domains and domain walls play a critical role in determining the functional properties of ferroelectric thin films for various applications. Understanding the formation and structures of the domains and domain walls is of vital importance to manipulating their configurations and exploring their dynamics. When domains assemble into hierarchical structures, the superdomains and superdomain walls emerge, which exhibits exotic morphology and may lead to distinct new behaviors. Here, taking the K0.5Na0.5NbO3 thin films as a model system, we establish the misfit strain-misfit strain phase diagram at different temperatures and study the formation condition, morphological features, and polarization configurations of two types of superdomain structures by using phase-field simulations, which compare well with prior experiments. We show how the superdomain structures can be viewed as superposition of two sets of polytwin structures along well-defined planes. Several types of superdomain walls are identified, which possess different energies and finite thickness in analogy to conventional domain walls. We also show that some superdomain walls can be anomalously wide and electrically conductive. This work can generate new interests in exploring the structures and functionalities of superdomain and superdomain walls in ferroelectric thin films, which can potentially be utilized for next-generation electronic devices.

Emerging Fluorite‐ and Wurtzite‐Type Ferroelectrics: From (Hf,Zr)O2 to AlN and Related Materials

Emerging Fluorite‐ and Wurtzite‐Type Ferroelectrics: From (Hf,Zr)O₂ to AlN and Related Materials

Ferroelectric properties of pure ZrO2 thin films by chemical solution deposition

Ferroelectricity in pure zirconia (ZrO2) thin films, manufactured on Si (100) substrates via the chemical solution deposition method using all-inorganic aqueous salt precursor, has been demonstrated for the first time. The influence of thickness on the crystalline structure and ferroelectric properties of the thin films were measured and showed that they were strongly affected by the film thickness. The structural data indicated that as the film thickness increased from 30 nm to 50 nm, the m-phase fraction increased, and a phase transition from orthorhombic to cubic and then tetragonal occurred near the main diffraction peak of 30.7°. The lowest m-phase fraction of 15.4% was obtained in the pure ZrO2 film with a thickness of 30 nm, and after 103 field cycling, it exhibited the highest relative permittivity of 39.6 as well as the highest residual polarization of 8.5 μC/cm2.

Optimizing Annealing Process for Ferroelectric Y‐Doped HfO2 Thin Films by All‐Inorganic Aqueous Precursor Solution

Abstract10 nm thick yttrium doped HfO2 (Y:HfO2) thin films are prepared on Si (100) substrates by the chemical solution deposition method using all‐inorganic aqueous salt precursors. The influence of the annealing process, consisting of annealing temperature, holding time, and heating rate, on the crystalline structure and ferroelectric properties of thin films is investigated. Results show that the crystalline structure and ferroelectric properties of films exhibit a strong annealing process dependence. The monoclinic phase and asymmetric orthorhombic phase coexist in the films. The annealing process of the best ferroelectric behavior is obtained by using annealing temperature at 700 °C for 30 s with a heating rate of 30 °C s−1 in N2 atmosphere. The film exhibits lowest m‐phase fraction of 17.9%, accompanied with the highest remanent polarization of 21.4 µC cm−2.

Phase Diagrams, Superdomains, and Superdomain Walls in K <sub><i>x</i></sub>Na <sub>1-<i>x</i></sub>Nbo <sub>3</sub> Epitaxial Thin Films

Domains and domain walls play a critical role in determining the functional properties of ferroelectric thin films for various applications. Understanding the formation and structures of the domains and domain walls is of vital importance to manipulating their configurations and exploring their dynamics. When domains assemble into hierarchical structures, the superdomains and superdomain walls emerge, which exhibits exotic morphology and may lead to distinct new behaviors. Here, taking the K0.5Na0.5NbO3 thin films as a model system, we establish the misfit strain-misfit strain phase diagram at different temperatures and study the formation condition, morphological features, and polarization configurations of two types of superdomain structures by using phase-field simulations, which compare well with prior experiments. We show how the superdomain structures can be viewed as superposition of two sets of polytwin structures along well-defined planes. Several types of superdomain walls are identified, which possess different energies and finite thickness in analogy to conventional domain walls. We also show that some superdomain walls can be anomalously wide and electrically conductive. This work can generate new interests in exploring the structures and functionalities of superdomain and superdomain walls in ferroelectric thin films, which can potentially be utilized for next-generation electronic devices.

Strain tuning of negative capacitance in epitaxial PbZr<sub>0.2</sub>Ti<sub>0.8</sub>O<sub>3</sub> thin films

In order to continue Moore’s Law, the reducing of power consumption is concerned by many researchers, and the discovery of ferronegative negative capacitance effect (NCE) provides a solution. Strain engineering has been widely studied as an effective means to regulate the physical properties of ferroelectric thin films. But the relevant mechanism of strain to ferroelectric negative capacitance regulation is not clear. Recently, the experimental results have shown that it is possible to stabilize the transient NCE in resistance-ferroelectric networks. In this work, we use the Landau-Khalatnikov theory to study the microscopic domain evolution and the influence of strain and temperature on NCE in a ferroelectric film. It is shown that compressive strain enhances NCE while NCE becomes weaker under a tensile strain. However, a larger compressive strain will give rise to a higher coercive voltage that hinders the NCE from forming. In addition, under a certain strain, the NCE becomes stronger at lower temperature. This work provides the theoretical basis for designing the negative capacitance devices and scaling towards nanoscale dimensions in future.

Improved piezoelectricity and energy storage performance simultaneously achieved in [001]-preferentially oriented Bi0.5Na0.5TiO3–BaTiO3–BiMnO3 thin films grown on Nb-doped SrTiO3 single-crystalline substrates

The control of grain orientation by introducing Nb-doped SrTiO3 single crystalline substrates is an effective way to improve piezoelectric and ferroelectric properties of thin films. Therefore, in this work, 0.99(0.94Bi0.5Na0.5TiO3–0.06BaTiO3)–0.01BiMnO3 thin films were coated on Pt(111)/TiOx/SiO2/Si(001) polycrystalline substrates and Nb-doped SrTiO3 single crystalline substrates, respectively. The Nb-doped SrTiO3 single crystalline substrates can affect the orientation of the BNT–BT–0.01BMO thin films, promote the grain growth, reduce the leakage current, and form an interfacial layer between the thin film and the substrate, and a comparatively larger converse piezoelectric coefficient (46.49 pm·V−1), a high energy storage density (56.5 J cm-3), and a high energy storage efficiency (79.4 %) were therefore simultaneously achieved in the thin films grown on Nb-doped SrTiO3 single crystalline substrates, promising the oriented thin films broad application prospects.

Phenomenological theory of defect driven flexo-chemical phenomena in ferroics

The review is focused on the phenomenological description of the elastic defects influence on the electrophysical properties of nanosized ferroics. Using the Landau-Ginzburg-Devonshire phenomenological approach we consider the contribution of the elastic defects (e.g. neutral oxygen vacancies) on the phase transitions temperatures, phase diagrams, piezo-resistive, dielectric and polar properties of thin ferroelectric films and nanoparticles. We pay special attention to the role of flexoelectric effect, Vegard strains and stresses, including their synergy, called flexo-chemical coupling, on the defect-driven phenomena in nanoferroics. We explore the influence of mobile charged defects migration (e.g. the drift and diffusion of cations or charged oxygen vacancies) on the domain structure evolution in thin ferroelectric films. Also, we discuss the possibilities of the uncharged elastic defects self-ordering ordering in thin strained oxide films, and show that a thermodynamically stable disordered phase, spatially modulated phases, and long-range ordered phases with defect layers parallel or perpendicular to substrate plane can appear in the phase diagram in dependence on the film-substrate mismatch strain, concentration of elastic defects and Vegard coefficients. Since the long-range ordered ferroic phases can become multiferroic when some elastic dipoles become electric ones, the obtained results open the way to create and control defect-ordered superstructures by the choice of appropriate substrate and defect concentration in thin ferroic films.

Effect of annealing protection atmosphere on the ferroelectric yttrium doped hafnium oxide thin films

The 10 nm thick yttrium doped hafnium oxide (Y:HfO2) thin films, prepared by chemical solution deposition which using all-inorganic aqueous salt reagents, were fabricated on Si (100) substrates. The crystalline structure, chemical composition and ferroelectric properties of thin films, annealed in protection atmosphere of Air, Ar and N2, were examined. Result showed that the crystalline structure and ferroelectric properties of films exhibited a strong annealing protection atmosphere dependence. When compared to annealing protection atmosphere of Air and Ar, the films with the N2 exhibited lowest m-phase fraction of 19.4%, and the highest oxygen vacancy percentage content of 3.06%, accompanied with the highest relative permittivity of 50.9 and the remanent polarization of 14.6 μC/cm2. These excellent ferroelectric properties were correlated with asymmetric orthorhombic phase and the concentration of oxygen vacancy introduced from the nitrogen doping concentration.

Enhanced photovoltaic effects in ferroelectric solid solution thin films with nanodomains

Domain structures in polar materials provide an additional degree of freedom to tune ferroelectric photovoltaic (PV) effects. One of the approaches to control domain structures is to form a solid solution with analogs in different symmetries. In this study, we investigate the influence of domain structures on the PV properties of ferroelectric thin films in the xBaTiO3–(1−x)BiFeO3 (BT–BFO) solid-solution system (x = 0.1 and 0.2). We found that a substitution of BT for BFO substantially decreases the domain size down to several tens of nanometers, leading to an enhanced PV response owing to a marked contribution of the domain-wall PV effect.