The weak ferroelectric contribution to the polarization of antiferroelectric lead zirconate (PZO) thin films has been investigated using PUND (Positive Up Negative Down) pulse measurements and hysterons decomposition by First Order Reversal Curves (FORC) technique. The PUND allows decomposing the measured current, obtained from the polarization-electric field loop measurements, into a switching and a non-switching contribution. We show that the weak ferroelectric phase is enhanced when a large electric field has been previously applied to the material, in order to switch from the antiferroelectric to the ferroelectric phase. Using the PUND measurement at fields below the antiferroelectric to ferroelectric phase transition, the polarization loop corresponding only to the ferroelectric switching contribution has been determined revealing that this contribution to the overall polarization is small. FORC measurements, however, indicate that the ferroelectric phase is present at different fields. At low fields, a quite homogeneous distribution of hysterons exists and at large field, a high concentration of hysterons at a field near to the antiferroelectric to ferroelectric phase transition can be seen. Moreover, when changing the delay between pulses of the PUND and the FORC measurements, we show that this weak ferroelectricity contribution is metastable and decreases with time.

In this paper, the field-induced residual ferroelectricity in antiferroelectric lead zirconate thin films has been studied by impedance measurements together with a hyperbolic law analysis, which permits us to extract the different contributions to the material’s complex permittivity. By measuring the Rayleigh coefficient αr, it appears that the residual ferroelectricity is considerably enhanced when the sample has been previously exposed to an electric field close to the antiferroelectric to ferroelectric transition field. This indicates that a part of the material remains ferroelectric after the antiferroelectric–ferroelectric backward transition, which constitutes an additional contribution to polarization. Consequently, a higher domain wall density and mobility can be observed. Measurements after exposition to thermal treatment show that this ferroelectric response is metastable.

We present the design and the simulation of a frequency reconfigurable millimeter waves patch antenna integrating ferroelectric interdigitated capacitors (FIDCs) based on BST (Barium Strontium Titanate) thin films. The capacitors are designed to operate up to 65 GHz, offering tunabilities of the order of 40% for a 100 V bias voltage and with relatively low losses. To ensure maximum frequency agility, FIDC devices are specifically designed and integrated into the excitation circuit of a patch antenna. The DC voltage bias applied on the FIDCs modifies their capacitance values and thus shifts continuously the operating frequency of the antenna, from 26.7 GHz to 31.2 GHz (16.85% frequency agility).

Dielectric, piezoelectric and electrostrictive properties of antiferroelectric lead zirconate thin films, elaborated by sol gel on alumina substrates, have been studied as a function of the driving field magnitude E-AC. Measurement of the displacement shows that the strain for applied fields below the antiferroelectric-ferroelectric transition is relatively small and that its main contribution arises from the electrostrictive effect. At the same time, due to the presence of a residual ferroelectricity, the piezoelectric effect also contributes to the displacement. At higher fields, a large strain is visible which comes mainly from the antiferroelectric to ferroelectric phase transition, the electrostrictive contribution however still being present. Similar to what has been shown for ferroelectric materials, strain versus the square of polarization loops S(P-2) of the studied antiferroelectric material, exhibit hysteresis character due to the 180 degrees domain walls which contribute to polarization but not to strain. Simultaneous measurement of polarization and displacement enables the extraction of the electrostrictive coefficient and a value Q = 0.082 +/- 0.009 m(4) C-2 has been obtained. Subtraction of the pure electrostrictive contribution from the displacement curve allows evidencing that the piezoelectric activity coexists with the electrostrictive effect at low fields. Maximum values of the equivalent piezoelectric coefficients are respectively 93 +/- 3 pm V-1 and 100 +/- 3 pm V-1 for the positive and the negative parts of the curve for a driving field magnitude E-AC = 700 kV cm(-1). (C) 2022 Elsevier B.V. All rights reserved.

In this study, the ferroelectric domain wall contributions to the permittivity is investigated in a PbZrO3 antiferroelectric thin film far from its antiferroelectric-ferroelectric field transition EAF (E ≤ 150 kV/cm). The lattice contribution to the permittivity increases as function of polarization electric field EDC but also presents two additional small peaks. The increase is due to the antiparallel dipoles reoriented along the electric field direction (antiferroelectric contribution) and the two peaks correspond to a ferroelectric butterfly loop. The two phenomena are added to the permittivity, which make it difficult to decorrelate them. The vibration and pinning/unpinning contributions of the domain walls present only a ferroelectric butterfly loops but they do not tend to zero at infinite fields, which suggests that the ferroelectricity does not disappear completely. Dielectric losses decrease as a function of the polarization (Lorentzian function) due to a reduction of the ferroelectric domain walls density.

Domains of antiferroelectric PbZrO3 have been studied. The (111) PbZrO3 has lower field transitions due to the reduction of the angle between the ferroelectric polar axis and the applied electric field. The study of the permittivity reveals also that the (111) PbZrO3 has a higher correlation of dipoles (|Shf| = 0.007) due to the energy gain associated with their orientation. Therefore, the (111) crystallographic orientation is a better choice for obtaining easily switching domain. The dielectric response of the domain walls in the (100) and (111) PbZrO3 are identical because they have the same environment (same grain size and similar defects) and interact in the same way. Only the domain wall density is higher in the (111) PbZrO3 due to its lower crystallographic orientation factor. Different crystallographic directions have more obstacles due to the inhomogeneity of the crystallization and consequently has more nucleation site for domain walls.

In this study, First-Order Reversal Curves (FORC) measurements and impedance spectroscopy coupled to hyperbolic law analysis have been used in order to characterize lead zirconate antiferroelectric thin films elaborated by a sol-gel process. The presence of a weak residual ferroelectric behavior has been shown even if this contribution is not clearly visible on the polarization-electric field loops. Moreover, FORC measurements indicate that the weak ferroelectric phase switch only when the antiferroelectric phase state of the cell is modified. On the other hand, impedance spectroscopy reveals a fairly good distribution of small residual ferroelectric clusters in the material as no coalescence of ferroelectric domains has been observed at low fields. This study aims to show that FORC distribution measurements and impedance spectroscopy coupled to the hyperbolic law analysis are very sensitive and complementary methods for the understanding of the polarization switching dynamics in antiferroelectric materials.

In this study, the dielectric properties of PbZrO3 thin films are studied as a function of the water/acetic acid solvent ratio of the precursor sol–gel solution. By increasing the water ratio from 35/65 to 85/15, the saturation polarization increases from 24.3 to 27.2 µC/cm2 and the antiferroelectric–ferroelectric field transition (EAF) from 528 to 564 kV/cm. When the hydrolysis rate is higher, the antiferroelectric phase is stabilized due to a denser antiferroelectric matrix with lower defects. As the consequence, the energy storage performances are better for a higher hydrolysis rate: the recoverable energy density increases from 6.3 to 10 J/cm3 and the efficiency from 67 to 71%. A higher permittivity and lower dielectric losses confirm also the enhancement of the antiferroelectric matrix when increasing the amount of water in the precursor solution. In order to obtain better energy storage and dielectric properties, it is preferable to have a high ratio water/acetic acid in the precursor sol–gel solution.

We present the realization and analysis of the microwave performances of interdigited varactors integrating thin ferroelectric layers of barium and strontium titanate (BaxSr1−xTiO3). Devices based on ferroelectric films of different compositions (x = 0.8 and x = 0.5) have been characterized in the millimeter-wave domain, from 200 MHz to 110 GHz. By applying different bias voltages, the tunability of the capacitance can reach up to 40% for the Ba0.8Sr0.2TiO3 composition, under relatively low applied electric fields of about 167 kV/cm. These promising characteristics allow the integration of the varactor devices in tunable antennas for a large frequency domain, from the microwaves to the millimeter waves range.

Nous presentons la realisation et l'analyse des performances hyperfrequences de condensateurs interdigites a capacite variable (IDC) integrant des couches minces ferroelectriques de titanate de baryum et strontium (Ba1-xSrxTiO3). Les dispositifs integrant des films avec deux compositions differentes ont ete caracterises sur une plage frequentielle allant de 200 MHz a 67 GHz, en leur appliquant differentes tensions de polarisation. Les resultats montrent des variations de capacites dans le domaine des frequences millimetriques allant jusqu'a 40% sous des champs electriques relativement faibles, de 150 kV/cm. Ces caracteristiques prometteuses permettent d'envisager l'integration de ces composants IDC au sein des antennes millimetriques reconfigurables. I.

Enhancement of lead zirconate (PbZrO3) polarization is achieved by using a titanium seed layer on alumina polycrystalline substrate. Thanks to the reduction of the lattice mismatch between the platinum electrode (3.92 angstrom) and the PbZrO3 films (4.14 angstrom), lead zirconate thin films oriented along the (111) direction with an orientation factor of around 65 % has been obtained. The (111) PbZrO3 presents an increase of 56 % of the polarization compared to the (100) PbZrO3. This enhancement is responsible of the higher recoverable energy storage density obtained in the (111) PbZrO3 thin films (8 J/cm(3) at 600 kV/cm with an efficiency of 72 %). The (111) PbZrO3 also has a higher figure of merit, which indicates that the (111) crystallographic plane is the most favorable direction for energy storage.

In antiferroelectric PbZrO3 thin films, a weak residual ferroelectric phase is often observed on the double hysteresis loop and it is important to know its impact on the dielectric properties. To study this residual phase, a low and homogeneous electric field can be used because antiferroelectric domain walls are not sensitive to homogeneous fields; thus, contributions of ferroelectric domain wall motions to permittivity and dielectric losses can be isolated. In this paper, the hyperbolic law characterization is used on lead zirconate thin films, which present a residual ferroelectric phase. The study shows that domain wall contributions of the ferroelectric phase are small (less than 2% of the total permittivity), but their impacts are very important in the overall dielectric losses (≈26%). These losses are, however, lower than those obtained in pure ferroelectric materials due to a residual state composed of well distributed ferroelectric clusters of small size with no interactions between domain walls.

Based on a Ba(1-x)SrxTiO3 ferroelectric thin film, a discrete tunable surface mounted device (SMD) capacitor has been developed for microwave frequency applications. The proposed SMD topology has the particular advantage of inherent decoupling between the RF signal and the dc biasing voltage, necessary to tune the ferroelectric permittivity. The design and technological development of the SMD component is presented, and the synthesis of the ferroelectric thin film is summarized. Material characterization shows convenient tunability, while low dielectric losses at 10 MHz. The integration of the SMD tunable capacitor into a Planar Inverted-F Antenna has been done in order to evaluate the agility and tunability performance of the antenna.

In this letter, a wide-tuning range planar inverted-F antenna (PIFA) of 17x10mm(2) dimension printed on a Rogers duroid RT5880 substrate is presented. The printed circuit board (PCB) dimensions are 1x60mm(2). First, the antenna is simulated with a localized capacitor and the effect of the capacitor losses on the antenna efficiency is studied. Then, the antenna is simulated with an integrated BaSrTiO3 (BST) tunable capacitor. The obtained results are in very good agreement with those obtained with localized elements. Finally, the BST thin film capacitor is fabricated and mounted on the antenna. The experimental results show a capacitor tunability of 56.7% at a bias voltage of 35V, leading to an antenna agility of 42.2%.

Polycrystalline BaTiO3 thin films were grown solvothermaly on titanium foil by introducing barium hydroxide solution in a Teflon line and allowed to react with the foil during the autoclave process. Different molar concentration of Ba(OH)(2) were investigated: 0.5, 1 and 2 mol center dot L-1 with three heating temperatures: 150, 175 and 200 degrees C. The films were characterized by XRD and revealed characteristic peaks of BTO with a slight preferential orientation along the [00l] directions. The SEM characterizations showed dense thin films with spherical grains. The relative permittivity is about 400 and dielectric losses below 0.05 in the frequency range 10(2) to 10(7) Hz.

Ferroelectric materials are widely used in the paraelectric phase in order to realize tunable capacitors with reduced losses and a low hysteresis effect. Nevertheless, for polycrystalline thin films, the ferro-/para-electric phase transition can be diffuse and some crystallites can exhibit a ferroelectric nature even if the sample seems to be globally in a paraelectric phase. In this case, domain wall motions are responsible for the sensitivity of the dielectric properties to the driving field and are very dissipative phenomena. In this paper, we evaluate, in the high-frequency band, the impact of ferroelectricity on the properties of Ba2/3Sr1/3TiO3 thin films near the phase transition, by measuring the film's dielectric properties as a function of the incident RF power and for different temperatures.