Showing papers on "Ferroelectricity published in 1995"

Fatigue-free ferroelectric capacitors with platinum electrodes

Abstract: A SIGNIFICANT fraction of the computer memory industry is at present involved in the manufacture of non-volatile memory devices1—that is, devices which retain information when power is interrupted. For such applications (and also for volatile memories), the use of capacitors constructed from ferroelectric thin films has stimulated much interest1. In such structures, information is stored in the polarization state of the ferroelectric material itself, which should in principle lead to lower power requirements, faster access time and potentially lower cost1. But the use of ferroelectrics is not without problems; the memories constructed to date have generally suffered from poor retention of stored information and degradation of performance ('fatigue') with use1–3. Here we describe the preparation and characterization of thin-film capacitors using ferroelectric materials from a large family of layered perovskite oxides, exemplified by SrBi2Ta2O9, SrBi2NbTaO9 and SrBi4Ta4O15. The structural flexibility of these materials allows their properties to be tailored so that many of the problems associated with previous ferroelectric memories are avoided. In particular, our capacitors do not show significant fatigue after 1012 switching cycles, and they exhibit good retention characteristics and low leakage currents even with films less than 100 nm thick.

Ferroelectric Polymers : Chemistry: Physics, and Applications

Abstract: Part 1 Ferroelectric Polymers: Polymer Electrets Crystal Structures and Phase Transitions of PVDF and Related Copolymers Ferroelectric, Pyroelectric, and Piezoelectric Properties of Poly(vinylidene Fluoride) PVDF and Its Blends Poly(trifluoroethylene) Ferroelectric Nylons Cyanopolymers Polyureas and Polythioureas Piezoelectricity and Pyroelectricity Ferroelectric Liquid Crystal (FLC) Polymers Polymer-Ferroelectric Ceramic Composites Nonlinear Optical Properties of Ferroelectric Polymers Dielectric Properties of Ferroelectric Polymers. Part 2 Applications Pyroelectric Applications Electromechanical Applications Transduction Applications Ferroelectric Optical Memory Biomedical and Robotic Applications of Ferroelectric Polymers Applications of Ferroelectric Liquid Crystalline Polymers.

Ferroelectric/ferroelastic interactions and a polarization switching model

Abstract: Ferroelectric and ferroelastic switching cause ferroelectric ceramics to depolarize and deform when subjected to excessive electric field or stress. Switching is the source of the classic butterfly shaped strain vs electric field curves and the corresponding electric displacement vs electric field loops [1]. It is also the source of a stress—strain curve with linear elastic behavior at low stress, non-linear switching strain at intermediate stress, and linear elastic behavior at high stress [2, 3]. In this work, ceramic lead lanthanum zirconate titanate (PLZT) is polarized by loading with a strong electric field. The resulting strain and polarization hysteresis loops are recorded. The polarized sample is then loaded with compressive stress parallel to the polarization and the stress vs strain curve is recorded. The experimental results are modeled with a computer simulation of the ceramic microstructure. The polarization and strain for an individual grain are predicted from the imposed electric field and stress through a Preisach hysteresis model. The response of the bulk ceramic to applied loads is predicted by averaging the response of individual grains that are considered to be statistically random in orientation. The observed strain and electric displacement hysteresis loops and the nonlinear stress—strain curve for the polycrystalline ceramic are reproduced by the simulation.

Preparation and ferroelectric properties of SrBi2Ta2O9 thin films

Abstract: Ferroelectric SrBi2Ta2O9 thin films were synthesized on Pt/Ti/SiO2/Si substrates using a solution deposition process, and structural and electrical properties were investigated. The spin‐on films crystallized during firing above 700 °C. The films showed high diffraction peaks of (105) and (200), while little peaks from (00l) planes were observed. Good ferroelectric properties were obtained for a 280 nm thick film; Pr and Ec were 10.0 μC/cm2 and 38 kV/cm, respectively. Fatigue endurance was excellent; the hysteresis loop does not change up to 109 switching cycles. These properties are very attractive for nonvolatile memory application.

Size-induced diffuse phase transition in the nanocrystalline ferroelectric PbTiO 3

Abstract: We report a detailed study of the size dependence of the ferroelectric transition in an ensemble of ${\mathrm{PbTiO}}_{3}$ nanoparticles produced by coprecipitation. The phase transition was monitored by dielectric measurements, variable temperature x-ray diffraction, and differential scanning calorimetry (DSC). Size effects were found to become important only below \ensuremath{\approxeq}100 nm (coherently diffracting x-ray domain size). The tetragonal distortion of the unit cell (which is related to the spontaneous polarization) decreases exponentially with size and vanishes at 7 nm. The ${\mathit{T}}_{\mathit{c}}$ decreases gradually but the transition becomes increasingly diffuse with a decrease in the size from 80 to 30 nm, below which there is no peak in the dielectric constant or the heat flow (DSC), though ferroelectric ordering probably persists down to \ensuremath{\approxeq}7 nm.

Competing structural instabilities in cubic perovskites.

Abstract: We study the antiferrodistortive instability and its interaction with ferroelectricity in cubic perovskite compounds Our first-principles calculations show that coexistence of both instabilities is very common We develop a first-principles scheme to study the thermodynamics of these compounds when both instabilities are present, and apply it to SrTi${\mathrm{O}}_{3}$ We find that increased pressure enhances the antiferrodistortive instability while suppressing the ferroelectric one Moreover, the presence of one instability tends to suppress the other A very rich $P$- $T$ phase diagram results

The Influence of the Microstructure on the Properties of Ferroelectric Ceramics

Abstract: Conventional ferroelectric perovskite type ceramics have dielectric, piezoelectric and elastic properties which depend on grain size and on domain configuration. Very fine grained ceramic is not splitted in domains. This causes strong elastic stress fields in the grains which counteract ferroelectricity. Tetragonal fine grained ceramic has a simple laminar domain structure and high elastic stress fields inside the grain and at the grain boundaries. These stress fields cause very high permittivity. In coarse grained ceramics the stress fields inside the grain are eliminated by a three-dimensional network of domains. In fine and in coarse grained ceramics the domain walls contribute considerably to the dielectric, piezoelectric and elastic constants at frequencies below a relaxation frecuency which is between 200 and 1000 MHz. At low temperatures, however, the domain wall contributions freeze in. Acceptor doping lowers the domain wall contributions and shifts the relaxation frequency to higher values. The properties of the conventional ceramics will be compared wiht properties of thin firms and with properties of relaxor ceramics.

The positive temperature coefficient of resistivity in barium titanate

Abstract: Positive temperature coefficient of resistivity (PTCR) materials have become very important components, and among these materials barium titanate compounds make up the most important group. When properly processed these compounds show a high PTCR at the Curie temperature (the transition temperature from the ferroelectric tetragonal phase to the paraelectric cube phase). In the first half of this paper literature related to the resistivity-temperature behaviour is discussed. As explained by the well established Heywang model, the PTCR effect is caused by trapped electrons at the grain boundaries. From reviewing experimental results in the literature it is clear that the PTCR effect can not be explained by assuming only one kind of electron trap. It is concluded that as well as barium vacancies, adsorbed oxygen as 3d-elements can act as electron traps. In the second half of this paper, the influence of the processing parameters on the PTCR related properties is discussed. Special emphasis is placed on the phenomenon that the conductivity and grain size decrease abruptly with increasing donor concentration above ∼ 0.3 at%. Several models explaining this phenomenon are discussed and apparent discrepancies in experimental data are explained.

Voltage offsets in (Pb,La)(Zr,Ti)O3 thin films

Abstract: Cooling (Pb,La)(Zr,Ti)O3 films from their pulsed laser deposition temperature in a reducing ambient yields a voltage offset in the polarization–voltage characteristics. Reversing the as‐processed polarization at 120 °C nearly removes the offset. By reversing the polarization at room temperature and either heating the film at zero voltage or illuminating the film with UV light, the offset can be partially changed. All changes are recoverable using the same processes with opposite polarity polarization. This behavior is explained by a process‐induced accumulation of oxygen vacancies at one interface, oxygen vacancy defect‐dipole complexes throughout the film, and trapping of free electrons at the interface of positive polarization. Voltage offset and shift effects are not observed in films cooled in 1 atm of oxygen

Identification of Passive Layer in Ferroelectric Thin-Films from Their Switching Parameters

Abstract: The switching of the sandwich structure ''ferroelectric+thin dielectric layer'' is theoretically studied. The behavior of the remanent polarization, P-r, coercive field, E(c), maximal polarization on the loop, P-s, and the slope of the hysteresis loop at E(c) as a function of both, the relative thickness of the layer (the thickness of the dielectric divided by the thickness of the ferroelectric) and the amplitude of the measuring field, is analyzed. It is shown that the effect of the layer on P-r and the slope at E(c) is qualitatively different from that on E(c) and P-s. As the result of this analysis the set of characteristic features of the sandwich with the variable relative thickness of the dielectric layer have been have formulated. These characteristic features can be used for the identification of the presence of such a dielectric layer using the data on the switching parameters of the system. It is shown that the increase of the coercive field with increasing relative thickness of the dielectric layer, which was considered as an important sign of the presence of the dielectric layer, is not a real property of the sandwich structure but rather an artifact of the approximations which were used in the analysis performed by the previous workers. In fact, E(c) is a decreasing function of the relative thickness of the dielectric layer. (C) 1995 American Institute of Physics.

Spontaneous (zero‐field) relaxor–to–ferroelectric‐phase transition in disordered Pb(Sc1/2Nb1/2)O3

Abstract: Recently, it has been shown that, upon cooling, disordered Pb(Sc1/2Ta1/2)O3 ceramics transform spontaneously from a relaxor state to a ferroelectric state when processed in a manner that suppresses lead vacancies. If lead vacancies are present, the spontaneous ferroelectric transition is suppressed and the ceramics exhibit the usual relaxor behavior in a wide temperature range. It is shown that disordered Pb(Sc1/2Nb1/2)O3 ceramics have a similar nature: When produced in a manner that does not eliminate lead vacancies, they exhibit normal relaxor behavior. However, if stoichiometry is tightly controlled, disordered Pb(Sc1/2Nb1/2)O3 transforms spontaneously (under zero‐bias field) from a relaxor into a normal ferroelectric upon cooling.

Nanoscale visualization and control of ferroelectric domains by atomic force microscopy.

Abstract: The nanoscale visualization and control of domain structure with atomic force microscopy (AFM) in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate is reported. The origin of the domain contrast in the topographic of AFM images is explained by the piezoelectric deformation of the crystal surface in the internal electric field. The domain structure was modified by applying a voltage to the conductive AFM tip. The dynamics of domain growth has been directly observed for the first time with a resolution of 10 nm.

Preparation of Ferroelectric Thin Films of Bismuth Layer Structured Compounds

Abstract: Ferroelectric thin films of bismuth layer structured compounds, SrBi2Ta2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions, were formed onto a sputtered platinum layer on a silicon substrate using spin-on technique and metal-organic decomposition (MOD) method X-ray diffraction (XRD) analysis and some electrical measurements were performed on the prepared thin films XRD results of SrBi2(Ta1-x , Nbx )2O9 films (0?x?1) showed that niobium ions substitute for tantalum ions in an arbitrary ratio without any change of the layer structure and lattice constants Furthermore, XRD results of SrBi2x Ta2O9 films (0?x?15) indicated that the formation of the bismuth layer structure does not always require an accurate bismuth content The layer structure was formed above 50% of the stoichiometric bismuth content in the general formula SrBi2(Ta1-x , Nbx )2O9 films with various Ta/Nb ratios have large enough remanent polarization for nonvolatile memory application and have shown high fatigue resistance against 1011 cycles of full switching of the remanent polarization Mixture films of the three compounds were also investigated

Long-time relaxation of the dielectric response in lead magnoniobate

Abstract: We measured the time dependencies of the dielectric permittivity of a single crystal lead magnoniobate in the zero-field\char21{}cooled regime. The logarithmic decay of the dielectric response was observed in the glassy phase. We measured the time $\ensuremath{\tau}$ from the moment of the field application for the phase transition from the glasslike to the field-induced ferroelectric state to take place, at temperatures below 220 K. The transition is accompanied by the emerging of the even harmonics of the permittivity. It is shown that $\mathrm{ln}\ensuremath{\tau}$ depends linearly on both the inverse temperature and the inverse applied field strength.

Pulsed laser ablation synthesis and characterization of layered pt/srbi2ta2o9/pt ferroelectric capacitors with practically no polarization fatigue

Abstract: Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi2Ta2O9 layered ferroelectric thin films on platinized silicon substrates. Top electrodes were produced by dc magnetron sputter deposition to fabricate capacitors for electrical tests. The polarization electric field hysteresis loops showed saturation in the 2–4 V range with a coercive field of 25 kV/cm. The capacitors showed practically no polarization fatigue up to 1011 switching cycles. The resistivity of the SrBi2Ta2O9 for a coercive field of 100 kV/cm was approximately 2×1011 Ω cm. Retention and imprint characteristics of these capacitors showed no degradation as a function of cumulative waiting times.

Science and technology of electroceramic thin films

Abstract: Preface. Pulsed Laser Ablation-Deposition and Characterization of Ferroelectric Metal Oxide Heterostructures R. Ramesh, O. Auciello, V.G. Keramidas, R. Dat. Low Energy Ion Bombardment Induced Effects in Multi-Component Electroceramic Thin Films S.B. Krupanidhi. Growth and Properties of Pb(Mg1/3Nb2/3)O3 - PbTiO3 and Pb(Zr,Ti)O3 Thin Films by Pulsed Laser Deposition A. Safari, C. Tantigate, J. Lee. Wavelength Dependence in Pulsed Laser Deposition of ZnO Thin Films D. Craciun, V. Craciun. Organometallic Chemical Vapor Deposition of Lead Zirconate Titanate M. de Keijser, P.J. van Veldhoven, G.J.M. Dormans. Alkoxide Precursors for Ferroelectric Thin Films M.I. Yanovskaya, N.Ya. Turva, L.I. Solov'Yova. Deposition of Undoped and Doped Pb (Mg,Nb)O3 - PbTiO3, PbZrxTi1-xO3, Alkaline Earth Titanate and Layered Perovskite Thin Films on Pt and Conductive Oxide Electrodes by Spin - On Processing: Correlation of Growth and Electrical Properties M. Klee, U. Mackens, J. Pankert, W. Brand, W. Klee. Relationships between Ferroelectric 90 Degrees Domain Formation and Electrical Properties of Chemically Prepared Pb(Zr,Ti)O3 Thin Films B.A. Tuttle, T.J. Garino, J.A. Voigt, T.J. Headley, D. Dimos, M.O. Eatough. Characterization of Sol-Gel Pb(ZrxTi1-x)O3 Thin Film Capacitors with Hybrid (Pt,RuO2) Electrodes H.N. Al-Shareef, O. Auciello, A.I. Kingon. Organically Modified Sol-Gel Precursors for Ferroelectric Deposition by Spin Coating P. Gaucher, J. Hector, J.C. Kurfiss. Preparation and Properties of Calcium Modified Lead Titanate Thin Films M.L. Calcada, F. Carmona, R. Sirera, B. Jimenez. Microstructure of Lead Titanate-Based Thin Films L. Pardo, J. Ricote, M.L. Calzada. Stoichiometry and Phase Structure of Sol-Gel Derived PZT-Based Thin Films M. Kosec, Y. Huang, E. Sato, A. Bell, N. Setter, G. Dra i , S. Bernik, T. Beltram. Liquid Phase Epitaxy of Na1-yKyTa1-xNbxO3 on KTaO3 Substrates Z. Sitar, R. Gutmann, P. Gunter. Pulse Switching Characterization of Ferroelectric Thin Films P.K. Larsen, R. Cuppens, G.J.M. Dormans. Polarization, Conduction, and Breakdown in Non-Ferroelectric Perovskite Thin Films R. Waser. Anomalous Logarithmic Dependencies in CD.C. Breakdown of Ferroelectric Thin Films J.F. Scott. The Shape of the Hysteresis Curve of Ferroelectric Single Crystals and Ceramics G. Arlt. Fast Transient Measurements on Electroceramic Thin Films G.W. Dietz, M. Schumacher, R. Waser. The Influence of Dopants on the Leakage Current in PZT Thin-Film Ferroelectric Capacitors D.J. Wouters, G. Willems, G. Groeseneken, H.E. Maes, K. Brooks, R. Klissurska. Photo-Induced Storage and Imprinting in (Pb,La)(Zr,Ti)O3 Thin Films D. Dimos, W.L. Warren, B.A. Tuttle. Depletion, Depolarizing Effects and Switching in Ferroelectric Thin Films A.K. Tagantsev, M. Landivar, E. Colla, K.G. Brooks, N. Setter. Nonstoichiometry, Defects, and Charge Transport in PZT M.V. Raymond, D.M. Smyth. X-Ray Diffraction Line Profile Analysis of ZnO Thin Films Deposited on Al-SiO2-Si Substrates P. Sutta, Q. Jackuliak, V. Tvarozec, I. Novotny. Electron Emission from Ferroelectrics H. Gundel. Integration of Ferroelectric Thin Films for Memory Applications H. Achard, H. Mace. Processing and Device Issues of High Permittivity Materials from Drams B.E. Gnade, S.R. Summerfelt, D

Polarization suppression in Pb(Zr,Ti)O3 thin films

Abstract: Switchable polarization can be suppressed in Pb(Zr,Ti)O3 thin films by optical, thermal, electrical, and reducing processes. The optical suppression effect occurs by biasing the ferroelectric near the switching threshold and illuminating the material with band gap light; the thermal suppression effect occurs by biasing the ferroelectric near the switching threshold and heating the material to ≊100 °C. The electrically induced suppression effect, known as electrical fatigue, occurs by subjecting the ferroelectric capacitor to repeated polarization reversals. We find that the suppressed polarization in these three cases can be restored to essentially its initial polarization value by creating electronic charge carriers in the ferroelectric. This strongly suggests that all three forms of degradation largely involve locking domains by electronic charge trapping at domain boundaries. The fourth form of polarization suppression, a reducing treatment, was obtained by annealing the crystallized PZT films at 400 °C in nitrogen. The suppressed polarization could not be restored by injecting electronic charge into the reduced films, indicating that the mechanism for polarization suppression is different. In this case, it appears as though ionic defects, such as oxygen vacancies, are responsible for locking the domains, and hence, suppressing the polarization.

Stresses in pt/pb(zr,ti)o3/pt thin-film stacks for integrated ferroelectric capacitors

Abstract: A study of the stresses in a ferroelectric capacitor stack deposited on an oxidized silicon substrate is presented. The capacitor stack was prepared with sputtered Pt bottom and top electrodes and a ferroelectric film of composition PbZrxTi1−xO3 (PZT) with x≊0.5 which was deposited using a modified sol‐gel technique. The stresses were determined by the changes in the radius of curvature of the wafer following the deposition steps, during and after annealing treatments, and after etching steps in which the top electrode, the PZT film, and the bottom electrode were successively removed. The largest stress effects are found in the Pt electrodes which are deposited under conditions giving an intrinsic compressive stress. An annealing treatment exceeding 500 °C changed the stress of the bottom electrode from ≊−750 MPa (compressive) to a large tensile stress (≊1 GPa). This stress is largely thermal and is caused by the differences in thermal‐expansion coefficients of the Pt film and the Si substrate. The stress of the PZT film is numerically relatively small (below ≊200 Mpa) and it is found to be of both thermal and intrinsic origin. The deposition and annealing of the top electrode has a profound influence on the stress of the PZT film as well as on the electrical properties. The stress behavior of the as‐deposited PZT film shows a poling direction mainly in the plane of the substrate. An annealing of the complete capacitor stack changes the poling direction of the ferroelectric film to be perpendicular to the substrate. This explains the observed electrical switching properties of as‐prepared as well as annealed ferroelectric capacitors.

Characteristics of Bismuth Layered SrBi2Ta2O9 Thin-Film Capacitors and Comparison with Pb(Zr, Ti)O3

Abstract: We have developed the series of thin-film bismuth layer structured ferroelectric (BLSF) materials such as SrBi2Ta2O9, SrBi2Nb2O9, SrBi4Ti4O15 and their solid solutions using metallo-organic-decomposition (MOD) spin-on coating techniques. We found that SrBi2Ta2O9 is one of the best potential candidate materials for ferroelectric nonvolatile memories. The SrBi2Ta2O9 thin-film capacitor had the remanent polarization (P r+-P r-) of 20 µ C/cm2, coercive field of 35 kV/cm and dielectric constant of 250. SrBi2Ta2O9 thin film on platinum electrode has fatigue-free characteristics for up to 2×1011 cycles without requiring any complicated electrode system such as conductive oxide. Moreover, SrBi2Ta2O9 thin film has many advantages, e.g., high signal/noise ratio of 8 at 1.2 V, low-voltage operation at as low as 1 V, long data-retention, little surface effect, superior imprint properties and low leakage current. We considered that these advantages are due to (1) less space charge and (2) the inherent domain motion.

Preparation of (100)‐oriented metallic LaNiO3 thin films on Si substrates by radio frequency magnetron sputtering for the growth of textured Pb(Zr0.53Ti0.47)O3

Abstract: Highly (100)‐oriented LaNiO3(LNO) thin films were grown on Si, SiO2/Si, Pt/SiSiO2/Si, as well as glass substrates by rf magnetron sputtering deposition at substrate temperatures ranging from 150 to 500 °C. As‐deposited LNO films are metallic; those prepared at substrate temperature ∼150–250 °C have a resistivity of 0.4–0.5 mΩ cm and can be used as the bottom electrode for the fabrication of integrated ferroelectric capacitors on Si. A subsequent deposition of sol‐gel derived Pb(Zr0.53Ti0.47)O3 (PZT) thin film on the LNO‐coated substrate was also found to have a significant (100)‐ and (001)‐oriented texture. The ferroelectric capacitor fabricated from these films displays a good P–E hysteresis characteristic.

Electric field induced cracking in ferroelectric ceramics

Abstract: Ferroelectric ceramics are susceptible to fracture under high magnitude cyclic electric field. Flaws concentrate the electric field, inducing a large incompatible strain, and thereby a large stress. Stable growth of cracks with either conducting or insulating interiors is observed in 8/65/35 lanthanum lead zirconate titanate samples. Indentations on the electroded surface are filled with distilled water or a water-salt solution. Under cyclic electric field, tree like damage grows from the indented electrode. Indentations on the surfaces 90° to the electrodes are filled with silicone oil. This results in stable crack growth perpendicular to the cyclic electric field. Nonlinear fracture models are presented for both conducting and insulating cracks. Tensile stress intensity factors are predicted for both cases.

Electrical properties’ maxima in thin films of the lead zirconate–lead titanate solid solution system

Abstract: The piezoelectric strain coefficients have been measured as a function of composition for films in the PbZrO3–PbTiO3 (PZT) solid solution system, using a double‐beam laser interferometry technique. This compositional dependence of piezoelectric, and the associated dielectric and ferroelectric properties for films 1 μm in thickness with varying Zr/Ti ratio, deposited on platinized silicon substrates using a modified sol‐gel route, corresponds to data reported for undoped PZT ceramics with respect to the effective morphotropic phase boundary composition. Films with composition near the morphotropic phase boundary, Pb(Zr0.52Ti0.48)O3, show enhanced values of the longitudinal piezoelectric coefficient, 194 pC/N; dielectric permittivity, 1310; and remanent polarization, 36 μC/cm2.

Domain configurations due to multiple misfit relaxation mechanisms in epitaxial ferroelectric thin films. III. Interfacial defects and domain misorientations

Abstract: Interfacial defect theory is applied to the epitaxial ferroelectric system consisting of a tetragonal ferroelectric such as BaTiO3 or PbTiO3 grown onto a cubic (001) substrate. The interfacial defects that result from the diffusionless paraelectric to ferroelectric (PE→FE) phase transition are treated under the constraint that no misfit dislocations are generated during or as a result of the transition. The domain pattern develops to provide strain relief in the film. The interfacial defects for the ...c/a1/c/a1... domain pattern include coherency edge dislocations and coherency wedge disclinations. Interfacial defects for the ...a1/a2/a1/a2... domain pattern include coherency edge and screw dislocations. Far‐field strain states for both domain patterns can be predicted from the interfacial defect content. From the twinning geometry, general expressions are derived for the far‐field rotations of the crystal axes of individual domains for the ...a1/c/a1/c... and the ...a1/a2/a1/a2... domain pattern. The ge...

Ferroelectric properties in epitaxially grown BaxSr1−xTiO3 thin films

Abstract: Induced ferroelectricity was observed in epitaxially grown BaxSr1−xTiO3 (BST) thin films with thicknesses of about 220 nm The BST films with various Ba content were deposited at 600 °C on Pt/MgO substrates, by radio frequency magnetron sputtering with double targets, BaTiO3 and SrTiO3 The epitaxial growth of the BST films was confirmed with x‐ray‐diffraction and reflection high‐energy electron‐diffraction analyses The D–E hysteresis curve and the Curie temperature shift confirmed the BST films with Ba content x≥044 had ferroelectricity at room temperature The mechanism of the ferroelectricity appearance was discussed in relation to the elongation of the c axis in the thickness direction, caused by lattice mismatch between Pt and BST

Tuneable microwave devices including fringe effect capacitor incorporating ferroelectric films

Abstract: The present invention relates to a tuneable fringe effect capacitor for conducting radio frequency energy. The capacitor includes a thin film of ferroelectric material, a pair of films of a conductive material deposited on the ferroelectric film with a gap between the films, and a substrate for the ferroelectric material and the conductive films. The capacitance value across the gap is varied by applying a voltage to the ferroelectric material and thereby altering the dielectric constant of the ferroelectric material.

Ceramic ferroelectric composite material-BSTO-magnesium based compound

Abstract: Ceramic ferroelectric composite material-BSTO-Magnesia based compounds hag a low dielectric constant, low loss tangent and high tunability are disclosed The composite material comprises Barium Strontium Titanate (BSTO) and a magnesia compound selected from the group consisting, MgZrO 3 , MgAl 2 O 4 , and MgTiO 3 The preferred composite is represented by Ba 1-x Sr x TiO 3 -magnesia compound, wherein x is greater than 000, but less than or equal to 075, and wherein the percent weight ratio between BSTO and magnesia compound ranges from approximately 99%-40% and 1%-60%, respectively The novel materials possess superior electronic properties, and they may be employed in various antenna systems

Ferroelectric fatigue in perovskite oxides

Abstract: We find that the reduction of the switchable polarization in BaTiO3 crystals via repeated polarization reversals (fatigue) is accompanied by the trapping of electronic charge and atomic scale distortions in the perovskite oxygen octahedron. The distortions are proposed to involve oxygen vacancies.

Thin film ferroelectric composites and method of making

Abstract: A thin film composite material comprises barium strontium titanate represented as Ba1-x Srx TiO3 wherein x is greater than 0.0 but less than or equal to 0.75 and a magnesia-based compound such as MgZrO3, MgTiO3, MgAl2 O4 and mixtures thereof. The thin film ferroelectric composite is made using pulsed laser deposition and exhibits high tunability, low loss and a low dielectric constant.

Epitaxial all‐perovskite ferroelectric field effect transistor with a memory retention

Abstract: All‐perovskite ferroelectric field effect transistors (FET) are proposed, and switching behaviors of the prototype devices having a (Pb,La)(Zr,Ti)O3 as a gate insulator and a La1.99Sr0.01CuO4 as a channel layer were demonstrated. Marked improvements in device performances were obtained as compared with the previous ferroelectric FETs. Namely, the present device was written and erased at an operating voltage of 7 V with a pulse width of less than 1 ms, yielding resistance modulation up to about 10% and retaining its memory for more than 10 days at room temperature. Examinations show that the switching speed was limited by a delay constant and can therefore be improved up to 1 μs, and that the memory retention may not be limited by an intrinsic ferroelectric instability as previously suggested.