Effective dielectric response of polymer composites with ceramic coated silver flakes

High permittivity polymer composites were prepared using Bisphenol A epoxy resin and low loss alumina (Al₂O₃) coated silver (Ag) flakes for embedded passives. The uniformity and thickness of the Al₂O₃ layer were studied using both scanning and transmission electron microscopy (SEM and TEM). SEM was also used to investigate the morphology of the composites and the particle distribution. The dielectric properties of the composites were measured as a function of frequency and temperature. The composites showed a high relative permittivity of 370 with a low loss tangent of 0.07 at 1 MHz and a temperature coefficient of permittivity ~160 ppm/K.     

Dielectric properties of BaTiO<Subscript>3</Subscript>/epoxy composites by lamination process for embedded capacitor application

Because of the fabricability of polymer and excellent dielectric properties of ceramics, ceramic-polymer composites have been investigated widely for embedded capacitors which can improve electric performance greatly. In order to obtain further application of composite, the embedded capacitors with three-layer sandwich structure containing the BaTiO₃/epoxy composites as dielectric layer and copper foil as electrodes were fabricated. The dielectric properties are improved by preventing the defect in dielectric layer through lamination process. Our results show that the capacitors exhibit high dielectric permittivity (ε = 20), low dielectric loss (0.01) at 10³ Hz from 40 to 100 °C and high breakdown strength (24 kV/mm), which indicate that the lamination is a promising process for embedded capacitor fabrication and BaTiO₃/epoxy composites have potential for high-performance embedded capacitors application in field of microelectronics.     

Ba(Zn1/3Ta2/3)O3 ceramics reinforced high density polyethylene for microwave applications

The effect of Ba(Zn_1/3Ta_2/3)O₃ (BZT) ceramic filler on the dielectric, mechanical and thermal properties of high density polyethylene (HDPE) matrix have been investigated. The dispersion of BZT particles in the matrix was varied up to 0.45 volume fraction (V_f)_. The SEM images confirmed the increase in connectivity between the filler particles with the increase in filler loading. All the composites showed excellent densification (>99 %) with relatively low moisture absorption (<0.04 wt%). The dielectric properties of the composites were investigated at 1 MHz, 5 GHz and at 10 GHz. The relative permittivity and the dielectric loss were found to increase as a function of BZT loading. Different theoretical models were used to predict the relative permittivity at 10 GHz. Effective medium theory gave the best correlation with the experimental results. An enhancement in the thermal conductivity (TC) and a reduction in the coefficient of linear thermal expansion (CTE) were achieved with filler loading. A slight decrease in the tensile strength was also observed with BZT loading. At 10 GHz, 0.45 V_f BZT reinforced HDPE showed a low relative permittivity (ε_r = 8.2) and a low dielectric loss (tanδ = 1.6 × 10^?3) with good thermal (TC = 1.4 W m^?1 K^?1, CTE = 92 ppm/°C) and mechanical (tensile strength = 18 MPa) properties.     

A General Strategy to Achieve Colossal Permittivity and Low Dielectric Loss Through Constructing Insulator/Semiconductor/Insulator Multilayer Structures

In this work, we propose a route to realize high-performance colossal permittivity (CP) by creating multilayer structures of insulator/semiconductor/insulator. To prove the new concept, we made heavily reduced rutile TiO₂ via annealing route in Ar/H₂ atmosphere. Dielectric studies show that the maximum dielectric permittivity (~?3.0?×?10⁴) of our prepared samples is about 100 times higher than that (~?300) of conventional TiO₂. The minimum dielectric loss is 0.03 (at 10⁴–10⁵ Hz). Furthermore, CP is almost independent of the frequency (100–10⁶ Hz) and the temperature (20–350 K). We suggest that the colossal permittivity is attributed to the high carrier concentration of the inner TiO₂ semiconductor, while the low dielectric loss is due to the presentation of the insulator layer on the surface of TiO₂. The method proposed here can be expanded to other material systems, such as semiconductor Si sandwiched by top and bottom insulator layers of Ga₂O₃.     

Investigations on structural evolution and dielectric characteristics of high performance Bi-based dielectrics

A new system of (Bi_1.5Zn_1−x/3Ti_xNb_1.5−2x/3)O₇ (0 ≤x ≤ 1.5) ceramics have been successfully developed and the dielectric properties have been systematically studied. The results showed the formation of temperature compensation dielectrics over the wide range of Ti concentrations. The incorporation of Ti⁴⁺ into the bismuth zinc niobate ceramics induce the decrease of lattice constant linear while remaining cubic pyrochlore phase. The IR spectra confirm the formation of pyrochlore structure and give information about the distribution of ions between the A and B sites. It has been found that the effect of Ti substitution on dielectric properties of sintered ceramics intensifies with a higher x. The system exhibits the novel high permittivity and low dielectric loss: the permittivity values (?_r) saturate at 160-210, and loss values remain at low values (∼1 × 10⁻⁴). The temperature dependence of permittivity is strongly dependent with the compositions. Dielectric relaxation phenomena have been observed during low temperature. New high frequency and MW materials, differed by Ti content, with temperature compensation and controllable dielectric constant of 150-210 have been developed.     

Mechanical and dielectric properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites were prepared using two types of surface-treated montmorillonite (Closite 30B and Nanomer I28E). Wide angle X-ray scattering showed that all the nanocomposites had an intercalated structure. Improvements in tensile and fracture properties were found. The pure epoxy polymer was very brittle with a fracture energy, G _c, of 131 J m^?2. The addition of the nanoclays significantly increased the value of G _c, up to 240 J m^?2 for 5 wt% C30B. The toughening mechanisms acting in the nanocomposites were identified using scanning electron microscopy as crack deflection and plastic deformation of the epoxy matrix around the clay platelets following debonding. From electrical testing, the permittivity and loss angle of the nanocomposites decreased, and their breakdown strength increased as desired for insulation applications. The breakdown strength of the pure epoxy was found to be 11.7 kV mm^?1, while for a 2 wt% C30B nanocomposite, it increased to 14.7 kV mm^?1. It was concluded that the restriction of chain mobility inhibited electrical polarisation and thus decreased the permittivity and loss angle. The electrical damage zone was analysed using scanning electron microscopy. It was found that the higher resistance-to-surface degradation by partial discharges and the creation of a tortuous electrical path, which delayed the propagation of the electrical tree, were the main factors which improved the breakdown strengths of the nanocomposites.     

Preparation of the LTCC composite ceramics with low permittivity

In this work, the LTCC composite ceramics containing ??-alumina and quartz based on the binary system BaO?CB₂O₃ were prepared by traditional solid-state preparation process at a sintering temperature of 900 °C. Sintering mechanism and physical properties of the LTCC composite ceramics are investigated and discussed in detail in terms of their mineral phase composition. The results indicate that, by the chemical combination of barium hydroxide octahydrate and an aqueous solution of boric acid, a barium borate phase can be formed form the binary system BaO?CB₂O₃ and consequently supply a liquid sintering aid for the fabrication of LTCC composite ceramics at a sintering temperature of 900 °C. The introduction of ??-alumina to the binary system BaO?CB₂O₃ can improve the sintering behavior whereas the presence of quartz in the composite ceramics is important to achieve low permittivity. By the combination of ??-alumina, quartz and BaO?CB₂O₃ composition, the dense LTCC composite ceramics, which is characterized by excellent dielectric properties (permittivity: 3.56; 4.83; dielectric loss: 3 × 10^?4; 4 × 10^?4), can be fabricated availably.     

Dielectric properties of Sr3CuNb2O9 perovskite ceramics

The dielectric constant ? and loss tangent tanδ of Sr₃CuNb₂O₉ perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 10⁶ Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (? ? 10) and dielectric losses (tanδ ? 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ? ? 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr₃CuNb₂O₉ ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.     

Dielectric nonlinearity and electrical properties of K0.5Na0.5NbO3–SrTiO3 relaxor ferroelectrics

K_0.5Na_0.5NbO₃–xSrTiO₃(x = 0, 0.1 and 0.2) ceramics were prepared using the solid-state method. The phase transition behaviors, electrical properties, and electric field-induced dielectric nonlinearity behaviors were investigated as a function of the SrTiO₃ content. The electrical properties of the investigated compositions exhibited a significant dependence on the content of SrTiO₃. Doped content more than x = 0.1 induced a relaxor transformation, while the dielectric loss decreased quickly. In addition, an “extrinsic” polarization contributed to the dielectric nonlinearity behavior of the composition x = 0.1 with the polar nanoregions and domain-wall motions, by means of the multipolarization-mechanism model fittings of the electric field dependence of the dielectric permittivity. The dielectric tunability and loss angle tangent of the composition x = 0.1 were 32.6 % and 0.028, respectively.     

Low-temperature synthesis of CaCu3Ti4O12 powders, ceramics and thin films via an organic solution

The giant-dielectric-constant material CaCu₃Ti₄O₁₂ (CCTO) was synthesized via an organic solution containing stoichiometric amounts of the metal cations, which is done at lower temperature and shorter reaction time than the conventional solid-state reaction. A stable solution was prepared by dissolving calcium nitrate, copper nitrate, and tetrabutyl titanate in grain alcohol. CCTO powders, ceramics and thin films were synthesized via the solution. The phases, microstructures, and dielectric properties of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and dielectric spectroscopy. XRD results identify both samples as single phase CCTO. The CCTO ceramics has a low-frequency permittivity of 3.5 × 10⁴. The CCTO thin films has a low-frequency permittivity of 3.1 × 10⁴. Both the CCTO ceramics and CCTO thin films exhibit two dielectric relaxations at room temperature. The low leakage current density of CCTO thin films shows that it is suitable for memory device applications.     

Low dielectric permittivity and high thermal stability composites based on crosslinkable poly (arylene ether nitrile) and hollow glass microsphere

Crosslinkable poly (arylene ether nitrile)/hollow glass microsphere (PEN/HGM) composites with relative low dielectric permittivity and high thermal stability were prepared by a solution mixing and thermal compression method. For achieving this purpose, HGM were tight embedded in network, which were formed by crosslinking reaction of PEN end-capped with phthalonitrile. Compared to pure PEN, the dielectric constant of the resulting composite with 15 wt% of HGM reduced from 4.1 to 2.7 at 100 kHz, and the dielectric loss decreased from 2.0 × 10^?2 to 0.8 × 10^?2 at 100 kHz. Furthermore, the as-prepared composites showed significant enhancement in glass transition temperature (increased by 64 °C) and onset thermal degradation temperature (increased by 41 °C). Therefore, such composites were expected to find their applications area such as integrated circuit where needs low dielectric constant, low dielectric loss and high thermal stability.     

Tensile,dielectric, and thermal properties of epoxy composites filled with silica,mica, and calcium carbonate

The minerals silica, mica, and calcium carbonate (CaCO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler loading and type on the morphology, tensile, dielectric, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin films with 20 vol% filler loading showed good dielectric properties, thermal conductivity, and thermal stability. However, the tensile properties of the thin films were reduced as the filler loading was increased due to brittleness. Dielectric constant and dielectric loss of epoxy/inorganic composite films generally increased with increasing mineral filler loading. Meanwhile, the presence of mineral filler improved the thermal stability of the thin film composites. The highest dielectric constant of 5.75 with 20 vol% filler loading at a frequency of 1 MHz was exhibited by the epoxy/CaCO₃ composite, followed by epoxy/mica and epoxy/silica. Therefore, the epoxy/CaCO₃ composite is the most potential candidate for capacitor application. Moreover, precipitated CaCO₃ provided better tensile properties and slightly improved the dielectric properties compared with mineral CaCO₃.     

Hydrothermal Synthesis,Structural and Electrical Properties of Antimony (Sb3+) Substituted Nickel Ferrites

Antimony (Sb³⁺) doped nickel ferrites have been synthesized by hydrothermal route using an autoclave at 160 ^°C for 12 hours. Pure spinel phase NiSb _x Fe_2?x O₄ (x=0.0 to 0.1) with step increment of 0.035 has been prepared by sintering the precursor samples at 500 ^°C. Structural studies have been performed using X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Lattice parameter and X-ray density found to increase with increase in the antimony concentration. Average crystallite size lies in the range of 14 to 24 nm?±?2 nm. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) have been used to characterize the morphology and sizes of nanoparticles. Electrical properties were analyzed by measuring DC-electrical resistivity, complex dielectric permittivity, AC conductivity and complex electrical modulus analysis. DC resistivity of nickel ferrites decreases due to the substitution of antimony from 6.7×10⁸ to 3.4×10⁷ Ω-cm. Dielectric permittivity and losses were studied in the frequency range of 20 Hz–5 MHz and found to increase due to addition of Sb³⁺ in nickel nanoferrites at room temperature. High dielectric permittivity and conductivity made this material a compatible option for single-layered and multilayered chip inductors.     

Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites

Titanium oxide TiO₂/epoxy and TiO₂ with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO₂ and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO₂/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO₂-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO₂-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at ?14.5 and ?1.3 dB, respectively. The flexural and tensile strength of TiO₂-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO₂-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO₂ nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.     

Bi1.5Zn1.0Nb1.5O7 thin films deposited at low temperature and post-annealed for crystallization

Near-stoichiometric Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si (100) substrates at 400 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The as-deposited BZN thin films were post-annealed at 700 °C for 30 min in situ vacuum chamber (in situ) and in oxygen ambient oven (ex situ). The crystallinity, microstructure and electrical properties of BZN thin films were investigated. The X-ray diffractometer results indicate that BZN thin films deposited at 400 °C are amorphous in nature and the post-annealed thin films exhibit a cubic pyrochlore structure. The as-deposited BZN thin films show permittivity of 68 and loss tangent of 0.0011 at 10 kHz, respectively. After a post-annealing at 700 °C for 30 min, the dielectric properties of thin films are significantly improved. Permittivity and loss tangent of the in situ annealed films are 127 and 0.005 at 10 kHz, respectively. And the films post-annealed in O₂ oven show the largest permittivity of 170 and tangent of 0.006. The improved dielectric properties can attribute to the crystallization of thin films. BZN thin films deposited at low temperature and crystallized at high temperature show the dielectric tunability without an electric breakdown to the maximum measurement bias voltage. And BZN thin films also show the excellent leakage current properties.     

Sandwiched epoxy–alumina composites with synergistically enhanced thermal conductivity and breakdown strength

Development of polymer-based composites with simultaneously high thermal conductivity and breakdown strength has attracted considerable attentions owing to their important applications in both electronic and electric industries. In this study, we successfully design novel epoxy-based composites with nano-Al₂O₃/epoxy composite layer sandwiched between micro-Al₂O₃/epoxy composite layers, which show synergistically and significantly enhanced thermal conductivity and breakdown strength. Compared with the traditional composites, the bottleneck that both thermal conductivity and breakdown strength cannot be simultaneously enhanced can be overcome successfully. An optimized sandwiched alumina–epoxy composite with 70 wt% micro-Al₂O₃ fillers in the outer layers and 3 wt% nano-Al₂O₃ in the middle layer simultaneously displays a high thermal conductivity of 0.447 W m^?1 K^?1 (2.4 times of that of epoxy) and a high breakdown strength of 68.50 kV mm^?1, which is 6.3 % higher than that of neat epoxy (64.45 kV mm^?1). The experimental results on the thermal conductivity of multi-layered alumina–epoxy composites were in well accordance with the theoretical values predicted from the series conduction model. This novel technique simultaneously improves thermal conductivity and breakdown strength, which is of critical importance for design of perspective composites for electronic and electric equipments.     

All-organic PANI–DBSA/PVDF dielectric composites with unique electrical properties

Novel all-organic polymer high-dielectric permittivity composites of polyaniline (PANI)/poly (vinylidene fluoride) (PVDF) were prepared by solution method and their dielectric and electric properties were studied over the wide ranges of temperatures and frequencies. To improve the interface bonding between two polymers, dodecylbenzenesulfonic acid (DBSA), a bulky molecule containing a polar head and a long non-polar chain was used both as a surfactant and as dopant in polyaniline (PANI) synthesis. Synthesized conducting PANI–DBSA particles were dispersed in poly(vinylidene fluoride) (PVDF) matrix to form an all-organic composite with different PANI–DBSA concentrations. Near the percolation threshold, the dielectric permittivity of the composites at 100 Hz frequency and room temperature was as high as 170, while the dielectric loss tangent value was as low as 0.9. Like typical percolation system, composites experienced high dielectric permittivity at low filler concentrations. However, their dielectric loss tangent was low enough to match with non-percolative ceramic filler-based polymer composites. Maximum electrical conductivity at 24 wt% of PANI–DBSA was mere 10^?6 S/cm, a remarkably low value for percolative-type composites. Increase in the dielectric permittivity of the composites with increase in temperature from 25 to 115 °C for different PANI–DBSA concentrations was always in the same range of 50–60 %. However, the degree of increase in the electrical conductivity with the temperature was more prominent at low filler concentrations compared with high filler concentrations. Distinct electrical and their unique thermal dependence were attributed to an improved interface between the filler and the polymer matrix.     

Dense PLZT films grown on nickel substrates by PVP-modified sol–gel method

We have successfully grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on base metal foils by chemical solution deposition using sol–gel solutions containing polyvinylpyrrolidone. Under zero-bias field, we measured a dielectric constant of ≈820 and dielectric loss of ≈0.06 at room temperature, and a dielectric constant of ≈1250 and dielectric loss of ≈0.03 at 150 °C. In addition, leakage current density of ≈1.5 × 10^?8 A/cm², remanent polarization of ≈11.2 μC/cm², and coercive field of ≈40.6 kV/cm were measured at room temperature on a ≈3-μm-thick PLZT film grown on LaNiO₃-buffered nickel substrate. Finally, energy density ≈25 J/cm³ was measured from the P–E hysteresis loop at an applied field of 2 × 10⁶ V/cm.     

Butterfly-shaped multiferroic BiFeO3@BaTiO3 core–shell nanotubes: the interesting structural, multiferroic, and optical properties

Highly pure butterfly-shaped BiFeO₃@BaTiO₃ nanotubes have been synthesized through a sol–gel method. An obvious ferromagnetic behavior was obtained at room temperature, with a large coercive field (5,403 Oe) and high Mr/Ms value (0.52). The dielectric permittivity of BiFeO₃@BaTiO₃ nanotubes was found to be 1919, which is much higher than that of pure BFO nanostructure. The dielectric loss of BiFeO₃@BaTiO₃ nanotubes is low in the frequency range from 10 Hz to 1 MHz. The maximum magnetoelectric coefficient of BiFeO₃@BaTiO₃ nanotube is 0.272 μV/cm Oe. Moreover, the BiFeO₃@BaTiO₃ nanotubes have exhibited a better ferroelectric property with a large band gap of 3.2 eV which demonstrates the core–shell nanostructure.     

Doping behaviors of yttrium,zinc and gallium in BaTiO3 ceramics for AC capacitor application

The doping behaviors of yttrium, zinc and gallium and their effects on the dielectric properties and microstructures of BaTiO₃ were investigated. Y³⁺ dissolved in the lattice of BaTiO₃, replacing both Ba²⁺ site and Ti⁴⁺ site; while Zn²⁺ and Ga³⁺ tended to occupy Ti⁴⁺ site. Compared with Y₂O₃ and Ga₂O₃, ZnO suppressed grain growth of BaTiO₃ more effectively and promoted greater uniformity of grains, thus reducing the dielectric loss. The addition of Ga₂O₃ inhibited the appearance of second phase Y₂Ti₂O₇ and enhanced the sinterability, which was ascribed to the compensation mechanism and synergistic effect. Proper amount of Y₂O₃, Ga₂O₃ and ZnO significantly improved the dielectric temperature characteristics due to the formation of the core–shell structure in the codoped BaTiO₃ ceramics. High performance dielectrics with ε_r of 2,690, tanδ of 1.0 % (at 1 kHz), and alternating current breakdown voltage E > 3.73 kV/mm, were achieved.