Synthesis and characterization of borosilicate glass/β-spodumene/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites with low CTE value for LTCC applications

Glass?+?ceramic composites based on low-softening-point borosilicate (BS) glass, β-spodumene and Al₂O₃ were produced in this work. The influence of ceramic filler composition on the microstructure, sintering quality, mechanical properties, thermal properties and dielectric properties of composites were studied. XRD and DSC indicated that both kinds of ceramic filler as well as the BS glass maintained their characteristics after sintering. The addition of β-spodumene would decrease the coefficient of thermal expansion (CTE) value of composites to match with silicon well. The better wetting behavior between β-spodumene and BS glass would lead to better sintering quality, microstructure and dielectric properties for composites containing more β-spodumene. With appropriate Al₂O₃ content, the flexural strength of composites could be enhanced. Composite with 45 wt% BS glass, 30 wt% β-spodumene and 25 wt% Al₂O₃ sintered at 875 °C showed good properties which meet the requirements of low temperature co-fired ceramic applications: dense microstructure with high relative density of 96.27%, proper CTE value of 3.57 ppm/°C, high flexural strength of 156 MPa, low dielectric constant of 6.20 and low dielectric loss of 1.9?×?10^?3.     

Novel X8R-type BaTiO3-based ceramics with a high dielectric constant created by doping nanocomposites with Li–Ti–Si–O

A novel system of temperature-stable Electronic Industries Alliance X8R dielectric materials with high dielectric constants can be obtained by doping BaTiO₃-K_0.5Na_0.5NbO₃ ceramic nanocomposites with 0.7 wt% Li–Ti–Si–O. The dielectric constant is greater than 3,960 at 25 °C, with a dielectric loss lower than 0.8 % and a temperature coefficient of capacitance less than ±12 % from ?55 to 150 °C. The doping increased the degree of tetragonality, grain size, and density, thereby increasing the dielectric constant. We provide additional data on the phase composition, microstructure, and dielectric properties of the doped samples. These materials show high potential for applications in X8R-type multilayer ceramic capacitors.     

Effect of fluxing additive on sintering temperature, microstructure and properties of BaTiO3

Various fluxing materials are added to technical ceramics in an attempt to lower their sintering temperatures and make their processing economical. The effect of 0·3?wt% Li₂CO₃ addition on the phase, microstructure, phase transition temperatures and dielectric properties of BaTiO₃ was investigated in the present study. The addition of 0·3?wt% Li₂CO₃ was observed to lower the optimum sintering temperature by ??200°C with no second phase formation and cause a five-fold reduction in grain size. Rhombohedral-to-orthorhombic and tetragonal-to-cubic phase transitions at the expected temperatures were evident from the Raman spectra, but the orthorhombic-to-tetragonal phase transition was not clearly discernible. The persistence of various phase(s) at higher temperatures in the flux-added materials indicated that the phase transitions occurred relatively slowly. A decrease in dielectric constant of Li₂O-added BaTiO₃ in comparison to pure BaTiO₃ may be due to the diminished dielectric polarizability of Li^?+? in comparison to Ba^2?+?.     

Influence of adsorbed moisture on the properties of cyanate ester/BaTiO3 composites

The effect of moisture adsorbed on BaTiO₃ on the properties of cyanate ester (CE)/BaTiO₃ dielectric composites is examined using undried and dried BaTiO₃ particles. The influence of moisture on the dielectric constant, thermal stability, dynamic mechanical properties, flexural behavior and micro morphology of the composites is investigated. Dielectric constant (ε) and dielectric loss (tan δ) of composites with the dried BaTiO₃ are both higher than composites manufactured with undried filler at the same frequency. The dielectric properties of the dried system are stable over a broader temperature range than the undried composites. Adsorbed moisture causes the initial decomposition temperature and the maximum degradation temperature of the composite to decrease by 27 °C and 15 °C, respectively. By removing the moisture from BaTiO₃, the CE/BaTiO₃ composite exhibits a lower modulus (E′), higher strength, higher flexural elongation and a dramatically increased glass transition temperature (T_g).     

Effect of Bi2O3 doping on the dielectric properties of medium-temperature sintering BaTiO3-based X8R ceramics

Medium-temperature sintering X8R ceramics were fabricated based on BaTiO₃-based ceramics with Bi₂O₃ additives. The effects of sintering aids Bi₂O₃ on crystalline structure and electrical properties of BaTiO₃-based ceramics were investigated. The sinterability of BaTiO₃ ceramics was significantly improved by adding Bi₂O₃, whose densification sintering temperature reduced from 1,260 to 1,130 °C. However, the dielectric constant (ε) of BaTiO₃-based ceramics doped with Bi₂O₃ was decreased dramatically. Both low ε phase Bi₄Ti₃O₁₂ and the decrease of the tetragonality (c/a ratio), which are demonstrated by XRD pattern, are resulted in the decrease of ε. The ε of samples doped with 5.5 wt% Bi₂O₃ was higher than the other doped samples. The substitution of Bi³⁺ for the Ba²⁺ in BaTiO₃ resulted in the increase of electrovalence (from +2 to +3) of A-site ion, so the attractive force between A and B (Ti⁴⁺) sites becomes stronger. Thus Ti⁴⁺’s polarization enhances, then ε was increased to some extent. The X8R BaTiO₃-based ceramics could be sintered at as low as 1,130 °C by doping 5.5 wt% Bi₂O₃ additives into the BaTiO₃-based ceramics, with a ε greater than 2,430 at 25 °C, dielectric loss lower than 1.3 % and temperature coefficient of capacitance <±15 % (?55–150 °C).     

Dielectric behaviour of barium titanate-polyvinylidene fluoride composites

The dielectric behaviour of composites of barium titanate (BaTiO₃) and polyvinylidene fluoride (PVDF) has been studied by changing the weight fraction of BaTiO₃. The dielectric behaviour of the composites has a significant influence of PVDF up to 50wt% BaTiO₃ in the composite, but this effect is insignificant at higher weight fractions of BaTiO₃. X-ray diffraction studies on composites are also reported to correlate the observed dielectric changes with the corresponding structural changes.     

Effect of spark plasma sintering temperature on the phase equilibria and dielectric properties of BaTi2O5 ceramics

The effect of sintering temperature (ranging from 1055 to 1200 °C) on the phase ingredient and dielectric property of the nominal BaTi₂O₅ ceramics (starting with the Ba/Ti of 1:2) fabricated by a spark plasma sintering method were systematically studied. At the first stage, BaTi₂O₅ component was enhanced in the sintering temperature range of 1055–1120 °C; it turned out to be the dominant phase. For these BaTi₂O₅ phase dominated ceramics, the Curie temperature T _c rised on increasing the sintering temperature and saturated around 440 °C with the maximum dielectric constant of 500. Further increasing the sintering temperature, the decomposition of the obtained BaTi₂O₅ into BaTiO₃ extensively happened; the ceramics turned to be the BaTi₂O₅ and BaTiO₃ coexisting state. These ceramics can be characterized by two dielectric anomalies. One at ~420 °C stood for the phase transition of BaTi₂O₅ while the other at ~150 °C stood for the transition of BaTiO₃, which is exceptionally high as the normal BaTiO₃ ceramics. Further increasing the sintering temperature (until 1200 °C) would dramatically enhance the BaTiO₃ phase; the ceramics showed T _c at 130 °C with the maximum dielectric constant of 1800.     

Investigation of Li<Subscript>2</Subscript>Zn<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>-based temperature stable dielectric ceramics for LTCC applications

A low temperature co-fired ceramic (LTCC) was fabricated at 910 °C /2 h from the powder mixture of Li₂Zn₃Ti₄O₁₂, TiO₂ and a B₂O₃–La₂O₃–MgO–TiO₂ glass (BLMT), and the influence of TiO₂ on microstructure and dielectric properties of the composite was investigated in the composition range (wt%) of 20BLMT–(80???x)Li₂Zn₃Ti₄O₁₂–xTiO₂ (x?=?0, 2.5, 5, 7.5, 9 and 10). The results showed that all samples consisted of Li₂Zn₃Ti₄O₁₂, TiO₂, LaBO₃ and LaMgB₅O₁₀ phase. And LaBO₃, LaMgB₅O₁₀ and a small amounts of TiO₂ were crystallized from BLMT glass during sintering process. As x increases, dielectric constant and temperature coefficient of resonance frequency of the composites demonstrated gradually increase, whereas the quality factor of the sample of x?=?0 wt% was about 41,500 GHz and the ones maintained stable at a high level of 49,000–51,000 GHz for other samples. The composite with x?=?9 wt% had an optimal microwave dielectric properties with the dielectric constant of 20.2, quality factor of 50,000 GHz and temperature coefficient of resonant frequency of ??0.33 ppm/°C.     

Influence of coupling agent on microcosmic morphology and dielectric properties of energy-storage nanocomposite

A series of PVDF-based composite materials with 20 % volume concentrations of nano-sized BaTiO₃ fillers were prepared and studied by solutions-casting. The samples were added with different contents of KH550 as coupling agent. The four main dielectric parameters: dielectric constant, dielectric loss tangent, dielectric breakdown strength and resistivity under high electrical field, were tested. And the energy-storage densities of the samples were also calculated. The results showed that the nanocomposites with 1.0 wt% of KH550 exhibited the appropriate dielectric constant, loss tangent, high dielectric breakdown strengths, high resistivity and high energy-storage density, which was 27.74, 0.039, 245 MV/m, 1,625 MΩ m and 7.4 J/cm³, respectively. This implied that such kind of composites could be used as the dielectric layers of pulsed-power capacitors. In order to explain the relationships between the dielectric properties and the microcosmic physical and chemical properties, the samples were also studied by XRD, SEM and FTIR. The results demonstrated that the coupling agent could improve the filler-matrix interfaces and had significant influence on the dielectric properties of the nanocomposites.     

A study of structural, ferroelectric, ferromagnetic, dielectric properties of NiFe2O4–BaTiO3 multiferroic composites

The mixed spinel-perovskite multiferroic composites of xNiFe₂O₄-(1 ? x)BaTiO₃ (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) have been prepared by sol–gel method. The structure and morphology of the composites were examined by means of X-ray diffraction and transmission electron microscope. High-resolution transmission electron microscope image indicates a clear view of ferrite and ferroelectric phase. Moreover, we observed a fine interface between the two phases, where the coupling effect of ferrite and ferroelectric phase happened. The composites show excellent ferromagnetic and ferroelectric properties. The saturation magnetization (M_s) reaches to 24.139 emu/g for x = 0.6 at room temperature, the magnetization is about 2.37 emu/g for x = 0.6 when the temperature decreases to 90 k, and the polarization reaches to 3.75 μC/cm² for x = 0.1. Frequency dependent variations of dielectric constant and loss tangent for xNiFe₂O₄-(1 ? x)BaTiO₃ were studied in detail.     

Properties of calcium copper titanate and barium titanate filled epoxy composites for electronic applications: effect of filler loading and hybrid fillers

Inorganic ceramics such as calcium copper titanate, CaCu₃Ti₄O₁₂ (CCTO) and barium titanate (BaTiO₃) were used as fillers to produce epoxy thin film composites for capacitor application. The effects of filler types and loading range on the dielectric, tensile, morphology, and thermal properties of the epoxy thin film composites were determined. Results showed that epoxy thin film composites with 20 vol% filler loading of CCTO and BaTiO₃ showed good dielectric properties, thermal stability, and thermal conductivity. However, the tensile properties of the CCTO/epoxy thin film composite was reduced as the filler loading increased. On the other hand, the tensile properties of BaTiO₃/epoxy thin film composite improved as the filler loading increased. Hybrid fillers CCTO and BaTiO₃ filled epoxy composites were fabricated and the effect of hybrid fillers on the dielectric properties and morphology of the epoxy thin film composites were investigated. Results indicated that positive hybrid effect in dielectric constant and dielectric loss showed by the hybrid composites.     

Effects of SrO–B2O3–SiO2 glass additive on densification and energy storage properties of Ba0.4Sr0.6TiO3 ceramics

SrO–B₂O₃–SiO₂ glass powders were prepared and employed as sintering aids to reduce the sintering temperature of Ba_0.4Sr_0.6TiO₃ ceramics. The effects of glass content and sintering temperature on the densification, dielectric properties and energy storage properties of Ba_0.4Sr_0.6TiO₃ ceramics have been investigated. The relative density characterization results indicate that densification of Ba_0.4Sr_0.6TiO₃ ceramics with glass content becomes apparently from sintering temperature of 1,060 °C. XRD results show all Ba_0.4Sr_0.6TiO₃ ceramics exhibit a perovskite structure without the formation of a secondary phase. The dielectric constant and dielectric loss decreased gradually with increasing glass content. The relationship between dielectric constant and breakdown strength was discussed using the thermochemical model. A discharged energy density of 0.44 J/cm³ with an energy efficiency of 67.4% was achieved for Ba_0.4Sr_0.6TiO₃ ceramic with 2.0 wt% glass addition sintered at 1,180 °C.     

Effects of Kaolinite additions on sintering behavior and dielectric properties of CaCu3Ti4O12 ceramics

Commercial Kaolinite was employed as sintering aid to reduce the sintering temperature of CaCu₃Ti₄O₁₂ (CCTO) ceramics. The effects of Kaolinite content and sintering temperature on the densification, microstructure and dielectric properties of CCTO ceramics have been investigated. The density characterization results show that the addition of Kaolinite significantly enhanced the relative density of CCTO ceramics to about 92 %. X-ray diffraction results show CCTO ceramics with a low amount of Kaolinite exhibited perovskite-like structure, but 1.0 wt% Kaolinite additions resulted in the formation of a secondary phase, CaO–TiO₂–Al₂O₃–SiO₂ glass phase was formed and improved the dielectric constant of ceramics, which was supported by scanning electron microscopy–energy dispersive X-ray results. CCTO ceramic with 1.0 wt% Kaolinite addition possessed well temperature and frequency stability of dielectric constant. It was found that Kaolinite lowered the dielectric loss of the samples.     

机载龙伯透镜天线用聚苯乙烯泡沫塑料的制备及介电常数调控

针对雷达通讯微波频段新型轻质介电复合材料的迫切需求,开展高介电性能复合材料的研究具有现实意义。采用悬浮聚合法制备不同密度的聚苯乙烯泡沫,研究了聚苯乙烯泡沫的介电常数与密度之间的关系,分析了钛酸钡粉末的介电性能。采用干混法添加钛酸钡粉末制备介电常数可调控的轻质钛酸钡/聚苯乙烯复合泡沫。聚苯乙烯泡沫的介电常数随密度增大,表现出弱的频率依赖性和低介电损耗。钛酸钡粉末具有高的介电常数和较低的介电损耗。BaTiO_3/PS复合材料的介电常数随着BaTiO_3含量的增加而升高。相同介电常数的BaTiO_3/PS复合材料和聚苯乙烯泡沫相比,密度显著下降,说明添加BaTiO_3可以实现介电材料的轻质化。     

Comparison of theoretical predictions and experimental values of the dielectric constant of epoxy/BaTiO<Subscript>3</Subscript> composite embedded capacitor films

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/BaTiO₃ composite embedded capacitor films with various BaTiO₃ particles loading for 5 different sizes BaTiO₃ powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of BaTiO₃ powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/BaTiO₃ composites. And calculated dielectric constants of the BaTiO₃ powders were in the range of 100 to 600, which were lower than the dielectric constant of BaTiO₃ bulk ceramics probably due to the presence of voids or pores.     

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.     

Preparation and dielectric properties of BaTiO3-based X8R ceramics co-doped with BIT and CBS glass

The effects of Bi₄Ti₃O₁₂ (BIT) on phase purity and dielectric properties of BaTiO₃ (BT) ceramics have been investigated. Results show that BT samples doped with 1–3 mol% BIT adopt a single phase. However, secondary phase Bi₂Ti₂O₇ is observed when BIT content exceeds 3 mol%. Tetragonality and the Curie temperature (T _C) firstly increase and then decreases with an increase in BIT content. The 3 mol% BIT-doped BT ceramic sintered at 1,250 °C exhibits good dielectric properties of ε_r = 2,692, tan δ = 0.0152, ρ_v = 5.8 × 10¹² Ω cm, and the variation of dielectric constant as compared with that at room temperature is about ?20 % at ?55 °C and less than 11 % at 150 °C. It is found that the addition of calcium borosilicate glass (CBS) in BT-BIT ceramics can effectively lower the sintering temperature from 1,250 to 1,050 °C and further enhance the capacitance temperature stability. The permittivity decreases with an increase in CBS content from 1 to 10 wt%. Secondary phase BaBi₄Ti₄O₁₅ exists in the CBS doped BT-3BIT systems. All of CBS doped samples satisfy the X8R specification. Typically, the sample with 3 wt% CBS has ε_r = 1,789, tan δ = 0.0115, ρ_v = 9.67 × 10¹² Ω cm. The variation of permittivity as compared with that at room temperature is about ?12 % at ?55 °C and less than ± 11 % at 150 °C. The as-prepared materials have great potential as EIA X8R-type multilayer ceramic capacitors.     

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.     

Low-temperature sintering and microwave dielectric properties of Mg<Subscript>3</Subscript>B<Subscript>2</Subscript>O<Subscript>6</Subscript>-LMZBS composites

The Mg₃B₂O₆ ceramics with lithium magnesium zinc borosilicate (LMZBS) glass were prepared at a lower sintering temperature. The effects of the glass addition on the densification, phase development, microstructure and microwave dielectric properties of the Mg₃B₂O₆ ceramics were investigated. The addition of LMZBS glass improved the densification and lowered the sintering temperature of Mg₃B₂O₆ ceramics from 1,300 to 950 °C. X-ray diffraction patterns showed that Mg₃B₂O₆ transformed into Mg₂B₂O₅ and a new phase, Li₂ZnSiO₄, crystallized from the glass phase. Because of the high dielectric performance of these phases, Mg₃B₂O₆ mixed with 55 wt% LMZBS sintered at 950 °C for 3 h had ε_r = 6.8, Q × f = 50,000 GHz, and τ_f = ?64 ppm/°C at 7.28 GHz. The chemical compatibility of ceramic-glass composites with Ag was also investigated for LTCC.     

Dielectric,mechanical and thermal properties of polymer/BaTiO3 composites for embedded capacitor

Barium titanate (BaTiO₃) filled polymethylmethacrylate (PMMA) composites were prepared using the simple solution method followed by hot pressing. The content of BaTiO₃ was varied from 0 to 65 vol.%. Scanning electron microscopy showed good dispersion and adhesion of BaTiO₃ with the PMMA matrix. The dielectric constant of the composites increased significantly. There was weak dispersion in the dielectric constant of the composites (up to 45 vol.%) with frequency between 100 Hz and 15 MHz. The dissipation factor of the composites increased from 0.021 for pure PMMA to 0.029 for 45 vol.% composites. However, 65 vol.% composite showed dispersion in dielectric constant with increasing frequency and higher dissipation factor. The Lichtenecker equation agreed well with the experimental data. The microhardness and the glass transition temperature of the composites increased approximately 4.7-fold and 42 °C, respectively, compared to pure PMMA. The CTE of the 65 vol.% composite is close to that of copper.