Ultralow Dielectric Loss Research Articles

Insight into the Directional Thermal Transport of Hexagonal Boron Nitride Composites.

Ideal dielectric materials for microelectronic devices should have high directionally tailored thermoconductivity with low dielectric constant and loss. Hexagonal boron nitride (hBN) with excellent thermal and dielectric properties shows a promise for the fabrication of thermoconductive dielectric polymer composites. Herein, a simple method for the fabrication of lightweight polymer/hBN composites with high directionally tailored thermoconductivity and excellent dielectric properties is presented. The solid polymer/hBN composites are manufactured by melt-compounding and injection molding. The porous composites are successfully manufactured in an injection molding process through supercritical fluid (SCF) foaming. X-ray tomography provides direct visualization of the internal microstructure and hBN orientation, leading to an in-depth understanding of the directionally dependent thermoconductivity of the polymer/hBN composite. Shear-induced orientation of hBN platelets in the solid HDPE/hBN composites leads to a significant anisotropic thermal conductivity. The solid HDPE/23.2 vol % hBN composites show an in-plane thermoconductivity as high as 10.1 W m-1 K-1, whereas the through-plane thermoconductivity is limited to 0.28 W m-1 K-1. However, the generation of a porous structure via SCF foaming imparts in situ exfoliation, random orientation, and interconnectivity of hBN platelets within the polymer matrix. This results in highly isotropic thermoconductivity with higher bulk thermal conductivity in the lightweight porous composites as compared to their solid counterparts. Furthermore, the electrically insulating composites developed in this study exhibit low dielectric constant and ultralow dielectric loss. Thus, this study presents a simple fabrication method to develop lightweight dielectric materials with tailored thermal conductivity for modern electronics.

Enhanced dielectric breakdown strength in TiO2-SiO2-Al2O3 based ceramics prepared through hot-press assisted liquid phase sintering

Linear dielectric ceramics have received much attention due to high power density, fast discharge speed and ultralow dielectric loss, which are expected as promising candidates for the pulsed power system applications. However, their relatively low dielectric breakdown strength usually cannot meet the requirements of practical application. In this work, we adopt hot-press sintering method to enhance the dielectric breakdown strength of the TiO2-SiO2-Al2O3 based ceramics, and the dielectric breakdown strength reaches 77.5 kV/mm, which is 1.8 times as large as samples prepared by conventional sintering method. The effect of different sintering methods on microstructure, dielectric properties and dielectric breakdown strength is investigated. The improvement of dielectric breakdown strength can be ascribed to improved bulk density, smaller grain size, and reduced reduction of Ti4+ to Ti3+, associated with the applied external pressure and lower sintering temperature. Eventually, large power density (18.20 MW/cm3) is obtained in pulse overdamped discharge circuit. Meanwhile, the stored energy is also released in a short time (about 11.3 ns to release 90% of saturated energy density value).

High Insulation Resistivity and Ultralow Dielectric Loss in La-Doped SrTiO3 Colossal Permittivity Ceramics through Defect Chemistry Optimization

High performance LaxSr1–xTiO3 (0.000 ≤ x ≤ 0.018) ceramics were prepared by a traditional solid-state method and sintered in nitrogen atmosphere. The phase structure and micromorphology of the cera...

Colossal permittivity in BaTiO3-0.5wt%Na0.5Ba0.5TiO3 ceramics with high insulation resistivity induced by reducing atmosphere

The donor-acceptor co-doping grain-fine BaTiO3-0.5wt%Na0.5Ba0.5TiO3 (BT-0.5wt%NBT) ceramics are obtained by conventional solid-state reaction method and sintered in different atmospheres. The dielectric properties are sensitively influenced by the sintering atmosphere, which the colossal permittivity can be activated and increased by enhanced atmospheric reducibility with the increase of H2 content. However, the excessive H2 content can make a significant deterioration in dielectric loss and insulation resistivity. The impedance spectra, XPS and EPR measurements indicate that sintering atmosphere can effectively regulate the concentration and distribution of charge carriers (delocalized electrons, oxygen vacancies and defects), which induce the interfacial polarization and hopping polarization. When sintered in 0.1% H2/N2, the sample possesses a relatively good comprehensive performance with colossal permittivity (εγ>4×104), ultra-low dielectric loss (tanδ=0.0218) and high insulation resistivity (ρv>1011Ω·cm), which related to the moderate values of resistance and conduction activation energy for the grain boundaries.

Colossal permittivity and ultralow dielectric loss in (Nd0.5Ta0.5)xTi1-xO2 ceramics

Abstract Giant permittivity ceramic is one of the most significant classes of material to realize the miniaturization and integration of a high-performance capacitor. In this paper, to realize good giant dielectric properties, the (Nd0.5Ta0.5)xTi1-xO2 ceramics (NTTO x = 0.005, 0.01, 0.03, 0.05) were synthesized by a standard conventional solid-state reaction. Comparing with the previous co-doped TiO2 ceramics giant permittivity material system, NTTO ceramics perform extremely colossal permittivity and ultralow dielectric loss (1%NTTO: e = 82052, tanδ = 0.008 at 1 kHz; 5%NTTO: e = 170131, tanδ = 0.090 at 1 kHz). The broad distinction of the dielectric behavior between the (Nd0.5Ta0.5)xTi1-xO2 ceramics can be explained by the impedance analysis and the calculated polarization activation energies. The main electron-pinned defect-dipole (denoted as EPDD) polarization corresponds to the ultralow loss, embodying in the maximum value of Egb (the activation energy of the grain boundary), Ea2 (the EPDD polarization activation energies) and the minimum value of Ea1 (the total polarization activation energies). Though the interfacial polarization can cause the permittivity increase, it can also give rise to poor frequency stability and higher loss.

Influence of microstructure on magnetic and dielectric performance of Bi2O3-doped Mg Cd ferrites for high frequency antennas

Abstract The effects of microstructure on the magnetic and dielectric properties of Mg0.6Cd0.4Co0.05Fe1.95O4 spinel ferrites with the addition of 2.5 wt% Bi2O3 are investigated mainly for high frequency applications. The measurement results reveal that composites processed via low temperature co-fired ceramic (LTCC) technology at different sintering temperatures (900 °C, 920 °C, 930 °C, and 940 °C) possess excellent equivalent permeability (μ′) and permittivity (e′) (at 940 °C, μ′≈e′≈25), over a long frequency range from 1 to 100 MHz. The results also indicate that densification sintering results in ultra low dielectric loss tanδe and magnetic loss tanδμ (tanδe≈0.003, tanδμ≈0.035). In addition, the samples present enhanced magnetic properties, such as high saturation magnetization (approximately 37.94 emu/g) and appropriate coercivity (approximately 60.5 Oe) at 940 °C. This research presents the prospect of wide application of Mg Cd ferrites in high frequency applications.

A facile method for the preparation of furfurylamine based benzoxazine resin with high-frequency low dielectric constants and ultra-low dielectric losses

We report the furfurylamine/bisphenol-A based benzoxazine resin that can be used as the polymeric matrix of copper clad laminates for high-frequency applications. The investigation provides a facile and effective route to prepare the partial bio-based benzoxazine monomer in nonpolar solvent with high yield (92%) under the optimum condition. It should be noted that the incorporation of less aromatic furan rings not only increase the reactivity of benzoxazine, but also improve the cross-linking density of polybenzoxazines. Accordingly, the furfurylamine/bisphenol-A based benzoxazine film has the relatively high glass transition temperature (293 °C) and high char yield (50% at 800 °C). In particular, the furfurylamine/bisphenol-A based polybenzoxazine owning relatively low dielectric constants (2.60 ± 0.01, 5 GHz; 2.71 ± 0.01, 10 GHz) and ultra-low dielectric losses (0.007 ± 0.001, 5 GHz; 0.006 ± 0.001, 10 GHz), is suitable for applications in the field of high-frequency communications. Therefore, this work not only provides a simple path for the preparation of lignin based benzoxazine, but also gives some insight into the effects of furan rings on the cross-linking degree and high-frequency dielectric properties of polybenzoxazine.

Design and Preparation of Benzoxazine Resin with High-Frequency Low Dielectric Constants and Ultralow Dielectric Losses

The new main-chain benzoxazine copolymer oligomers with bulky hydrocarbon end groups are first designed and synthesized. In particular, the aliphatic diamine based copolymers owning low dielectric constants (<3) and ultralow dielectric losses (<0.005) under high frequencies, is suitable for applications in the field of high-frequency communications. Therefore, this work not only provides a facile and effective protocol to simultaneously obtain excellent high-frequency dielectric properties, and improved processing and thermal properties of benzoxazine resins, but also widens the scope of the design and synthesis of functional and high-performance thermosetting polymers.

The dimensional effect of MgTiO3 ceramic filler on the microwave dielectric properties of PTFE/MgTiO3 composite with ultra-low dielectric loss

PTFE matrix loaded with different volume fractions of MgTiO3 ceramic powder with particle sizes of around 5 μm and 15 μm (abbreviated as MT-5 and MT-15, respectively) was prepared. The microstructure, microwave dielectric properties and thermal properties of the composites were studied by scanning electron microscope, vector network analyzer and thermal dilatometer. The results show that PTFE/MT-15 composite exhibits higher relative density and better dielectric properties than the PTFE/MT-5 composite, since the former with coarse particles possesses lower surface energy to weaken the particle agglomeration effect. Even at 40% filler volume fraction, the ultra-low dielectric loss of PTFE/MT-15 composite can be maintained in the order of 10− 4 at 10 GHz. Different models are used to predict the dielectric constant of the composites. Among which, the effective medium theory shows the least deviation from the experimental results. PTFE matrix filled with 40V% MT-15 ceramic powder shows excellent microwave dielectric properties: er = 5.5, tanδ = 2.7 × 10− 4 (at 10 GHz), which may be a promising material in electronic packaging field.

Ultra-low dielectric loss BiSmMoO6 flexible tapes for hybrid integrated circuits

A low temperature co-fireable ceramic tape based on BiSmMoO6 (BSMO)-2 wt.% BBSZ (40Bi2O3:49B2O3:6SiO2:5ZnO) sinterable at 875 °C was successfully developed. The glass added ceramic was formulated into a well dispersed and homogenised slurry using xylene-ethanol binary mixture as solvent and fish oil as dispersant. The structural as well as microstructural properties of the casted tapes were analysed using XRD and SEM. The average surface roughness estimated using AFM was found to be 229 nm. The microwave dielectric properties of the green tapes, isostatically formed ones as well as sintered tapes were measured at 5 GHz and 10 GHz using split post dielectric resonator (SPDR) technique and found that resultant tape has ultra-low dielectric loss, of the order of 10−4. The BSMO-2 wt.% BBSZ tapes have shown a thermal expansivity of 12.3 ppm/˚C which is marginally higher than commercial tapes, but advantageous since closer to that of silver electrode.

Preparation of ultra‐low temperature sintering ceramics with ultralow dielectric loss in Na2O–WO3 binary system

AbstractA series of new microwave dielectric ceramics with ultralow dielectric loss in Na2O–WO3 binary system were prepared by the modified solid‐state reaction method at ultra‐low sintering temperatures. Three stable phases, namely Na2WO4, Na2W2O7 and Na2W4O13, were formed in the system. Their stability in the air, phase composition, compatibility with metal electrodes, microstructures, and microwave dielectric properties were investigated. In this binary system, the cubic structure Na2WO4 ceramic sintered at 565°C exhibited the best microwave dielectric properties with a permittivity of 5.6, a Q × f value of 124 200 GHz and a temperature coefficient of −63 ppm/°C at a frequency of 13.1 GHz. The Na2WO4 ceramic is chemically compatible with Ag and Al electrodes. Besides, the Na2WO4 ceramic has favorable stability in the air. Due to the excellent dielectric properties and favorable stability in the air, the Na2WO4 ceramic is a great candidate for LTCC devices.

A versatile foaming platform to fabricate polymer/carbon composites with high dielectric permittivity and ultra-low dielectric loss

A microcellular structure can effectively tune the dielectric properties of PVDF/carbon composite foams.

Multilayer-structured transparent MXene/PVDF film with excellent dielectric and energy storage performance

A novel multilayer-structured Ti3C2Tx MXene/poly(vinylidene fluoride) film with a high dielectric constant and ultralow dielectric loss is presented.

Origin of high dielectric permittivity and low dielectric loss of Sr0.985Ce0.01TiO3 ceramics under different sintering atmospheres

The effect of sintering atmosphere on the microstructure and dielectric properties of Sr0.985Ce0.01TiO3 were investigated in this article. The sample sintered in nitrogen achieves a colossal permittivity (∼12655) and ultralow dielectric loss (0.006) at room temperature and 1k Hz. XRD results reveal that all the samples belong to Pm3¯m space group and no secondary phase is detected. It can be verified by XPS measurement that the nitrogen sintered sample has the highest Ti3+ content. Five dielectric relaxations can be observed in the dielectric spectroscopy in the test temperature range from −130–500 °C, which can be attributed to the existence of Ti3+ ions, oxygen vacancies and the other associated defect clusters. Moreover, the off-center Ti3+ ions make a certain contribution to the high permittivity. The ultralow dielectric loss at room temperature could be ascribed to the formation of defect clusters in the samples sintered in air and nitrogen. These defect clusters which associated with the oxygen vacancy, such as Ti3+−VO..−Ti3+ and VSr"−VO¨ are able to localize charge carriers and restrain the motion and ionization of oxygen vacancies.

Temperature Stable Microwave Dielectric Ceramic CoTiNb2O8-Zn1.01Nb2O6 with Ultra-Low Dielectric Loss

(1 − x)CoTiNb2O8-xZn1.01Nb2O6 ceramics were prepared via a conventional solid-state reaction route to obtain near-zero τf. The effects of Zn1.01Nb2O6 content on the phase, microstructure and microwave dielectric properties of CoTiNb2O8 ceramics were investigated. X-ray diffraction (XRD) revealed a mixture of tetragonal rutile and orthorhombic columbite phases co-existed over the entire range. Both the sintering behavior and quality factor (Q × f) of matrix ceramics were enhanced effectively by the addition of Zn1.01Nb2O6. On the other hand, the relative permittivity (er) decreased linearly from 41.6 to 24.8. The temperature coefficient of resonant frequency (τf) could be controlled by adjusting the x value. When $$ x = 0.8 $$ , the composite ceramic sintered at 1200°C possessed optimum microwave dielectric properties with $$ \varepsilon_{r} \sim 27.8 $$ , $$ Q \times f \sim 94{,}700\;{\hbox{GHz}} $$ , and $$ \tau_{f} \sim 0 $$ ppm/°C.

Ultralow dielectric loss of Y and Mn alternately doped nonstoichiometric BST films

ABSTRACTA 1% Y and 1% Mn alternately doped nonstoichiometric (Ba0.6Sr0.4)0.8TiO3 (Y/Mn-BST) film was attempted to design and prepare by an improved sol-gel method on Pt/Ti/SiO2/Si substrates, and its ultralow dielectric loss with other dielectric properties was studied in this paper. Undoped, Y doped and Mn doped BST films were also compared. All films grow along (110) orientation and show polycrystalline cubic ABO3 perovskite structures. Pure film shows the weakest crystallization, while Y/Mn-BST film exhibits the strongest crystallization. Superfluous Ti acted as Ti doping makes B sites so saturated that superfluous Ti4+ ions have to enter A sites and first replace Sr2+ ions and then replace Ba2+ ions to show donor doping, thus result in the smallest lattice parameter and decreased Ba/Sr ratio. Doped Y3+ or Mn2+ ions only enter A sites and replace Ti4+ ions to reveal acceptor doping, and thuscause lattice parameters and Ba/Sr ratio a little larger than the undoped BST film. The Y/Mn-BST film shows the largest lattice parameter and increased Ba/Sr ratio with acceptor doping. Each nonstoichiometric BST film show smaller capacitance, tunability and dielectric loss than normal BST film, but the Y/Mn-BST film reveals better combination of dielectric properties in particular much smaller dielectric losses of 0.0051∼0.0067, thus show more obvious practicability and reliability in tunable microwave applications.

Correction to “Enhanced Dielectric Constant, Ultralow Dielectric Loss, and High-Strength Imide-Functionalized Graphene Oxide/Hyperbranched Polyimide Nanocomposites”

Correction to “Enhanced Dielectric Constant, Ultralow Dielectric Loss, and High-Strength Imide-Functionalized Graphene Oxide/Hyperbranched Polyimide Nanocomposites”

Crystal structure and wave-transparent properties of lithium aluminum silicate glass-ceramics

Lithium aluminum silicate (LAS) glass-ceramic exhibits high transmittance to electromagnetic wave and is an ideal radome material. LAS glass-ceramics with different ratios of Li/Al were prepared by sol-gel method. Crystallization behaviors and wave-transparent properties of sintered powders were characterized. β-spodumene was detected as the major phase that precipitated from the sample with 1:1 ratio between Li and Al, which exhibited ultra-low complex permittivity (epsilon, 2.78) and dielectric loss tangent values. The microwave transmittance in 2–18 GHz is higher than 90% when the thickness is within 1.7 mm, suggesting that this kind of LAS glass-ceramic possesses excellent wave-transparent properties.

SrFe12O19 based ceramics with ultra-low dielectric loss in the millimetre-wave band

Non-reciprocal devices such as isolators and circulators, based mainly on ferromagnetic materials, require extremely low dielectric loss in order for strict power-link budgets to be met for millimetre (mm)-wave and terahertz (THz) systems. The dielectric loss of commercial SrFe12O19 hexaferrite was significantly reduced to below 0.002 in the 75–170 GHz band by thermal annealing. While the overall concentration of Fe2+ and oxygen vacancy defects is relatively low in the solid, their concentration at the surface is significantly higher, allowing for a surface sensitive technique such as XPS to monitor the Fe3+/Fe2+ redox reaction. Oxidation of Fe2+ and a decrease in oxygen vacancies are found at the surface on annealing, which are reflected in the bulk sample by a small change in the unit cell volume. The significant decrease in the dielectric loss property can be attributed to the decreased concentration of charged defects such as Fe2+ and oxygen vacancies through the annealing process, which demonstrated that thermal annealing could be effective in improving the dielectric performance of ferromagnetic materials for various applications.

Ultralow Loss CaMgGeO4 Microwave Dielectric Ceramic and Its Chemical Compatibility with Silver Electrodes for Low-Temperature Cofired Ceramic Applications

ABSTRACT: A new ultralow dielectric loss cofired CaMg- GeO4 dielectric material with olivine structure was fabricated by the solid-state route. The X-ray patterns, Rietveld refinement, and microstructure revealed the characteristics of the synthesized material. CaMgGeO4 ceramic belongs to the orthorhombic system with a Pbmn space group. Sintered at 1300°C for 6h, the ceramic exhibited a densification of 96.5%, an ultrahigh quality factor (Q × f) of 124 900 GHz (tan δ = 1.24 × 10−4) at a frequency of 15.5 GHz, a permittivity (er) of 6.71, and a temperature coefficient of resonant frequency (τf) of −73.7 ppm/°C, and the average coefficient of thermal expansion of CaMgGeO4 was 12.4 ppm/°C. The sintering temperature of the CaMgGeO4 ceramic was reduced from 1300 to 940 °C with the addition of 5 wt % B2O3. The CaMgGeO4 + 5 wt % B2O3 ceramics exhibited favorable microwave dielectric performances: Q × f = 102,000 GHz (at 16.4 GHz), er = 5.80, and τf = −64.7 ppm/°C, respectively. In addition, the CaMgGeO4 ceramic did not react with Ag electrodes, which could be advantageous in low-temperature cofired ceramic multilayer microwave devices. KEYWORDS: Microwave dielectric properties, CaMgGeO4, LTCC, ultralow dielectric loss