Microwave Dielectric Ceramics Research Articles

Temperature-stable and ultralow-loss (1 − x)CaSmAlO4–xSr2TiO4 microwave dielectric solid-solution ceramics

The (1 − x)CaSmAlO4–xSr2TiO4 (0.01 ≤ x ≤ 0.06) microwave dielectric ceramics were for the first time prepared by a conventional solid-state method. The phase composition, sintering behavior, microstructure and microwave dielectric properties were investigated as function of sintering temperature and composition. A single-phase solid solution with K2NiF4-type tetragonal structure was formed in the range of 0.02 ≤ x ≤ 0.06. All samples are well densified with very little pores. The addition Sr2TiO4 greatly improves dielectric properties originally by restraining the secondary phase and then deteriorates Q × f value because of decreasing tolerance factor. Moreover, the τf value dominated by the thermal expansion coefficient increases lineally as x rises. Finally, excellent microwave dielectric properties of er ~ 18.1, Q × f ~ 140,433 GHz (8.5 GHz), and a near-zero τf ~ + 0.05 ppm/°C can be obtained in the x = 0.05 ceramic sintered at 1425 °C.

Microwave dielectric property adjustment of CoZrNb2O8 ceramics by CaTiO3 addition

Temperature stable microwave dielectric ceramics CoZrNb2O8-xCaTiO3 (x = 1/60 ~ 1/10) were fabricated by a solid-state technique. The phase formation and sintering behavior were detected for the purpose of structure–property relationship exploration. Appropriate rate of CaTiO3 addition was benefit to the sintering temperature decrease of CoZrNb2O8. From x = 1/50 to x = 1/10, unexpected CaNb2O6 and Ti2Nb10O29 phases both formed, consequent on the chemical reaction between CoZrNb2O8 and CaTiO3. Co-based oxide might separate out in the form of liquid phase and decrease the sintering temperature. Increasing CaTiO3 ration degraded the quality factor Q × f, but at the same time enhanced the dielectric constant er and temperature coefficient of resonant frequency τf. According to the Lichtenecker mixing rule, the estimated microwave dielectric properties basically agreed well with the measured values at first. However, excessive CaTiO3 incorporation caused lattice defects and gave noticeable deviation. In current work, CoZrNb2O8-1/40CaTiO3 composite displayed a rather small τf with Q × f= 64,600 GHz at 1225 °C.

Novel low-εr MGa2O4 (M = Ca, Sr) microwave dielectric ceramics for 5 G antenna applications at the Sub-6 GHz band

Two novel low-εr gallates MGa2O4 (M = Ca, Sr) have been synthesized via a standard solid-state reaction method. According to the X-ray diffraction results, CaGa2O4 crystallizes in space group Pna21 with an orthorhombic symmetry, while SrGa2O4 belongs to the monoclinic P21/c system. Both ceramics show ever-improving microstructures with the increasing sintering temperature. The optimal microwave dielectric properties (εr = 9.2, Qf = 66,000 GHz, τf =–85 ppm/°C for SrGa2O4 and εr = 10.6, Qf = 15,400 GHz, τf =–58 ppm/°C for CaGa2O4) are obtained when sintered at 1275 °C. A patch antenna is fabricated using SrGa2O4 ceramics as the substrate, which realizes a return loss of –19.94 dB and total efficiency of –1.38 dB (72.8 % in power ratio) at 4.84 GHz. The exceptional performances indicate that SrGa2O4 ceramics are promising candidates for antenna applications at the Sub-6 GHz band.

Novel temperature stable Li2Mg3ZrO6 microwave dielectric ceramics with Ca0.8Sr0.2TiO3 addition

Novel temperature stable Li2Mg3ZrO6 microwave dielectric ceramics were fabricated by a conventional solid-state route. With increasing Ca0.8Sr0.2TiO3 content x, CaZrO3 phase was formed and a near-zero τf value was obtained at 1350 °C for x = 0.21. Li2Mg3ZrO6-based ceramics displayed well microwave dielectric properties of εr = 16.2, Q × f = 46370 GHz, τf = 4.5 ppm/°C when Ca0.8Sr0.2TiO3 content x is 0.21.

Ultra-high Q Ba(Mg1/3Ta0.675)O3 microwave dielectric ceramics realized by slowly cooling step process and the simulation design for hairpin dielectric filters

With the development of 5G technology, it would inevitably lead to the problem of energy consumption owing to the massive construction of 5G base stations and the increase in the number of antenna channels. Dielectric filters as the core component in the base station, the energy consumption was closely related to its insertion loss, which could be achieved by reducing the dielectric loss (tanδ = 1/Q) of microwave dielectric ceramics. In this work, in order to further enhance the Q × f value, the slowly cooling step process was innovatively introduced to the Ba(Mg1/3Ta0.675)O3 ceramic. The optimal microwave dielectric properties were obtained in Ba(Mg1/3Ta0.675)O3 ceramic with the step temperature of 1500 °C: εr = 24.767, Q × f = 298,051 GHz, τf = −0.66 ppm/°C. Based on ultra-high Q Ba(Mg1/3Ta0.675)O3 ceramic, the hairpin dielectric filter with high integration and low insertion loss was designed and simulated. Compared with traditional RT/duroid5870 dielectric substrate, the circuit area was reduced by more than 6 times and the passband insertion loss (|S21| < 1 dB) was decreased by more than 50%. The current work could provide a solution for the low-power applications of microwave dielectric devices in 5G base stations.

Microwave Dielectric Ceramic Materials and Their Industry Development Overview and Future Prospects

Nowadays, microwave dielectric ceramics are widely used in all kinds of modern communication equipment, becoming the key material for manufacturing microwave dielectric filters and resonators. With the rapid development of related fields, the scope of application of microwave dielectric ceramics has been further expanded. On this basis, this paper explores the development history of microwave dielectric ceramics and the situation and future outlook of its industry. By combining historical events and data, the development history of microwave dielectric ceramics is described. The situation is also analysed and discussed in the context of the times and current events to provide an objective evaluation and forecast of the industry. The final results show that in the context of the new era of 5G, the microwave dielectric ceramics industry has entered a brand new stage of development and it presents a huge potential for innovation and development.

Improved Zn0.9Mg0.1Al2O4 Microwave Dielectric Ceramics with High Thermal Conductivity

Improved Zn0.9Mg0.1Al2O4 Microwave Dielectric Ceramics with High Thermal Conductivity

Optical, morphological, electrical properties of ZnO-TiO2-SnO2/CeO2 semiconducting ternary nanocomposite

Low dielectric constant and low dielectric loss with moderate wide bandgap, novel semiconducting metal oxide composites are useful materials for applying optoelectronic, microwave dielectric ceramics. A less dielectric constant is required for wireless communication to reduce the cross pairing between conductors and also for fast signal transmission. In the present study, the structural, optical, and dielectric properties of ternary ZnO - TiO2 added with SnO2/CeO2 semiconducting nanocomposite materials were investigated and synthesized by the solid-state gelation method. The samples were sintered at a temperature of 450 0C. The X-ray diffraction patterns of composites revealed the existence of TiO2 anatase phase, SnO2, and CeO2. The average crystallite size at d101 was measured using the Scherer method, ranging from 6.18 nm to 9.13 nm. The overall crystallite size was calculated using the Size-strain plot method, and it is in the range of 14.8 nm to 17.16 nm. The surface morphology of all samples appears uniform in size and spherical shape. The average particle size of grains was 35 nm. The absorbance properties studied by UV–Visible spectroscopy and bandwidth were 2.6 eV calculated using Tauc’s plot method, and it reveals the formation of new energy levels. The dielectric properties of pellet dimensions of 1 mm thickness and 10 mm diameter, measured from the LCR meter, are indicated at 1 kHz frequency. The most significant dielectric constant (εr) and lowest loss tangent (Tan δ) are 53.89 and 0.25 for pure ZnO - TiO2, and the lowest dielectric constant (εr) and less loss tangent (Tan δ) are 9.69 and 0.38 for 1 wt% CeO2 doped to ZnO - TiO2. The conductivity of the composite is in the range of 10-7 S/cm. With additive concentration to ZnO - TiO2, both SnO2 and CeO2 are equally potential and modifies the parameters due to the similar bandgaps and more oxygen availability.

Machine learning approaches for permittivity prediction and rational design of microwave dielectric ceramics

Low permittivity microwave dielectric ceramics (MWDCs) are attracting great interest because of their promising applications in the new era of 5G and IoT. Although theoretical rules and computational methods are of practical use for permittivity prediction, unsatisfactory predictability and universality impede rational design of new high-performance materials. In this work, based on a dataset of 254 single-phase microwave dielectric ceramics (MWDCs), machine learning (ML) methods established a high accuracy model for permittivity prediction and gave insights of quantitative chemistry/structure-property relationships. We employed five commonly-used algorithms, and introduced 32 intrinsic chemical, structural and thermodynamic features which have correlations with permittivity for modeling. Machine learning results help identify the permittivity decisive factors, including polarizability per unit volume, average bond length, and average cell volume per atom. The feature-property relationships were discussed. The optimal model constructed by support vector regression with radial basis function kernel was validated its superior predictability and generalization by verification dataset. Low permittivity material systems were screened from a dataset of ∼3300 materials without reported microwave permittivity by high-throughput prediction using optimal model. Several predicted low permittivity ceramics were synthesized, and the experimental results agree well with ML prediction, which confirmed the reliability of the prediction model.

Impedance spectroscopy, B-site cation ordering and structure–property relations of (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics for 5G dielectric waveguide filters

Dense (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics were synthesized via solid-state reaction. The crystal structure and microwave dielectric properties of the ceramics were systematically investigated. Rietveld refinement revealed that when x ≤ 0.2, the ceramics had a rhombohedral structure with an R-3c space group. When x ≥ 0.5, the ceramics had an orthorhombic structure with a Pbnm space group. Selected area electron diffraction and Raman spectroscopy analyses proved that the microwave dielectric ceramics had a B-site order, which accounted for the great improvement in microwave dielectric properties. The content of oxygen vacancies was identified through X-ray photoelectron spectroscopy, and the change rule of Q × f was closely related to oxygen vacancy content. The perturbation of A-site cations had an important influence on dielectric constant. Specifically, with the increase in Ti4+ content, the perturbation effect of the A-site cations was enhanced and dielectric constant increased. When x = 0.65, the temperature coefficient of resonant frequency of the (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 microwave dielectric ceramics was near zero. The optimal microwave dielectric properties of 0.35LaAl0.9(Mg0.5Ti0.5)0.1O3–0.65CaTiO3 were εr= 44.6, Q × f = 32,057 GHz, and τf= +2 ppm/°C.

Zn-modified Li3Mg2SbO6 microwave dielectric ceramics with high-quality factor

Well-densified Li3(Mg1−xZnx)2SbO6 (0.00 ≤ x ≤ 0.08) microwave dielectric ceramics were synthesized via a two-stage sintering process. The effects of Zn2+ substitution on the microstructure and microwave dielectric properties were investigated. All samples were identified as pure phase via the XRD detection. Remarkable microwave dielectric properties with a near-zero τf value were obtained in the Li3(Mg1−xZnx)2SbO6 (x = 0.04) sample sintered at 1325 °C for 5 h: εr = 7.8, Q × f = 97,719 GHz (13.4 GHz), τf = − 6 ppm/°C. The high Q × f value was related with the FWHM and grain size effect. All experimental results indicate that the Li3(Mg1−xZnx)2SbO6 ceramics are promising for 5G communication applications.

Ultralow-loss (1-x)CaWO4-xNa2WO4 (x = 0.1, 0.2) microwave dielectric ceramic for LTCC applications

In this work, the (1-x)CaWO4-xNa2WO4 (x = 0.1, 0.2, denoted as 0.9CW-0.1NW and 0.8CW-0.2NW, respectively) ultralow-loss microwave dielectric ceramics were prepared via solid-state reaction method. Using low melting-point Na2WO4 as sintering aid to prepare CaWO4Na2WO4 composite ceramics, the sintering temperature of CaWO4 was successfully reduced while maintaining excellent microwave performance. The optimal microwave dielectric properties have been achieved at 900 °C for 0.9CW-0.1NW ceramic: εr = 9.0, Q × f = 105660 GHz, tanδ = 1.1 × 10−4 and τf = −35.4 ppm/°C at a frequency of 12.0 GHz. For the 0.8CW-0.2NW ceramic, the optimal microwave dielectric properties have been obtained at 740 °C, with εr = 8.5, Q × f = 97014 GHz, tanδ = 1.2 × 10−4 and τf = −37.4 ppm/°C at a frequency of 11.8 GHz. In summary, both composite ceramics exhibit low sintering temperatures, excellent dielectric properties and chemical compatibility with the Ag electrode. The findings of this study provide an effective approach to prepare novel composite ceramics as promising candidates for LTCC applications.

Preparation, phase assemblage and microwave dielectric properties of AlPO4-BPO4-SiO2 ternaries

Microwave dielectric ceramics with low dielectric permittivities (Ɛr<6), high quality values and temperature sable resonator frequencies are strongly desired with the development of millimeter wave communication. In this paper, a compositional design for low-k materials was proposed from the point view of crystal chemistry. AlPO4-BPO4-SiO2 glass-ceramics were prepared by traditional solid state and sol-gel processes, respectively. The sintering behaviors, phase assemblages, microstructures and microwave dielectric properties of AlPO4-BPO4-SiO2 ternaries have been studied. The solid solubility, glass forming ability and crystallization of the AlPO4–BPO4–SiO2 ternaries can be understood by considering the structural flexibility via the degree of ionicity i of the bonds in the ternaries. All compositions demonstrate low dielectric permittivity less than five and negative temperature coefficient of resonant frequency. Maximum Q × f value could be obtained for the 0.45AlPO4–0.45BPO4–0.10SiO2 composition prepared by sol-gel process after sintering at 1175 °C/2 h: Ɛr∼4.16, Q × f∼59,519.

Structure and chemical bond characteristics of two low-εr microwave dielectric ceramics LiBO2 (B = Ga, In) with opposite τf

Two novel microwave dielectric materials LiBO2 (B = Ga, In) were synthesized by a solid-state reaction method. The orthorhombic structured LiGaO2 sintered at 1075 °C for 4 h exhibits a relative density of 96.1 ± 0.2 % and dielectric properties, namely, εr ∼ 5.82 ± 0.01 (16.7 ± 0.1 GHz), Q × f = 24,500 ± 2000 GHz, and τf ∼ -74.3 ± 2 ppm/°C. Meanwhile, the tetragonal structured LiInO2 sintered at 920 °C for 4 h exhibits a relative density of 85.3 ± 0.2 % and dielectric properties, namely, εr ∼ 9.6 ± 0.01 (15.2 ± 0.1 GHz), Q × f = 39,600 ± 2000 GHz, and τf ∼ 9.8 ± 2 ppm/°C. The dielectric properties were investigated by chemical bond theory, and results indicate that the τf value is closely related to the bond ionicity. The good chemical compatibility of LiInO2 ceramics with silver electrodes makes it a potential material for LTCC technology.

Ultra-high quality factor of Mg6Ti5O16-based microwave dielectric ceramics with temperature stability

Mg6Ti5O16-based ceramics with ultra-high quality factor and temperature stability were prepared by a conventional solid-state reaction route. The effects of Ca2+ on phase composition, microstructure, and microwave dielectric properties of Mg6Ti5O16 ceramics were systematically investigated. X-ray diffraction (XRD) patterns and energy dispersive spectroscopy (EDS) analysis confirmed that the ceramics were composed of MgTiO3, MgTi2O4, and CaTiO3 with all Ca2+ contents. A kind of microwave dielectric ceramics based on Mg6Ti5O16 was developed, and the microwave properties of Mg6Ti5O16 ceramics can be effectively improved by doping of Ca2+. After sintering at 1360 °C for 4 h, Mg6Ti5O16 ceramics doped with x = 0.35 Ca2+ exhibited an ultra-high quality factor of 100432 GHz (at 9 GHz) and a dielectric constant of 19.87. The resonant frequency temperature coefficient was − 3.0 ppm/°C during the temperature range of 25–85 °C. It is a promising material in the field of microwave communication.

Preparation and microwave properties of ZnTiNb2O8/SmTiNbO6composite dielectric ceramics

In order to get a microwave dielectric ceramics having near zeroτƒ, different ratio of ZnTiNb2O8and SmTiNbO6powders are sintered together at different temperature. XRD and SEM of these composite ceramics are tested to analyze the composition. The microwave properties and density of the composite ceramics are measured in order to find the best ratio of ZnTiNb2O8and SmTiNbO6. For (1-x)ZnTiNb2O8-xSmTiNbO6ceramics, the ceramics have very good microwave properties(εr= 24.63, Q*ƒ=11846GHz,τƒ= 0.16ppm/℃) when x is 0.35.

A Critical Review on the Fabrication Processes and Applications of Microwave Dielectric Ceramics Ba6-3xNd8,2xTi18O54

A Critical Review on the Fabrication Processes and Applications of Microwave Dielectric Ceramics Ba6-3xNd8,2xTi18O54

Synthesis of CaAl2xB2O4+3x: Novel microwave dielectric ceramics with low permittivity and low loss

Novel CaAl2xB2O4+3x (x = 0.25, 0.5, 0.75, and 1) ceramics were prepared via solid-state reaction method. The investigation is concentrated on sintering behavior, phase composition and dielectric properties of CaAl2xB2O4+3x ceramics with various ratios of Al2O3 content. The optimal sintering temperature and the content of CaAl2B2O7 are highly related to the variation of x value. CaAl2xB2O4+3x ceramics possess excellent microwave dielectric properties: εr = 5.8 ± 0.05, Q × f = 63,338 ± 2690 GHz (@13.57 GHz), and τf=-29 ± 2 ppm/℃ when sintered at 940 ℃ for x = 0.5. Comparing the properties of CaAl2xB2O4+3x ceramics with reported borate ceramics, the ceramics prepared in this study with low dielectric loss and low sintering temperature have promising prospects in LTCC technology.

Design of a High-Efficiency and -Gain Antenna Using Novel Low-Loss, Temperature-Stable Li2Ti1-x(Cu1/3Nb2/3)xO3 Microwave Dielectric Ceramics.

Microwave dielectric ceramics are vital for filters, dielectric resonators, and dielectric antennas in the 5G era. It was found that the (Cu1/3Nb2/3)4+ substitution can effectively adjust the TCF (temperature coefficient of resonant frequency) of Li2TiO3 and simultaneously increase its Q × f (Q and f denote the quality factor and the resonant frequency, respectively) value. Notably, excellent microwave dielectric properties (εr (permittivity) ≈ 18.3, Q × f ≈ 77,840 GHz, and TCF ≈ +9.8 ppm/°C) were achieved in the Li2Ti0.8(Cu1/3Nb2/3)0.2O3 (LTCN0.2) ceramic sintered at 1140 °C. Additionally, the sintering temperature of LTCN0.2 was reduced to 860 °C by the addition of 3 wt % H3BO3, exhibiting superior microwave dielectric properties (εr ≈ 21.0, Q × f ≈ 51,940 GHz, and TCF ≈ 1.4 ppm/°C) and being chemically compatible with silver. Moreover, LTCN0.2 + 3 wt % H3BO3 ceramics were designed as a patch antenna and a dielectric resonator antenna, both of which showed high simulated radiation efficiencies (88.4 and 93%) and gains (4.1 and 4.03 dBi) at the center frequencies (2.49 and 10.19 GHz). The LTCN0.2 + 3 wt % H3BO3 materials have promising future application for either 5G mobile communication devices and/or in low-temperature co-fired ceramic technology owing to their high Q, low sintering temperature, small density, and good temperature stability.

The Dielectric Constant of Ba6-3x(Sm1-yNdy)8+2xTi18O54 (x = 2/3) Ceramics for Microwave Communication by Linear Regression Analysis.

The electronics related to the fifth generation mobile communication technology (5G) are projected to possess significant market potential. High dielectric constant microwave ceramics used as filters and resonators in 5G have thus attracted great attention. The Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramic system has aroused people’s interest due to its underlying excellent microwave dielectric properties. In this paper, the relationships between the dielectric constant, Nd-doped content, sintering temperature and the density of Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramics were studied. The linear regression equation was established by statistical product and service solution (SPSS) data analysis software, and the factors affecting the dielectric constant have been analyzed by using the enter and stepwise methods, respectively. It is found that the model established by the stepwise method is practically significant with Y = −71.168 + 6.946x1 + 25.799x3, where Y, x1 and x3 represent the dielectric constant, Nd content and the density, respectively. According to this model, the influence of density on the dielectric constant is greater than that of Nd doping concentration. We bring the linear regression analysis method into the research field of microwave dielectric ceramics, hoping to provide an instructive for the optimization of ceramic technology.