Microwave Dielectric Ceramic Materials Research Articles

Recent progress in dielectric resonator antenna: Materials, designs, fabrications, and their performance

Dielectric resonator antenna (DRA) has secured an esteemed position in the field of antenna engineering technology due to its versatile features, including compactness, light-weight, low loss, high radiation efficiency, ease of excitation, diverse feeding techniques, multiple excitation modes, ease of integration with passive and active microwave integrated circuit components, a wide variety of available materials, simple fabrication techniques, and high degree of flexibility over wide frequency range. This article presents a comprehensive up-to-date review of research carried out in the field of DRA technology which includes an overview of DRA technology, its history, present status, and prospects. The basic parameters of microwave dielectric ceramic materials and the classification of materials based on utilization and material parameters are briefly discussed. The applications of DRA in different fields of science, engineering, and technology, overview of different reported DRA shapes, and the feeding techniques used to excite different modes of DRA are mentioned. Based on the control of DRA permittivity, shape/geometry, feeding techniques, and structural modifications, performance parameters engineering of DRA and its achievable performance in terms of low profile, compactness, high gain, wide beam, circular polarization, wide bandwidth, DRA decoupling methods for multiple input multiple output arrays, dielectric patch antenna, filtering DRA, and reconfigurable DRA are discussed. Different techniques used to attain and enhance the particular performance of DRA are highlighted. This review article also dilates upon the fabrication processes and characterization methods of DRA microwave dielectric ceramics, which play a very vital role in controlling the performance and properties of DRA.

High quality of LiMg0.9Zn0.06Ni0.04PO4-TiO2 microwave ceramic and its application for 5G dielectric waveguide bandpass filter

A new microwave dielectric composite ceramic (1-x) wt%LiMg0.9Zn0.06Ni0.04PO4-x wt%TiO2 (0 ≤ x ≤ 18 wt%) was synthesized in the low sintering temperature range of 850 °C − 975 °C by the solid-state reaction method. The XRD diffractogram confirmed the coexistence of LiMg0.9Zn0.06Ni0.04PO4 and TiO2, and no second phase was detected. Due to their opposite τf values, the τf values of LiMg0.9Zn0.06Ni0.04PO4 solid solution ceramics were adjusted by adding different volume fractions of TiO2. The composite ceramic with x = 15 wt% sintered at 975 °C shows desirable microwave dielectric properties of εr∼10.30, Q×f ∼ 58,400 GHz (tan δ = 2.093 ×10−4), and τf ∼ + 4.04 ppm/ °C (at ∼12 GHz). Based on the 85 wt% LiMg0.9Zn0.06Ni0.04PO4-15 wt% TiO2 ceramics, a fourth order dielectric waveguide filter filled with composite ceramics is designed and packaged for the RF front-end of the China Mobile 5 G base station. The test results show that the center frequency of the filter is 4.65 GHz, the working bandwidth is 300 MHz, the filter has a good out of band rejection capability, and the insertion loss in band is 0.18 dB. Combined with the filter test data and material performance, the designed dielectric waveguide filter meets the communication requirements of the base station, and the higher Q×f microwave dielectric ceramic material can achieve low insertion loss and excellent frequency selection performance of the filter.

Characterization of structural and electrical properties of Ca0.61Nd0.26TiO3 ceramic tailored by complex ions (Al0.5Nb0.5)4+

Miniaturization and low power dissipation are a trend for the development of ceramic-based microwave devices. Therefore, the decrease of the dielectric loss properties of microwave dielectric ceramic material compounds with a high dielectric constant is considered a quite important subject. In this work, the Ca0.61Nd0.26TiO3 material configuration with orthorhombic perovskite structure was thoroughly investigated by applying the strategy of (Al0.5Nb0.5)4+ substitution at the B-site. More specifically, the Ca0.61Nd0.26Ti1-x(Al0.5Nb0.5)xO3 sample with a nearly 60% increase in the quality factor (Q×f) was obtained. Also, the relationship between the structural and the electrical properties of Ca0.61Nd0.26Ti1-x(Al0.5Nb0.5)xO3 (0 ≤ x ≤ 0.15) samples were explored via performing X‐ray diffraction (XRD) measurements, Raman spectra, transmission electron microscopy (TEM) and calculation of the insulation resistance, etc. The extracted outcomes divulged that samples at x = 0–0.12 formed a single perovskite-structured phase, while the grain size of samples decreased by increasing the x value, leading to a drop decline of both the dielectric constant (εr) and electrical conductivity. Additionally, insights from the acquired Raman spectra confirmed that the stressed-rigid oxygen octahedral networks could lower the positive τf value of Ca0.61Nd0.26TiO3-based ceramic compounds. Interestingly, as the doping content of (Al0.5Nb0.5)4+ increased, the Ti3+ in samples was restrained at x = 0.04, whereas the insulation properties of the samples increased. Hence, the conductivity loss was declined. Furthermore, the TEM images illustrated the appearance of a 1: 1 ordered structure at the B-site of the (Al0.5Nb0.5)4+-doped samples. As a result, the Q×f value of the samples raised from 11,095GHz at x = 0–17,802 GHz at x = 0.12, enhanced by 60%. On top of that, for the sample with x = 0.15, the existence of the Ca2Nb2O7 phase deteriorated the microwave dielectric properties of the Ca0.61Nd0.26Ti1-x(Al0.5Nb0.5)xO3 samples, and especially Q×f value.

Microwave and terahertz properties of porous Ba4(Sm,Nd,Bi)28/3Ti18O54 ceramics obtained by sacrificial template method

AbstractMicrowave and terahertz communications are increasingly significant, however, the lack of material information in terahertz band limits their development. Moreover, few lightweight materials with a high relative dielectric constant () are found suited for satellite communication and wearable devices. In this study, we developed lightweight porous Ba4[(Sm0.1Nd0.9)0.9Bi0.1]28/3Ti18O54 (BSNBT) ceramics exhibiting a total porosity ranging from 6.3% to 26.5% (bulk density ranging from 5.47 to 4.29 g/cm3) and relatively high ranging from 85.6 to 56.8, which were obtained by sacrificial template method using polymethyl methacrylate spheres (PMMAs) of varying average particle sizes, from 9 to 34 μm, as sacrificial materials. A high refractive index ranging between 7.5 and 8.9 and a low absorption coefficient of approximately 17 cm−1 at 0.3 THz were obtained for the porous ceramics with different total porosities derived from PMMAs with average particle sizes of 9 and 19 μm. Furthermore, effective medium and Mie scattering theories were applied to understand the effects of porous structure on the dielectric properties in microwave and terahertz frequency ranges, respectively, owing to the different wavelengths in the BSNBT matrix. The results of this study suggest that introducing a porous structure can effectively exploit lightweight microwave dielectric ceramic materials and provide valuable information on their terahertz response mechanism.

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.

A new high-Q×f Li4NbO4F microwave dielectric ceramic for LTCC applications

A novel microwave dielectric ceramic material, Li4NbO4F, was fabricated by the solid-state reaction method. The microwave dielectric properties, sintering characteristics, and crystal structures of the Li4NbO4F ceramic samples were investigated. It was found that the Li4NbO4F ceramic samples can be successfully sintered at low temperatures (e.g., 750–875 °C). The samples exhibited a single cubic rock salt phase and possessed homogenous microstructures and outstanding microwave dielectric properties. The optimal properties of Q × f = 61111 GHz, εr = 15.2, and τƒ = −51 ppm/°C were achieved in the ceramic sample sintered at 825 °C. Additionally, the ceramic samples showed superior compatibility with Ag, indicating that Li4NbO4F is a promising low-temperature co-fired ceramic (LTCC) material.

The sintering behavior and microwave dielectric properties of 0.67CaTiO3–0.33LaAlO3 ceramics sintered at medium temperatures with the additives of H3BO3–Li2CO3

0.67CaTiO3–0.33LaAlO3 (CTLA) microwave dielectric ceramic materials with the additives of H3BO3, Li2CO3 or H3BO3–Li2CO3 were prepared by a conventional solid-state reaction method. The effects of the sintering additives on the densification behavior, phase compositions, microstructures, and microwave dielectric properties of the CTLA ceramic samples were investigated. It was found that the binary additive of H3BO3–Li2CO3 effectively promoted the densification and lowered the sintering temperature of the CTLA ceramic samples without a significant decrease in their Q × f values. For example, with an addition of 0.2 wt% H3BO3–0.1 wt% Li2CO3, the optimal microwave dielectric properties of er = 45.5, Q × f = 31,771 GHz and a near-zero τf of 2.43 ppm/℃ were obtained in the CTLA ceramic sample sintered at only 1175 ℃, which is significantly lower (~ 225 ℃) compared to the sintering temperatures of conventionally sintered CTLA ceramics.

Microwave dielectric property modification of Ba4Nd9.33Ti18O54 ceramics by the substitution of (Al0.5Nb0.5)4+ for Ti4+ and the addition of NdAlO3

In this work, Ba4Nd9.33Ti18O54 (BNT) microwave dielectric ceramic materials fabricated by a conventional solid-state reaction method was compositionally modified via the replacement of Ti4+ by (Al0.5Nb0.5)4+ and the addition of NdAlO3 to enhance the temperature stability (τf) and quality factor (Q×f) of the BNT ceramic materials. In the ceramic samples of Ba4Nd9.33(Al0.5Nb0.5)xTi18-xO54 (BNANT), an increase in the concentration of (Al0.5Nb0.5)4+ (i.e., x from 0 to 1.6) effectively improved both the τf (from 67.5 to 12.6 ppm/°C) and the Q×f (from 9260 to 10245 GHz) despite the fact that the excessively high concentration of (Al0.5Nb0.5)4+ (i.e., x = 1.6) severely deteriorated the Q×f, and the τf was still not at a near-zero level. Therefore, NdAlO3 was introduced into the BNANT ceramic materials as a τf compensator. In the binary system of (1-y)Ba4Nd9.33(Al0.5Nb0.5)1.2Ti16.8O54-yNdAlO3, a near-zero τf level of −2.06 ppm/°C with Q×f = 13680 GHz and dielectric constant (εr) = 70 was achieved at y = 0.55.

Determining the Quality Factor of Dielectric Ceramic Mixtures with Dielectric Constants in the Microwave Frequency\xa0Range

Microwave dielectric ceramic materials are extensively utilized in microwave applications because of their high dielectric constants and quality factors. These applications also require ceramics of zero temperature coefficients at the resonant frequency (τf), which can be realized through mixing a ceramic that one is interested in with another ceramic with −τf, or by performing the ionic substitution. With the mixing/ionic substitution, it is indispensable to compute the quality factors precisely. Previous study indicates that the quality factor depends on the grain size, porosity, internal strain, structure, phase evolution, and conductivity etc. Here we derive a quality factor formula based on the definition, which works very well for multiphase composites, single phase solid solutions, and equivalent ionic substituted single phase materials. Our formula calculation and fits to the previous experimental results demonstrate that the quality factor of the ceramic mixtures strongly depend on the dielectric constants and the dielectric constant variation index. Our results suggest that the impacts from grain size, porosity, and internal strain etc. can be summarized to the dielectric constant or dielectric constant variation index, which is of great importance for future design of high performance microwave dielectric ceramics.

Pseudo Phase Diagram and Microwave Dielectric Properties of Li2O–MgO–TiO2 Ternary System

Li2O–MgO–TiO2 ternary system is an important microwave dielectric ceramic material with excellent properties and prospect in both scientific research and application. A phase diagram of the Li2O–MgO–TiO2 ternary system was established in this article, based on earlier research results and our present work. Microwave dielectric properties with compositions in different regions of the phase diagram have been analyzed. We found that the 0.33 Li2MgTi3O8–0.67 Li2TiO3 ceramics sintered at 1200°C exhibited excellent dielectric properties: Q × f value = 80 476 GHz (at 7.681 GHz), εr = 24.7, τf = +3.2 ppm/°C. We also designed two ceramic systems in the Li‐rich region of the Li2O–MgO–TiO2 ternary system, which received little attention in the past decades, because many excellent single‐phase ceramics, such as Li2MgTiO4, Li2MgTi3O8 and MgTiO3, have been found in the Ti‐rich region. The ceramic systems have low sintering temperatures but also relatively poor dielectric properties.

Low-loss dielectric ceramic materials and their properties

In addition to the constant demand of low-loss dielectric materials for wireless telecommunication, the recent progress in the Internet of Things (IoT), the Tactile Internet (fifth generation wireless systems), the Industrial Internet, satellite broadcasting and intelligent transport systems (ITS) has put more pressure on their development with modern component fabrication techniques. Oxide ceramics are critical for these applications, and a full understanding of their crystal chemistry is fundamental for future development. Properties of microwave ceramics depend on several parameters including their composition, the purity of starting materials, processing conditions and their ultimate densification/porosity. In this review the data for all reported low-loss microwave dielectric ceramic materials are collected and tabulated. The table of these materials gives the relative permittivity, quality factor, temperature variation of the resonant frequency, crystal structure, sintering temperature, measurement frequency and references. In addition, the methods commonly employed for measuring the microwave dielectric properties, important from the applications point of view, factors affecting the dielectric loss, methods to tailor the dielectric properties and materials for future applications, are briefly described. The data will be very useful for scientists, industrialists, engineers and students working on current and emerging applications of wireless communications.

Effect on structural, optical and dielectric properties of mixed (1 − x)ZnFe2O4–xSiO2 as microwave dielectric ceramic material

Samples of (1 − x)ZnFe2O4–xSiO2 with different compositions have been prepared using sol–gel method. The morphological structures of the samples were analyzed using AFM and XRD analysis. AFM images show the surface roughness of the produced samples and indicate the surface roughness increased as the compositions of x increased where the average surface roughness to be around 0.30–1.34 nm. XRD analysis indicates the phase formation of cubic structure where dominant peak has been observed with Miller indices (311) at 35.25°. The average crystallite size, D for dominant peak has been calculated with average size to be around ~10 nm. The FTIR analysis indicates the formation of spinel structure for ZnFe2O4 and also the presence of H2O molecules inside the samples. The fabricated patch antenna for samples (x = 0.05, 0.15 and 0.25) gives a good response in return loss analysis which are (>−10 dB).

A New Rapid Detection of the Temperature Coefficient System

The temperature coefficient of the microwave dielectric ceramic materials is one of the important dielectric property parameters. A new method, which can detect the temperature coefficient of microwave dielectric ceramic material, is presented in this article. The test method and software buildup of the system are also introduced. The new system has the advantage in obtaining fast, reliable and high accuracy measurement performance.

Microwave Dielectric Properties of (Ba0.1Mg0.9)(A0.05Ti0.95)O3 (A = Zr, Sn) Ceramics

Microwave dielectric ceramic materials based on (Ba0.1Mg0.9)(A0.05Ti0.95)O3 (A = Zr, Sn) were synthesized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their microwave dielectric properties were investigated. In the system, the substitution Zr and Sn for Ti is effective for dielectric constant and Q × f values up to 73,000 (GHz). Two Ba2Ti9O20 and BaTi5O11 second phases formed and significantly affected the microwave dielectric properties. With Zr and Sn additives, the densification temperature of (Ba0.1Mg0.9)(A0.05Ti0.95)O3 (A = Zr, Sn) ceramics can be effectively reduced to1210°C. The dielectric constant of (Ba0.1Mg0.9)(Zr0.05Ti0.95)O3 (hereafter referred to as BMZT) sintered at 1210°C/4h is 20.6, the Q × f value is 112,000GHz and the temperature coefficient of resonant frequency (τ f ) is -50 ppm/°C. (Ba0.1Mg0.9)(Sn0.05Ti0.95)O3 (hereafter referred to as BMST) sintered at 1210°C/4h has ϵr of 20.4, Q × f value of 73,000 GHz and τ f of −61.5 ppm/°C.

Microwave dielectric properties of CeO 2–0.5AO–0.5TiO 2 (A = Ca, Mg, Zn, Mn, Co, Ni, W) ceramics

Microwave dielectric ceramic materials based on cerium [CeO 2–0.5AO–0.5TiO 2 (A = Mg, Zn, Ca, Mn, Co, Ni, W)] have been prepared by a conventional solid state ceramic route. The crystal structure was studied by X-ray diffraction, microstructure by scanning electron microscopy (SEM) techniques and the phase composition was studied using energy dispersive X-ray analysis (EDXA). The sintered ceramics had a relative dielectric constant ( ɛ r) in the range 17–65 and quality factor Q u xf up to 50,000 GHz and a temperature variation of resonant frequency ( τ f) ranging from a negative value (−62 ppm/°C) to a high positive value (+399 ppm/°C). The majority of the synthesized ceramics were of a two phase composite consisting of a fluorite CeO 2 and perovskite ATiO 3 phase. The microwave dielectric properties were further tailored by adding various amounts of dopants of different valencies to the calcined powder. This made it possible to either tune τ f to zero or improved the quality factor further.

Structures and dielectric properties of a new dielectric material system xMgTiO 3–(1− x)MgTa 2O 6 at microwave frequency

Crystal structure and the microwave dielectric properties of xMgTiO 3–(1− x)MgTa 2O 6 sintered specimens with x = 0.3, 0.5, 0.7 are investigated. The X-ray diffraction patterns revealed the sintered specimens are mixed phases of MgTiO 3, MgTa 2O 6 and MgTi 2O 5. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. With x = 0.7, a new microwave dielectric ceramic material 0.7MgTiO 3–0.3MgTa 2O 6 at 1460 °C for 3 h is suggested for microwave device and it possesses excellent dielectric properties; a dielectric constant ɛ r ∼ 23, a Q × f value ∼81,000 GHz and a τ f value ∼−2 ppm/°C. The correlation between microwave dielectric properties and the microstructures is also discussed.

Improved high Q value of CaTiO 3–Ca(Mg 1/3Nb 2/3)O 3 solid solution with near zero temperature coefficient of resonant frequency

The crystal structures and the microwave dielectric properties of (1−x)CaTiO 3–xCa(Mg 1/3Nb 2/3)O 3 perovskite ceramic system have been investigated. (1−x)CaTiO 3–xCa(Mg 1/3Nb 2/3)O 3 solid solution exhibited orthorhombic crystal structures for all compositions. With x = 0.66, a new microwave dielectric ceramic material 0.34CaTiO 3–0.66Ca(Mg 1/3Nb 2/3)O 3 applicable to microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε r ∼ 48, a Q×f values ∼ 32,500 (at 6.7 GHz) and a τ f value ∼−2 ppm/°C at 1450°C for 3 h. Further improvement of the Q×f value can be achieved by extending the sintering time to 6 h. It reveals a higher Q×f value of 34,000 (at 6.7 GHz) without degrading other microwave dielectric properties of 0.34CaTiO 3–0.66Ca(Mg 1/3Nb 2/3)O 3 ceramics.