Development of a low-temperature sintered dielectric material derived from Li2MgSiO4 (LMS) for low-temperature cofired ceramic (LTCC) application is discussed in this paper. The LMS ceramics were prepared by the solid-state ceramic route. The calcination and sintering temperatures of LMS were optimized at 850°C/4 h and 1250°C/2 h, respectively, for the best density and dielectric properties. The crystal structure and microstructure of the ceramic were studied by the X-ray diffraction and scanning electron microscopic methods. The microwave dielectric properties of the ceramic were measured by the cavity perturbation method. The LMS sintered at 1250°C/2 h had ɛr=5.1 and tan δ=5.2 × 10−4 at 8 GHz. The sintering temperature of LMS is lowered from 1250°C/2 h to 850°C/2 h by the addition of both lithium borosilicate (LBS) and lithium magnesium zinc borosilicate (LMZBS) glasses. LMS mixed with 1 wt% LBS sintered at 925°C/2 h had ɛr=5.5 and tan δ=7 × 10−5 at 8 GHz. Two weight percent LMZBS mixed with LMS sintered at 875°C/2 h had ɛr=5.9 and tan δ=6.7 × 10−5 at 8 GHz.

Low‐Temperature Sintering and Microwave Dielectric Properties of Li2MgSiO4 Ceramics

The crystal structure, microstructure, and microwave dielectric properties of forsterite-based (Mg1–xNix)2SiO4 (x = 0.02–0.20) ceramics were systematically investigated. All samples present a single forsterite phase of an orthorhombic structure with a space group Pbnm except for a little MgSiO3 secondary phase as x > 0.08. Lattice parameters in all axes decrease linearly with increasing Ni content due to the smaller ionic radius of Ni2+ compared to Mg2+. The substitution of an appropriate amount of Ni2+ could greatly improve the sintering behavior and produce a uniform and closely packed microstructure of the Mg2SiO4 ceramics such that a superior Q × f value (152 300 GHz) can be achieved as x = 0.05. The τf value was found to increase with increasing A-site ionic bond valences. In addition, various additives were used as sintering aids to lower the sintering temperature from 1500°C to the middle sintering temperature range. Excellent microwave dielectric properties of er~6.9, Q × f~99800 GHz and τf~−50 ppm/°C can be obtained for 12 wt% Li2CO3-V2O5-doped (Mg0.95Ni0.05)2SiO4 ceramics sintered at 1150°C for 4 h.

Structure‐Dependent Microwave Dielectric Properties and Middle‐Temperature Sintering of Forsterite (Mg1–xNix)2SiO4 Ceramics

The explosive process of 5G communication evokes the urgent demand of miniaturized and integrated dielectric ceramics filter. It is a pressing need to advance the development of dielectric ceramics utilization of emerging technology to design new materials and understand the polarization mechanism. This review provides the summary of the study of microwave dielectric ceramics (MWDCs) sintered higher than 1000 from 2010 up to now, °C with the purpose of taking a broad and historical view of these ceramics and illustrating research directions. To date, researchers endeavor to explain the structure-property relationship of ceramics with multitude of approaches and design a new formula or strategy to obtain excellent microwave dielectric properties. There are variety of factors that impact the permittivity, dielectric loss, and temperature stability of dielectric materials, covering intrinsic and extrinsic factors. Many of these factors are often intertwined, which can complicate new dielectric material discovery and the mechanism investigation. Because of the various ceramics systems, pseudo phase diagram was used to classify the dielectric materials based on the composition. In this review, the ceramics were firstly divided into ternary systems, and then brief description of the experimental probes and complementary theoretical methods that have been used to discern the intrinsic polarization mechanisms and the origin of intrinsic loss was mentioned. Finally, some perspectives on the future outlook for high-temperature MWDCs were offered based on the synthesis method, characterization techniques, and significant theory developments.

/pdf/the-latest-process-and-challenges-of-microwave-dielectric-2ikdizak8f.pdf

The latest process and challenges of microwave dielectric ceramics based on pseudo phase diagrams

Microwave dielectric properties of Li2TiO3 ceramics doped with LiF for LTCC applications

Structure/property regulation is widely investigated for providing theoretical foundations and guidance for designing microwave dielectric ceramics. P–V–L bond theory targets the provision of detailed structural parameters of crystals and fundamental chemical bond characteristics, such as bond ionicity, bond covalency and bond susceptibility. In this review, the concept of P–V–L bond theory, the binary bonding formula theory of complex polycrystalline and the usage of P–V–L bond theory regarding the structural effects on dielectric properties in various crystal structures are introduced. And the bond traits provided via P–V–L bond theory in several ion-doping modification systems are generalized with structural evolution and dielectric properties. Furthermore, conjectures about the development and application directions of P–V–L bond theory in the study of structure/properties of microwave dielectric ceramics are put forward.

Usage of P–V–L bond theory in studying the structural/property regulation of microwave dielectric ceramics: a review

Synthesis and microwave dielectric properties of CaSiO3 nanopowder by the sol–gel process

A low-permittivity microwave dielectric ceramic system (Ca 1− x Mg x ) SiO 3 was investigated. The effects of Mg and Ca substitutions in the A-site on the crystal structure and microwave dielectric properties were studied. Specimens with compositions of x  = 0.1, 0.5 and 0.9 were single-phased. The secondary phases that decrease the Qf values were observed in specimens with other compositions. Single-phased ceramics had relatively higher Qf values. When x  = 0.1, the specimen sintered at 1290 °C for 2 h exhibited excellent properties of ɛ r  = 6.49, Qf  = 62,420 GHz and τ f  = −43.3 ppm/°C.

(Ca1−xMgx)SiO3: A low-permittivity microwave dielectric ceramic system

A new low-temperature microwave dielectric ceramic with low-permittivity was found and investigated in the CaO–MgO–SiO2–TiO2 system. Phase constitutes and dielectric properties of (Ca1−x,Mgx)SiO3 (x = 0.1–0.5) ceramics were studied with different x contents, and CaTiO3 demonstrated an effective compensation in (Ca1−x,Mgx)SiO3 τf value. The 0.88CaMgSi2O6–0.12CaTiO3 compositions show a relatively low-permittivity (∼9.42), high Q × f values up to 52,800 GHz, and near-zero temperature coefficients (5.6 ppm/°C), which were obtained via sintering at 1300 °C. The addition of ≤2.0 wt% Li2CO3–V2O5 was very effective in lowering the sintering temperature (Ts), and dense ceramics could be obtained at Ts ≤ 900 °C. The addition of Li2CO3–V2O5 does not induce apparent degradation in the microwave properties. The specimens with 1 wt% Li2CO3–V2O5 sintered at 880 °C for 2 h shows excellent dielectric properties: ɛr = 9.23, Q × f = 46,200 GHz, and τf = 1.3 ppm/°C. The low-temperature sintering ceramics powders were suitable for the tape casting process. Also, the material is compatible with Ag electrodes, and therefore, is suitable for LTCC application.

A new microwave ceramic with low-permittivity for LTCC applications

Silver cofirable (Ca0.9, Mg0.1)SiO3 microwave dielectric ceramics with Li2CO3–Bi2O3 additive

The effects of CuO and TiO2 additives on the microstructure and microwave dielectric properties of Al2O3 ceramics were investigated. Al2O3 ceramics with CuO and TiO2 additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti4Cu2O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO2 content, due to the formation of the second phase Ti4Cu2O. However, the varying behaviors of the dielectric constant (ɛr) and temperature coefficients (τf) were associated with phase constitutions, as a result of the change of CuO and TiO2content. The τf can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO2. The specimens with 0.5 wt.% CuO and 7 wt.% TiO2 sintered at 1,360 °C for 4 h showed ɛr of 11.8, Qf value of 30,000 GHz, and τf of −7 ppm/°C.

Huiping Sun

Papers

Synthesis and microwave dielectric properties of CaSiO3 nanopowder by the sol–gel process

(Ca1−xMgx)SiO3: A low-permittivity microwave dielectric ceramic system

A new microwave ceramic with low-permittivity for LTCC applications

Silver cofirable (Ca0.9, Mg0.1)SiO3 microwave dielectric ceramics with Li2CO3–Bi2O3 additive

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO