Low-loss and ultra-low temperature sintering microwave dielectrics of pure and Ag-modified K2Mg2(MoO4)3 ceramics

Novel K_2–2xAg_2xMg₂(MoO₄)₃ (x = 0–0.09) ceramics were synthesized by conventional solid-state sintering method. Based on the X-ray diffraction (XRD) patterns, all samples were identified to belong to an orthorhombic structure with a space group of P212121(19). The pure phase K₂Mg₂(MoO₄)₃ specimen when sintered at 590 °C revealed the favorable microwave dielectric properties: ε_r of 6.91, Q×f of 21,900 GHz and τ_f of ?164 ppm/°C. The substitution of Ag⁺ for K⁺ in K_2–2xAg_2xMg₂(MoO₄)₃ (x = 0.01–0.09) ceramics led to the more stable structure and dramatically enhanced the Q×f to a value of 54,900 GHz at 500 °C. The microwave dielectric properties were related to the relative density, microstructure, ionic polarization, lattice energy, packing fraction, and bond valence of the ceramics. It was suggested that for ultra-low temperature co-fired ceramic (ULTCC) applications, K_1.86Ag_0.14Mg₂(MoO₄)₃ ceramic could be sintered at 500 °C, which revealed an excellent combination of microwave dielectric properties (ε_r =7.34, Q×f =54,900 GHz and τ_f =–156 ppm/°C) and good chemical compatibility with aluminum electrodes.     

The dielectric,thermal properties and crystallization mechanism of Li–Al – B–Si – O glass – Ceramic systems as a new ULTCC material

Li–Al–B–Si–O (LABS) glass-ceramics with a sintering temperature of 600 °C were studied for ultra-low temperature co-fired ceramics (ULTCC) applications. The crystal phase of LABS glass-ceramics is dendritic β-spodumene. The permittivity and dielectric loss of LABS glass-ceramics are ε_r = 5.8 and tgδ = 1.3 × 10⁻³ at 10 MHz, respectively. The coefficient of thermal expansion (CTE) of LABS glass-ceramics is 3.23 ppm/°C, which is close to that of silicon. The dielectric and thermal properties of LABS glass-ceramics are closely correlated to the degree of its crystallization. The permittivity decreases continually while the dielectric loss decreases first and slightly increases with the increasing of crystallization of β-spodumene. The CTE of LABS glass-ceramics decreases as β-spodumene crystallized from LABS glass. The crystallization kinetic and mechanism of LABS glass-ceramics indicate that the β-spodumene crystallizes in a two-dimensional interfacial growth mechanism due to the migration of Li-ions. The diffusion coefficients derived from energy-dispersive X-ray spectroscopy (EDS) results indicated that both Al and Ag electrodes have good compatibilities with ULTCC tapes, which could reduce the cost of multilayer electro-ceramic devices dramatically by using the ULTCC and base metallization.     

Effect of Mn:Mg ratio on sintering behavior and microwave dielectric properties of (Mn,Mg)V2O6 ceramics at ultra-low sintering temperature

Ultra-low-firing-temperature ceramics (Mn_1−xMg_x)V₂O₆ (x = 0–1) were prepared using the conventional solid-state reaction method. The effects of the Mn:Mg ratio on the crystal structure and microwave dielectric properties of the prepared ceramics were systematically investigated. The results indicated that an appropriate Mn:Mg ratio effectively improves the dielectric properties of the compounds. Specimens with x = 0.01 and x = 0.93 sintered at 630 °C exhibited the following microwave dielectric properties: ε_r = 12.4 and 9.8, high Q×f = 57,000 and 21,000 GHz, and τ_f = –15 and −24 ppm/°C, respectively. This suggests that the (Mn_0.99Mg_0.01)V₂O₆ ceramic is a potential material for ULTCC applications.     

High-performance microwave dielectric glass-ceramic with fine secondary structure for ULTCC application

x ZnO- (100-x) B₂O₃ (x = 45–64 mol%) glass-ceramics for ULTCC applications were prepared via the solid-state reaction method, and their crystallization behavior, sintering mechanism, microstructure and microwave dielectric properties were investigated. In this work, the zinc boron binary glasses can be formed in the range of 45–73 mol% ZnO content, and the glass with 55 mol% ZnO content has the highest glass-forming ability. The Zn₄B₆O₁₃ crystal is formed in binary ZnO-B₂O₃ glass at 640 °C, which is much lower than that in ceramics. The glass-ceramics exhibit large grains with 5 ～ 10 µm consisting of fine and uniform secondary structures. The precipitation of Zn₄B₆O₁₃ crystal and the refinement secondary structure improves the microwave dielectric properties. The 55 ZnO - 45 B₂O₃ glass-ceramic sintered at 640 °C for 5 h exhibits the optimum microwave dielectric properties of ε_r = 6.09, Q×f = 20,389 GHz, τ_f = 14 ppm/°C, and also high Vickers hardness of 625 kgf/mm² and good chemical compatibility with Ag or Al electrode, which is a good candidate for ULTCC substrate materials.     

Heterogeneous multilayer dielectric ceramics enabled by ultralow-temperature self-constrained sintering

In the present work, heterogeneous multilayer ceramics based on two representative dielectrics, low-K Li₂MoO₄ (LM) and high-K [(Li_0.5Bi_0.5)_xBi_1−x][Mo_xV_1−x]O₄ (LBMV), are successfully acquired using a convenient approach of self-constrained sintering at an ultralow temperature of 600°C. These two materials with proximate but distinct sintering temperature ranges mutually act as constrained layers to each other in the process of densification, yielding significantly suppressed in-plane shrinkage of the LM/LBMV heterogeneous multilayer ceramics. Moreover, the dense heterostructures are endowed with decent mechanical and microwave dielectric properties. This work offers a new paradigm for facilely integrating heterogeneous dielectric materials for ultralow-temperature co-fired ceramics applications.     

Sintering behavior,structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li_2xCu_1-xMoO₄ (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li⁺ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu⁺ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A_1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li_2xCu_1-xMoO₄ ceramic sintered at 675 °C exhibited optimal comprehensive properties with ε_r = 8.17, Qf = 68 476 GHz, and τ_f = ?25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li_2xCu_1-xMoO₄ (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.     

Anodic bondable Li-Na-Al-B-Si-O glass-ceramics for Si - ULTCC heterogeneous integration

In this paper, we report an anodic bondable Li-Na-Al-B-Si-O (LNABS) glass-ceramic system with a low temperautre (150 °C) and voltage (200 V) for Si - ULTCC (Ultra-Low Temperature Co-fired Ceramics) heterougeneous integration. The ULTCC materials are predominantly composed of multicrystalline LiAlSi₂O₆ with a small amount of glass phase. The coefficient of thermal expansion (CTE) of LNABS is 3.27 ppm/°C (25–300 °C) leading to excellent theraml compatibility with silicon wafer over a wide temperature range from 60 °C to 300 °C. To demonstrate the utility of this system, a silicon micro-electro-mechanical (MEMS) systems pressure sensor is encapsulated between silicon and ULTCC substrates. This sensor exhibits high accuracy and good stability in the temperature range from ?40 °C to 120 °C. The bonding current, cross section and alkali ions concentration were investigated, and the anodic bonding mechanism at low temperature and voltage was revealed. The alkali ions migrate through the glass phase due to its lower activation energy, which also forms a high space-charge electric field at the bonding interface. The non-bridge oxygen (NBO) drifts towards silicon and oxidized silicon under high space-charge electric field. The calculated diffusion coefficient of NBO indicates that the elevated temperature and voltage both benefit the migration of NBO. These finding illustrate the great potential of LNABS glass-ceramic for high quality microelectronic and MEMS packaging technology with advantages of multilayer structure, low anodic bonding temperature and voltage, as well as the excellent theraml compatibility with Si wafers.     

Enhanced Na+-substituted Li2Mg2Mo3O12 ceramic substrate based on ultra-low temperature co-fired ceramic technology for microwave and terahertz polarization-selective functions

A novel Li₂Mg_2-xNa_2xMo₃O₁₂ (x = 0.09) ceramic with ultra-low sintering temperature is prepared by the solid-state reaction method. This ceramic (625 °C) exhibits excellent microwave dielectric properties (ε_r = 7.9, Q×f = 43844 GHz, τ_f = ?48.3 ppm/°C), terahertz transmission properties (ε_r¹ = 7.4, tan σ¹ = 0.0158, T_coefficient = 0.598), and chemical compatibility with Ag. For the first time, two polarization selective devices are designed in the microwave and terahertz regions by using this ceramic substrate, respectively. The transmission amplitudes of the right- and left-handed circularly polarized waves of the microwave device at 9.7 GHz are 0.895 and 0.019, respectively. The transmission coefficients of the y- and x-polarized waves of the terahertz device at 0.45 THz are 0.598 and 0.075, respectively. Both functions are verified by the overall far-field radiation pattern. This work promotes the application of dielectric ceramics and ULTCC technology in the microwave and terahertz regions.     

Sintering behavior,structure and dielectric properties of CuO-ZnO-MgO-B2O3 glass-ceramics for ULTCC applications

High performance ultra-low temperature co-fired ceramic (ULTCC) materials were prepared from CuO- MgO- ZnO- Al₂O₃- B₂O₃- Li₂O glass-ceramics. The sintering behaviors, crystalline phase evolution, microstructure and dielectric properties, as well as their compatibility with Ag and Al electrodes, were investigated. With the suitable substitution of MgO for ZnO, the dielectric properties of glass-ceramics were improved. It is mainly associated with the fine microstructure, highly crystallinity, and decrease in tetrahedral distortion in the crystal lattice. All the glasses completed the densification at 575–600 °C, and ZnB₄O₇ is the only crystalline phase precipitated from the glasses. Moreover, the glass-ceramic with 1 wt% MgO sintered at 575 °C for 5 h, exhibited low relative permittivity ~ 7.1 and low dielectric loss ~ 6.40 × 10^?4. And the glass-ceramic with 4 wt% MgO sintered at 600 °C for 5 h, also displayed low relative permittivity ~ 7.1 and low dielectric loss ~ 5.77 × 10^?4. Both two glasses have good sintering compatibility with silver and aluminum electrodes, which provided high potential for ULTCC application.