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In developing low-temperature cofired ceramic (LTCC) technology for high-density packaging or advanced packaged electronics, matching the coefficient of thermal expansion (CTE) among the packaged components is a critical challenge to improve reliability. The CTEs of solders and organic laminates are usually larger than 16.0 ppm of °C 1- , while most low-permittivity (ε r ) dielectric ceramics have CTEs of less than 10.0 ppm °C 1- . Therefore, a good CTE match between organic laminates and dielectric ceramics is required for further LTCC applications. In this paper, we propose a high-CTE BaSO 4 -BaF 2 LTCC as a potential solution for high-reliability packaged electronics. The BaSO 4 -BaF 2 ceramics have the advantages of a wide low-temperature sintering range (650-850 °C), low loss, temperature stability, and Ag compatibility, ensuring excellent performance in LTCC technology. The 95 wt %BaSO 4 -5 wt %BaF 2 ceramic has a ε r of 9.1, a Q × f of 40,100 GHz @11.03 GHz ( Q = 1/tan δ), a temperature coefficient of the resonant frequency of -11.2 ppm °C 1- , a CTE of +21.8 ppm °C 1- , and a thermal conductivity of 1.3 W mK -1 when sintered at 750 °C. Furthermore, a dielectric resonant antenna using BaSO 4 -BaF 2 ceramics, a typically packaged component of LTCC and laminate, was designed and used to verify the excellent performance by a gain of 6.0 dBi at a central frequency of 8.97 GHz and a high radiation efficiency of 90% over a bandwidth of 760 MHz. Good match and low thermal stress were found in the packaged components of BaSO 4 -BaF 2 ceramics, organic laminates, and Sn-based solders by finite element analysis, proving the potential of this LTCC for high-reliability packaged electronics.

Vanadium(V)-substituted cerium niobate [Ce(Nb 1- x V x )O 4 , CNV x ] ceramics were prepared to explore their structure-microwave (MW) property relations and application in C-band dielectric resonator antennas (DRAs). X-ray diffraction and Raman spectroscopy revealed that CNV x (0.0 ≤ x ≤ 0.4) ceramics exhibited a ferroelastic phase transition at a critical content of V ( x c = 0.3) from a monoclinic fergusonite structure to a tetragonal scheelite structure (T F-S ), which decreased in temperature as a function of x according to thermal expansion analysis. Optimum microwave dielectric performance was obtained for CNV0.3 with permittivity (ε r ) of ∼16.81, microwave quality factor ( Qf ) of ∼41 300 GHz (at ∼8.7 GHz), and temperature coefficient of the resonant frequency (TCF) of ∼ -3.5 ppm/°C. ε r is dominated by Ce-O phonon absorption in the microwave band; Qf is mainly determined by the porosity, grain size, and proximity of T F-S ; and TCF is controlled by the structural distortions associated with T F-S . Terahertz (THz) (0.20-2.00 THz, ε r ∼ 12.52 ± 0.70, and tan δ ∼ 0.39 ± 0.17) and infrared measurements are consistent, demonstrating that CNV x (0.0 ≤ x ≤ 0.4) ceramics are effective in the sub-millimeter as well as MW regime. A cylindrical DRA prototype antenna fabricated from CNV0.3 resonated at 7.02 GHz (| S 11 | = -28.8 dB), matching simulations, with >90% radiation efficiency and 3.34-5.93 dB gain.