MSO₄ (M = Ca, Sr, Ba) microwave dielectric ceramics with low dielectric constant

Abstract

MSO 4 (M = Ca, Sr, Ba) ceramics with relative densities exceeding 96% were prepared by solid-state sintering at low sintering temperatures of 625-875 • C, and their structures and microwave dielectric properties at 10-19 GHz were characterized. MSO 4 ceramics crystallized in orthorhombic symmetry with the space groups of Amma for CaSO 4 and Pnma for SrSO 4 and BaSO 4 . The optimal microwave dielectric properties were obtained with ε r = 5.85, Qf = 57 000 GHz, τ f,W = −98.8 ppm/ • C for CaSO 4 , ε r = 10.95, Qf = 15 500 GHz, τ f,W = 101.6 ppm/ • C for SrSO 4 , and ε r = 9.42, Qf = 38 200 GHz, τ f,W = −4.7 ppm/ • C for BaSO 4 . The increased ε r and τ f,W while decreased Qf value in the order of CaSO 4 , BaSO 4 , and SrSO 4 were attributed to the enhanced rattling effect of M 2+ . Besides, the temperature dependence of τ f was weak for CaSO 4 and BaSO 4 , whereas much stronger for SrSO 4 . As most low-ε r microwave dielectric ceramics are of large negative τ f , the near-zero τ f of BaSO 4 and positive τ f of SrSO 4 are rare, indicating they are potential candidates for millimeter-wave communication as a temperaturestable dielectric ceramic and a compensator for tuning negative τ f to near-zero, respectively.

Mg/Ti co‐substituted CaSmAlO4‐based microwave dielectric ceramics with temperature stability in a wide temperature range

“…Meanwhile, τ f of microwave dielectric ceramics is usually regarded as a constant independent of temperature over a wide temperature range, whereas in reality τ f strongly depends on temperature and even changes positively or negatively with temperature. Therefore, measuring the resonant frequency at two temperature points only for τ f may lead to errors in the true temperature stability of microwave dielectric ceramics, thus seriously misleading their practical applications 3,4,40 . So it is necessary to study τ f in two or more temperature ranges.…”

“…Therefore, measuring the resonant frequency at two temperature points only for τ f may lead to errors in the true temperature stability of microwave dielectric ceramics, thus seriously misleading their practical applications. 3,4,40 So it is necessary to study τ f in two or more temperature ranges. Existing work has confirmed the feasibility of this approach, 8,25,41-…”

Low-Permittivity and Low-Temperature Cofired BaSO4–BaF2 Microwave Dielectric Ceramics for High-Reliability Packaged Electronics

“…14 Therefore, it is still desired to have LTCC materials with high-CTE and excellent dielectric properties for highly reliable packages. Li et al 15 reported that BaSO 4 ceramics had low-ε r , near-zero temperature coefficient of resonant frequency (TCF) and a low sintering temperature of 875 °C. However, there are some differences with regard to our work on BaSO 4 ceramics.…”

Structure evolution and adjustment of τf in (Ba, Sr)HfO3 and (Sr, Ca)HfO3 microwave dielectric ceramics

“…As the key materials for resonators and filters, microwave dielectric ceramics are required to possess an appropriate dielectric constant ε r to balance smaller device size and working frequency, high-quality factor Q to obtain excellent frequency selectivity and near-zero temperature coefficient of resonant frequency τ f to ensure the temperature stability. [1][2][3] Although a number of microwave dielectric ceramics have been developed, [4][5][6] pursuing the optimum combination of these three parameters is still a big challenge. Generally, tuning and improving the Q value and τ f are considered to be the crucial task for obtaining the microwave dielectric ceramics with a specific ε r .…”