Glass-free low-temperature cofired ceramics: calcium germanates, silicates and tellurates

TLDR: In this article, a basic characterization of several low-temperature-sintered calcium silicates, germanates and tellurates was performed to evaluate their potential as glass-free low-permittivity substrate LTCC materials.

Abstract: To reduce the complexity of LTCC systems, and so accelerate the development of LTCC tapes with new functionalities, it is necessary to reduce the number of phases within a particular tape. This can best be done by using glass-free single-phase ceramic systems. We performed a basic characterization of several low-temperature-sintered calcium silicates, germanates and tellurates in order to evaluate their potential as glass-free low-permittivity substrate LTCC materials. Special attention was focused on their microwave and 1 MHz dielectric properties, their sintering behavior and their compatibility with Ag. Two Ca-germanates, which were found to be the most interesting for LTCC applications exhibit a permittivity of ∼10 and low dielectric losses; however, the temperature dependence of permittivity and the sintering temperature must be further reduced. For CaGeO3 the temperature dependence of permittivity was fully suppressed by the addition of 10 mol% of CaTiO3.