Variable dielectric constants by structured porosity for passive ceramic components

Abstract

In this paper, different densities within a ceramic are used to provide a wide, continuous range of cofirable dielectric constants for high frequency applications. Cofiring different ceramic materials together to make a single, unified structure to obtain different dielectric constant combinations is quite difficult due to phase stability issues and shrinkage mismatches. However, using various levels of porosity in order to alter the effective dielectric constant in the same material allows cofiring of different dielectric constants into a single unit. Since the structure is made from a single material, the varying porosities can be made compatible. Large scale aligned porosity using a microcellular structure allows for an extremely wide range of dielectric constants, ranging from 90 to 9.15, while maintaining a low loss tangent. Examples using the cofiring of the different density ceramics include a stratified medium cavity resonator and a buried dielectric resonator internal to a microcellular substrate.