Characterization of A6 LTCC Systems for Microwave and Millimeter-Wave Applications

Low Temperature Co-fired Ceramic (LTCC) materials are widely used in ceramic packaging and interconnect applications, such as RF receiving modules for next generation handsets and T/R modules for satellite communications. The application frequency spans from low GHz to 100+ GHz. A variety of techniques must be used to characterize dielectric properties (loss tangent and dielectric constant) of LTCC in the wide frequency range. These techniques include the parallel plate capacitor method from DC to several MHz, cavity methods in x-band, and open resonator techniques for frequencies up to 100+ GHz. LTCC is a multi-layer ceramic technology, which offers capability for low cost manufacturing, realizing 3D structures, and embedding passive components. Both strip line and microstrip types of transmission line structures can be conveniently manufactured using LTCC material systems. As an important performance parameter, microstrip loss can be characterized using the ring resonator technique. Both LTCC and metal conductors contribute to the microstrip loss. At microwave and mm-wave frequencies, metal losses become significant, although low resistance silver conductor can be used. The metal loss may be divided into two categories: one is the resistive loss and other is surface roughness loss. A photo imaging technique has been introduced which patterns the microstrip, reducing the surface loss. In this paper, the techniques for measuring both dielectric properties of A6 LTCC and microstrip properties of A6 LTCC with conductor systems will be reviewed. Characterization results of the dielectric constant and loss tangent of A6 from near DC to 100 GHz will be presented. Microstrip losses, measured for A6 LTCC with both gold and silver metallization up to 40 GHz, are compared to those computed using the closed form equations and experimentally determined dielectric and conductor properties. The calculated effective microstrip permitivity and attenuation compare well to those from measurements.