Bulk and In-Circuit Dielectric Characterization of LTCC Tape Systems Through Millimeter Wave Frequency Range

摘要

Low Temperature Co-fired Ceramic (LTCC) material systems offer a highly versatile microwave and millimeterwave packaging platform. Extremely low microwave loss, excellent control of dielectric constant, uniform dielectricthickness, non-existent water absorption leading to very high hermeticity, ability to support multilayer structureleading to 3-dimensional packaging, ability to embed passive functions within the tape layers, availability of a widerange of metallizations, etc. are some of the key advantages of LTCC for microwave packaging. One of theimportant parameters which needs to be determined at the very early stages of circuit designs are the dielectricproperties - dielectric constant and loss tangent, both of which are functions of frequency. These properties need tobe known accurately over the entire frequency range of operation for the circuit. For LTCC based designs, the use ofdielectric constant of bulk material can lead to deviations between the performance expected at the design stage andfor the fabricated circuit. Such deviations are a significant concern for broadband circuits as well as for circuits withsharp resonant behavior such as filters. One of the significant sources of deviation between bulk LTCC and “incircuit”dielectric constant is the nature of the thick film metallizations used in LTCC technology. Work describedhere is a comprehensive characterization of three DuPont? GreenTape? LTCC systems 951, 943, and 9K7 - in thefrequency range 10 to 70 GHz. Both bulk and “in-circuit” dielectric properties with silver and gold metallizationsare studied to quantify the deviations in dielectric properties. A Fabry-Perot open resonator technique is used for thebulk characterization while printed ring resonators are used for the in-circuit characterization. This comprehensivecharacterization will provide key design data for LTCC designers in the 10 – 70 GHz frequency range.