Filtering Capacitors Embedded in LTCC Substrates for RF and Microwave Applications

摘要

This article presents a new solution to build filtering capacitors embedded in low temperature co-fired ceramic (LTCC). A new low loss high-k dielectric (K = 80) tape compatible with DuPont low-k tapes has been developed and used in order to demonstrate embedded filter capacitors in LTCC substrates. The BZN powder with the chemical composition Bi_2(Zn_(1/3)Nb_(2/3))_2O_7 was prepared using a conventional ceramic process. Ceramic tapes were prepared by tape casting using the Doctor-Blade technique. Electromagnetic properties of the sintered ceramics and tapes were measured. At 2.9 GHz, the permittivity is 78 with tanδ = 10~(-3). The LTCC manufacturing process was adapted to composite dielectric stacks. LTCC test vehicles including buried filtering capacitors were designed, manufactured and submitted to an evaluation program. The new technology allows a capacitance density of 15 pF/mm~2. Capacitors from 4 pF to 30 pF were characterized in the 300 MHz to 6 GHz frequency range showing satisfactory properties. Embedded, capacitor structures were analyzed with a 3-D EM simulation software and a good agreement with measurements was obtained.