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|Highly Integrated Passive LTCC Device with Embedded High-k Capacitors|
|Keywords: LTCC, Passive Integration, Embedded Capacitors|
|One important advantage of embedded elements in LTCC is the free implementation of component values. Designers are not limited to SMD standard EIA decade values like E24, E48 or E96. Integrated passive devices or modules for RF applications (e.g. filters, diplexer etc.) require inductors and capacitors with low manufacturing tolerance and high quality factor. The latter is directly related to the insertion loss characteristic or filter skirt steepness. Tolerances may arise from material variations (vendor lot dependent) and, predominantly, manufacturing steps (screen printing). Parallel plate capacitors are very sensitive to thickness variations of the dielectric layer between electrodes. Therefore, screen printing of high-k-dielectrics is not applicable. LTCC tapes are known for their uniform thickness but suffer also from a low dielectric constant which poses limitations for capacitance values above two Pico farads. Insertion of a full high-k layer is a solution to increase the capacitance density. However, the area not required by the capacitors cannot be used by other structures due to high parasitic influences (e.g. capacitive coupling). Locally inserted high-k patches offer both high capacitance densities and tolerances better than five percent. Furthermore, they do not affect the surrounding layout. The method of local embedding of thin low loss high-k tapes is demonstrated for a four port coupling device operating at about 2.5 GHz. The circuit contains three capacitors and three inductors within an area of 2.4 mm x 2.4 mm. The paper covers design, RF simulation/optimization, manufacturing aspects and measurement results.|
|Jens Mueller, Professor
Ilmenau University of Technology
Ilmenau, Thuringia D-98693,