Design of Wideband Functional Via Structures for LTCC Multilayer Substrates up to 110 GHz

A novel concept for designing wideband via structures on low temperature cofired ceramic (LTCC) substrates is presented. In order to achieve wideband behavior, the vias have to be optimized with respect to frequency stability of the characteristic impedance so that the vias may be operated functionally as transmission lines. The characterisitc impedance and phase velocity of the via transition are studied through design space exploration involving critical parameters, i.e. antipad radius, distance to and number of ground vias, and cavity height. Typical LTCC technology constraints are observed in order to ensure manufacturability. Full wave models based on the finite element method (FEM) and finite integration technique (FIT) constitute the main computational tools for analysis and cross-checking of simulation results. Lastly, a sensitivity analysis is conducted to assess the applicability of vias as transmission lines in light of manufacturing tolerances. Parasitic effects due to microstrip or stripline connections are neglected in this work.