Innovative dielectric materials at millimeter-frequencies

The need of low-loss substrate materials with stable dielectric performances over a wide frequency range is a strong requirement when working at millimeter frequencies, where standard dielectric substrates exhibit prohibitive losses. In this contribution, the authors focus their attention on a polymer material, the benzocyclobutene (BCB), having a low dielectric constant equal to 2.65, and a low loss tangent, equal to 0.0008 at 1 GHz, with a stable dielectric behavior over a broad frequency range, up to THz. The use of BCB is proposed here as innovative dielectric substrate for millimeter-wave printed circuits. At this purpose, an accurate dielectric characterization of BCB is firstly performed up to 65 GHz to demonstrate the low-loss and stable behavior of the material. Measurements of dielectric parameters are executed on test circuits, which are realized on BCB substrate by a in-house fabrication technology able to produce BCB substrate of arbitrary thicknesses. The developed BCB fabrication technology is applied to the design and realize a 60 GHz microstrip reflectarray.