A Millimeter-Wave Substrate Integrated Waveguide Filter in Si-BCB Technology

In this paper the design, measurements and retro-simulations of a 110-GHz 5th-order Chebyshev filter, based on substrate integrated waveguide in a 30-mu m thick BenzoCycloButene (BCB) above-IC technology, are presented. A center frequency of 101.5 GHz, corresponding to a 8.5-GHz frequency shift towards low frequencies, and 11.8% of fractional bandwidth are measured. The filter presents 4.6-dB of insertion loss and a low return loss of 17.5 dB in the passband. Thanks to optical profilometer measurements, a deformation of the top metallic cover of the SIW structures was observed. Electromagnetic simulations taking this top surface deformation into account allows recovering the measured filter behaviour with the center frequency shift. Thus, this BCB above-IC technology seems promising for the design of passive circuits at higher frequencies, at which substrate heights of 30 mu m are more appropriate.