Design, Fabrication, and Characterization of a Wideband 60 GHz Bandpass Filter Based on a Flexible PerMX Polymer Substrate

This paper presents a wideband 60 GHz bandpass filter fabricated on a flexible PerMX polymer substrate. A conventional parallel-coupled half-wavelength resonator filter is selected as an embedded passive device. A narrow gap of 5 mu m between 750-mu m-long resonators is successfully fabricated thanks to a Si support substrate. Surface modification is used to release the flexible polymer substrate from the Si substrate after the filter fabrication. A wideband filter is achieved through the optimization of the narrow gaps between the adjacent resonators. The designed filters are implemented in two different types, without a cover and with a cover. The filter without a cover shows an insertion loss of 4 dB at the center frequency of 63.5 GHz and a return loss of better than 10 dB including two CPW pads, while the filter with a cover has an insertion loss of 3.8 dB at 59 GHz and a return loss of better than 13 dB. In addition, the uncovered filter has a 3-dB bandwidth of 24% at 63.5 GHz, while the covered filter shows 28% at 59 GHz.