Slow-wave slot microstrip transmission line and bandpass filter for compact millimetre-wave integrated circuits on bulk complementary metal oxide semiconductor

Abstract

In this study, a novel on-chip low-loss slow-wave slot (SWS) microstrip transmission line is proposed. Unlike conventional slow-wave structures such as photonic bandgap and ladder microstrip transmission line, which usually deal with either the substrate, ground plane or the signal line separately, the periodic patterns of SWS structures are etched along both the conductive metal strip and the ground plane of the microstrip line. The proposed structure, unlike other slow-wave structures does not require extra drilling through the substrate or complex three-dimensional multi-layer structures, only requires coplanar slot etching. The proposed SWS microstrip demonstrates excellent size reduction with minimal increase in loss. To show the utility of the proposed method, two second-order rectangular open-loop filters with and without implementing the proposed SWS microstrip have been designed with similar bandwidths and fabricated in the millimetre-wave (mm-wave) range on 65-nm bulk complementary metal oxide semiconductor (CMOS). Both simulations and measurements demonstrate that the on-chip filter implemented using the proposed SWS has a 52.7% reduction in size while suffering only an additional 0.5 dB in transmission loss penalty. To the best of authors’ knowledge, this compact filter is the first reported mm-wave filter using slow-wave structure on bulk CMOS.