Novel CMOS low-loss transmission line structure

As operating speeds increase low-loss interconnect structures such as transmission lines become critical in the design of RF and high speed digital circuits. This paper presents a novel low-loss transmission line structure. We discuss the importance of transmission line structures, including coplanar and grounded coplanar structures. Grounded coplanar waveguide (GCPW) structures are enhanced to reduce the substrate loss. The primary goal of new interconnect topology, stacked GCPW (S-GCPW), is to reduce the loss by shaping the electric fields under the signal line. 3D electromagnetic wave simulations are used to verify the efficacy of the new transmission line structures. The insertion loss for a 4 mm long S-GCPW structure is 1.62 dB@50 GHz (0.41dB/mm) while the insertion loss for a 4 mm long traditional GCPW structure is 3.28 dB (0.82 dB/mm) in a 0.12 μm SOI CMOS technology.