Sub-THz Substrate Integrated Waveguide Signal Transitions in Backend-of-Line of a Silicon Process

This paper presents a sub-THz substrate integrated waveguide (SIW)-to-microstrip and an SIW-to-grounded coplanar waveguide (GCPW) transition, realized in the backend-of-line (BEOL) of a silicon (Si) process. The transitions are realized in a back-to-back configuration with ground-signal-ground (GSG) pads on both ends to enable probe-based S-parameter measurement. The influence of the GSG probe pads is de-embedded based on the bisection of a Thru structure. The measured and de-embedded S-parameters show good agreement with the simulation results. The measured average insertion loss of the SIW-to-microstrip and SIW-to-GCPW transitions, in the range of 200 GHz to 310 GHz, is 1.2 dB and 0.9 dB, respectively, which represents the lowest insertion loss demonstrated for an on-chip SIW-to-microstrip and SIW-to-GCPW transition to date. In addition, these transitions are implemented with the smallest chip area required for an on-chip SIW-to-microstrip and SIW-to-GCPW transition demonstrated to date.