Design of Chip-to-Waveguide Transition Centered at 220 GHz for sub-THz Packaging

A contactless chip-to-waveguide transition suitable for SiGe monolithic microwave integrated circuits (MMIC) packaging at 220 GHz is presented in this paper. The core part of the back-to-back (B2B) transition is an on-chip radiation aperture coupled to WR-3.4 metal waveguide, with quarter-wavelength waveguide steps for impedance matching. A gap between two waveguide lids is introduced for the leakage of waveguide through mode, while in ideal chipless simulation the narrow gap cannot support enough suppression. For better performance estimation during B2B design process, on-chip transmission line is damaged to verify the transition characteristic and the B2B structure is checked in half as single side chip-to-waveguide transition for performance validation. Measured results show cascaded half B2B structure gives better agreement. The whole B2B transition has 3-dB bandwidth of 198.4-244.1 GHz and 7.5 dB insertion loss at center frequency without deembedding.