A 220-340 GHz Modified Marchand Balun with Asymmetric Ground Shield in 90 nm SiGe-BiCMOS

This work presents a modified Marchand balun operating in the 220-340 GHz frequency range. By introducing an asymmetric ground shield in the coupler sections, the proposed design achieves low amplitude and phase imbalance. The design is well suited for on-wafer testing of structures such as differential power amplifiers and differential slot antennas radiating through the Silicon substrate. A prototype is fabricated in a 90 nm SiGe-BiCMOS process and is characterized in the 200-325 GHz range, showing good agreement with simulation. The measured amplitude and phase imbalance are 0.1 dB and 1 degree at 270 GHz, remaining lower than ± 1 dB and ± 3 degrees respectively in the 240-290 GHz frequency range.