A D-Band 24-dBm MMIC Amplifier by Innovative Power Combining of GaN HEMTs in a SiC SIW

Conventional power combiners based on microstrip or coplanar transmission lines are hindered by high loss above 110 GHz. By contrast, power combiners based on substrate-integrated waveguides (SIWs) can have low loss, high-power capacity, and minimum crosstalk at the same frequencies. Recently, we demonstrated a D-band (110–170 GHz) distributed amplifier by embedding transistors in the middle of an SIW as voltage probes. The voltage probes are realized through hot through-substrate vias (TSVs), which are not supported by all semiconductor foundries. As an alternative, this work embeds transistors along the sidewalls of an SIW as current probes through standard TSVs grounded to the backside metal layer. The new approach combines twice as many transistors per unit length of the SIW without requiring either hot TSVs or interconnects from the sidewalls to the middle of the SIW. This results in order-of-magnitude improvement in the power amplifier. For example, the measured output power of the new distributed amplifier at 145 GHz is 24 dBm with an associated power added efficiency of 9%, making its performance approaching state-of-the-art InP and SiGe D-band power amplifiers. Since the innovative power-combing approach is material agnostic and device agnostic, it can also be used to improve the performance of InP and SiGe power amplifiers above 110 GHz.