Heterogeneous Integration of Microwave GaN Power Amplifiers With Si Matching Circuits

GaN high electron mobility transistors were integrated into monolithic microwave integrated circuits (MMICs) by molding hetero-substrates and using a redistribution layer (RDL). Driver amplifiers (DAs) and high-power amplifiers (HPAs) on SiC substrates were molded with matching circuits on Si substrates including Cu-filled through-substrate vias (TSVs), and their circuits on hetero-substrates were connected using a Cu RDL. This was the first attempt to fabricate hetero-substrate MMICs with five chips for two-stage power amplifiers. This method will be very useful to increase the achievable quantity of small DAs and HPAs—as opposed to using large MMICs with matching circuits on a SiC substrate—and to reduce production costs. Furthermore, various frequency bands, such as the millimeter-wave band, can be accommodated by changing the Si chips of the matching circuits.