Metal-Embedded Chip Assembly Processing for Enhanced RF Circuit Performance

This paper presents the radio frequency (RF) benefits of a heterogeneous integration technique for multi-chip modules. Passive components, such as lumped metal-insulator-semiconductor (MIS) and ceramic capacitors, as well as coupler circuits implemented on alumina substrates, are integrated in a metal-embedded chip assembly (MECA) process together with GaN monolithic microwave-integrated circuits (MMICs) in a way that provides a common RF and thermal ground. Simulations show that photolithographically defined interconnects can outperform wire bonds from 10 to 100 GHz. The interconnect layer of the MECA process forms bridge transmission lines with lower loss and comparable dispersion to microstrip lines, and with 35% higher characteristic impedances, validated by measurements up to 25 GHz. Microstrip Lange and branch-line couplers are designed partially on alumina and completed with MECA interconnects during the integration process, resulting in good performance in agreement with simulations. Finally, measurements of a GaN power amplifier (PA) MMIC integrated into the MECA process show gain and power-added efficiency (PAE) improvements of up to 3 dB and 3.2 percentage points, respectively.