Metal-Embedded Chiplet Assembly for Microwave Integrated Circuits

This letter provides an overview of the metal-embedded chiplet assembly for microwave integrated circuits (MECAMICs) technology. MECAMIC is a 2.5-D wafer-level packaging approach that provides seamless heterogeneous integration capabilities of compound semiconductor transistors (e.g., GaN HEMTs) with passive components and interconnects using a backside metal embedding process. The chiplets are embedded in through-interposer cavities, and the backside metallization locks the chiplets into position while providing dc and RF ground for the high-frequency circuits. With this hybrid manufacturing approach, high-performance RF ICs can: 1) be designed using the best transistor technology for the function; 2) be fabricated in short cycle times through hybrid manufacturing; and 3) compete performancewise with monolithic circuits. We demonstrated an $X$ -band power amplifier circuit realized in MECAMIC with a saturated output power of 31 dB and a peak power added efficiency of 54%, which compared favorably to its monolithic GaN monolithic microwave integrated circuit (MMIC) counterpart. The MECAMIC process cycle time was $4.5\times $ faster than the monolithic process.