A GaAs Four-Channel TRx Beamformer With Compact Size Based on Stacked-Chip Process

This letter introduces a compact 3-D stacked chip design for a four-channel RF TRx beamformer, emphasizing its innovative structure and performance attribute. The design leverages two layers of bonded Au micro-bumps and incorporates isolation piers between devices and channels, which are facilitated by the use of Au micro-bumps and gallium arsenide (GaAs) through substrate via. These isolation piers are specifically engineered to mitigate coupling, thereby significantly enhancing isolation. The 3-D stacked chip is formed through the vertical stacking of a CMOS chip, GaAs carrier, and GaAs monolithic microwave integrated circuit (MMIC) in a heterogeneous integration. This proposed 3-D stacked MMIC achieves a high level of integration within compact dimensions of $5.8\times 5.8\times 0.4$ mm. Across the entire operational bandwidth of 32–38 GHz, the transmitted signals reach an output power of 27 dBm, while the receiving channel demonstrates a noise figure (NF) of 3.5 dB. The measured results substantiate that the 3-D stacked MMIC offers exceptional reliability, superior performance, and feasibility for mass production.