High-Frequency Multi-Chip RF Module Enabled by Fused-Silica Stitch-Chip Technology: RF and Interconnect Characterization

A novel fused-silica stitch-chip technology for multichip RF modules is introduced, leveraging commercial off-the-shelf (COTS) components. This paper details the package assembly, RF characterization, and the implementation of stitchchips for die-to-die interconnects, which reduce signal loss relative to conventional approaches. A K/Ka-band low-noise amplifier (LNA) and a bare switch (SW) die are embedded in a custom package substrate and interconnected using stitch-chips. RF measurements show minimal LNA gain degradation ($<1 \text{dB}$) and a return loss greater than 12 dB, while the integrated LNA-SW module achieves a linear gain of 15 dB. The strainstress properties of the fabricated stitch-chip are verified, further proving its mechanical stability. Additionally, a potential cavityfree stitch-chip interconnect approach, enabling direct RF chain integration, is explored. This broadband and low-loss interconnect technology supports scalable chiplet integration and offers a promising solution for future high-frequency multi-chip RF systems.