Direct Die-to-Die Bridging for Heterogeneous mm-Wave Circuits Enabled by Fused-Silica Stitch-Chip Technology

This work presents a novel direct die-to-die (D2D) interconnect approach utilizing fused-silica stitch-chip technology to integrate heterogeneous commercial off-the-shelf (COTS) chiplets without the need for die embedding. This study evaluates RF performance through simulations and experimental measurements, comparing the stitch-chip interconnect against both wire-bond and other interconnect technologies. In addition, this study analyzes the impact of die embedding within a cavity on its performance. A heterogeneous integration of a low-noise amplifier (LNA) die (GaAs) and a switch die (AlGaAs), both designed for K-/Ka-band applications, is demonstrated using stitch-chip technology. RF characterization results verify that the bare LNA die maintains strong performance, achieving greater than 12-dB return loss (RL). The integrated LNA-switch module achieves a 20-dB linear gain up to 38 GHz, with the D2D stitch-chip interconnect showing a 4-dB improvement in gain compared to the die-to-package-to-die (D2P2D) approach and an 8.5-dB increase in gain compared to wire-bond connections. The results demonstrate that the proposed stitch-chip technology effectively minimizes insertion loss (IL), improves impedance matching, and enhances RF signal integrity, positioning it as an up-and-coming solution for future heterogeneous RF/mm-wave multichip integration applications.