Wu, J., Gourikutty, S. B. N., Lim, T. G., & Bhattacharya, S. (2026). Vertical Interconnects Characterization for 448 Gbps/lane Co-Packaged Optics using Double-Sided Probing Method. In (Editor), 2026 IEEE 76th Electronic Components and Technology Conference (ECTC). https://doi.org/10.1109/ectc51846.2026.00144
Abstract:
Co-Packaged Optics (CPO) shortens the electrical distance between optical engines (OEs) and switch ASICs to overcome electrical I/O bottlenecks for next-generation AI systems, driving the need for 448 Gb/s/lane PAM4 electrical interconnects with bandwidth approaching 110 GHz. This work characterizes and compares four vertical interconnect technologies for OE I/O routing: a substrate-based via (SUB-VIA), Through-Mold Via (TMV), Through-Silicon Via (TSV), and Through-Glass Via (TGV). RF performance is measured using a direct double-sided probing method to obtain S-parameters, avoiding the accuracy and bandwidth limitations of conventional back-to-back de-embedding. Single-ended GSG TSV and TGV are measured up to 110 GHz, while GSG SUB-VIA and GSSG differential TMV transition are measured up to 65 GHz and 50 GHz, respectively. 3D full-wave EM models are developed and show good agreement with measurements over the respective frequency bands. Based on the measurement-calibrated simulation models, GSSG differential OE I/O transitions from EIC to package substrate are designed and simulated. All transitions maintain >10 dB return loss from DC to 120 GHz, with simulated insertion loss at 112 GHz of 0.60 dB (SUB-VIA), 0.87 dB (TMV), 0.37 dB (TSV), and 0.13 dB (TGV). Time-domain simulations at 448 Gb/s PAM4 show clear eye openings without Tx/Rx amplification/equalization, with TGV and TSV achieving the best margins. These results identify TGV as a strong candidate for future high-density 448 Gb/s/lane CPO electrical I/O routing.
License type:
Publisher Copyright
Funding Info:
This research / project is supported by the A*STAR - IME-Applied Centre of Excellence in Advanced Packaging 3.0 (Packaging 3.0)
Grant Reference no. : H21-MCP0080 / (old) I2101E0008