Superconducting Through-Silicon Coplanar Waveguide Interconnects for High-Bandwidth Three-Dimensional Integration

Superconducting digital integrated circuits (ICs) are driving increasing demand for low-loss, high-bandwidth vertical interconnects to support advanced cryogenic systems. In this work, broadband superconducting through-silicon coplanar waveguides (CPWs) are fabricated within wet-etched vias by sputtering and patterning niobium (Nb) on the via sidewalls, establishing an effective architecture for high-frequency vertical signal transmission. By systematically optimizing the CPW geometry and introducing sidewall transition compensation within the via, the proposed structure mitigates impedance discontinuities and enhances transmission performance. Experimental measurements demonstrate stable broadband operation, with S₁₁ ≤ −15 dB and S₂₁ ≥ −3.5 dB from 0.01 to 48 GHz. De-embedded results further indicate that a single through-silicon CPW achieves S₁₁​ ≤ −15 dB and S₂₁ ≥ −1 dB up to 37 GHz, confirming low reflection and reduced transmission loss in the via region. These results demonstrate the feasibility of superconducting through-silicon CPWs as high-bandwidth vertical interconnects and provide a scalable pathway toward three-dimensional integration in superconducting computing and cryogenic microwave systems.