3D integration of superconducting quantum systems – part 2: Interposer tier with superconducting TSVs and qubits*

As quantum systems reach the scale needed for a broad range of quantum computing applications, engineers are addressing the challenge of developing robust systems-level readout and control of multi-qubit systems. The interposer in the 3-stack integration approach provides access to multi-level superconducting circuitry through superconducting through-silicon vias (TSVs) while preserving qubit performance by isolating the qubits from lossy dielectrics in the routing tier. Our active interposer also provides additional levels for resonators and qubits to be integrated into the system and enables novel circuit elements that incorporate TSVs. We present our fabrication process for this active interposer tier, as well as characterization data for superconducting TSVs and qubits.