Accurate gap control of 3D-integrated superconducting quantum circuits using asymmetric indium architecture and multi-angle flip-chip bonding
The study investigates flip-chip bonding for 3D superconducting qubits using an asymmetric indium architecture: thick 20 µm bumps on the control chip and thin 200 nm pads on the qubit chip. By combining this architecture with a multi-angle compression procedure, researchers achieved a low post-bonding tilt of (20±12) µrad. This method preserves transmon coherence, yielding T1 times comparable to planar devices, establishing a robust path for scalable 3D quantum processors.