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MON: Monday Contributed Sessions

MON 14: QIP Implementations: Solid-State Devices I

MON 14.4: Vortrag

Montag, 8. September 2025, 17:15–17:30, ZHG002

Optimized flip chip bonding for 3D integrated superconducting quantum circuits — •Lea Richard^{1, 2}, Julius Feigl^{1, 2}, Niklas Bruckmoser^{1, 2}, Leon Koch^{1, 2}, Lasse Södergen^{1, 2}, and Stefan Filipp^{1, 2} — ¹Technical University of Munich — ²Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften

In order to use quantum computing to tackle classically intractable problems, quantum processors must grow to larger scales. Yet, in current planar architectures, routing multiple lines to an increasing number of qubits while minimizing crosstalk remains a significant challenge. 3D-integration techniques, such as flip-chip bonding enable more efficient connectivity. However, implementing a novel circuit geometry introduces challenges, including maintaining high coherence and preserving precise parameter targeting. Flip-chip bonding relies on indium bump bonds to mechanically and galvanically connect two separate chips. The additional fabrication steps can lead to new loss channels and degrade overall system performance. Moreover, in superconducting quantum circuits, capacitances and inductances are determined by the design of the electrodes. In a flip-chip assembly, these parameters depend on the gap separating the bonded chips and variations during the bonding process can limit accurate parameter targeting. To address these challenges, we present the fabrication of high-thickness indium bumps and the development of an optimized flip-chip bonding process for high-coherence quantum circuits. Additionally, we introduce a method for improving interchip spacing control and parameter targeting using polymer spacers.

Keywords: Quantum Computing; Flip chip bonding; Indium bump; Qubit