innovation for industry
For Si-spin qubits, which are the focus of the Quantum Silicon Grenoble project, there are no strong superconducting requirements for the integration and packaging strategies and so for the choice of the interconnects, said Candice Thomas, one of the authors of the paper. The material constraints are less important than for superconducting qubits, thus a wider range of interconnects can be envisioned, such as SnAg microbumps and directly bonded Cu pads from Cu/SiO2 hybrid-bonding processes. SnAg microbumps have the advantage of being widely used in the 3D IC community, and the processes to fabricate them are well known at CEA-Leti with a state-of-the-art pitch as low as 20µm. The motivation to study Cu/SiO2 hybrid bonding lies in its high-resolution potential with a pitch as low as 1µm demonstrated at the institute with a wafer-to-wafer process.
Achieving Quantum Supremacy
The reliable operation
of these interconnect technologies offers two additional options to hybridize
chips with flip-chip processes for quantum computing or any other applications
requiring cryogenic temperatures, Thomas said. SnAg microbumps and direct Cu
bonded pads could be used for different parts of future quantum device packages,
depending especially on the needs in terms of pitch and on the type of chips to
This new packaging approach, designed for quantum-chip integration, paves the way for the large-scale integration of qubits, which is necessary to achieve quantum supremacy, Thomas continued. Direct bonding will allow us to go a step further in the large-scale integration strategy of Si-spin qubits.
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.