A team of French scientists has started to build a prototype interposer that meets requirements of quantum computing by allowing integration and testing of both quantum and control chips fabricated from different materials and technologies and coming from different partners, according to a news release.
Known as QuIC3, which stands for quantum integrated circuits with CryoCMOS, the prototype demonstrator controls quantum chips by embedding control electronics near the quantum chip inside a dilution cryostat at T<1K. This temperature range is required for reliable operation of qubits, the fundamental or logic units of quantum computers. The demonstrator is made from an interposer in silicon on which quantum chips and control electronics are integrated by 3D flip-chip processes. The control electronics are fabricated on standard FDSOI 28nm-node technology and manufactured by STMicroelectronics.
The team included scientists at CEA-Leti, CEA-List and Néel Institute at the French National Centre for Scientific Research (CNRS).
“This interposer breakthrough is a unique combination of expertise on quantum physics, 3D technologies, material integration, IC interface, passives design and micro-architecture to achieve a solution adapted to quantum computation.”
This proximity of the control electronics and the qubits increases the number of qubits that can be controlled, because it avoids the limitation on the number of lines of the cryostat. Wire bonding is not necessary because the qubits and control electronics are coupled by routing lines on the interposer, which reduces parasitic capacitance and inductance that complicate measurements.
The platform created by the interposer also can allow thermal decoupling of the quantum and control chips to keep the quantum chip at the lowest temperature possible.
In the coming months, the CEA-Leti, CEA-List and CNRS team will further investigate integration of superconducting elements to optimize the properties of passive elements. The collaboration will also include continued work on fabrication of the interposer, quantum chips and control-electronics chips. Once all the bricks are ready and assembled, the quantum and control chips will be flipped and hybridized on the interposer, followed by electrical measurements at low temperatures of the multi-chip assemblies. The final full interposer prototype is expected in 2021.
All of these elements aim to reach very large-scale integration of qubits,” Vinet added.
Next generations of the interposer will incorporate through silicon vias (TSV) to increase the connection density and eliminate wire bonding.