A team of French scientists have collaborated with CEA-Leti’s experts to build a prototype interposer that meets the 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.
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.
“Realization of a QuIC3 demonstrator for 3D co-integration of quantum chips with CryoCMOS FDSOI 28nm control chips is an important step toward a full quantum computing system that operates at a very low temperature, less than 1 K, with optimum control and reading performance, said Maud Vinet, head of CEA-Leti’s quantum computing program.
“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”, Vinet said. The platform optimizes the control and readout of qubits by bringing the control electronics to the vicinity of the quantum chip without wire bonding.
“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.
The team included scientists at CEA-Leti, CEA-List and Néel Institute at the French National Centre for Scientific Research (CNRS).
The interposers’ primary purpose is to accommodate and connect quantum chips containing qubits and control chips and to address and read the qubits, with two metal levels on the front side of the interposers.
The QUI1 (Quantum Interposer n°1) mask set used to build the first interposer was designed during the Covid-19 confinement period by pooling the expertise of CEA-Leti, CEA-List and Néel Institute at CNRS.
In the coming months, the CEA-Leti, CEA-List and CNRS team will further investigate the integration of superconducting elements to optimize the properties of passive elements.
The collaboration will also include continued work on the 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.