New way to manage high density signal connections and the small power of sub-K cryo-generators

The small power of cryo-generators at sub-K temperature is a strong bottleneck for large sub-K experiments, such as large spatial spectro-imagers for astrophysics, or qubits arrays for quantic computing. It is even very often the limitation to the number of channels of the experiments.To tackle this, we have developed a very innovative hybridization technology allowing the interconnections, by a large number of links, of two devices (typically a sub-K detector and the first stage of its readout electronics) cooled at different temperatures (typically 50 mK and 0.3 – 1 K). These hybridizations present a very low electrical resistance and an extremely high thermal resistance, unmatched by existing technologies, thanks to a multilayer superconducting metallization technology.The very low thermal conduction (much lower than the phonon conduction in a homogeneous superconducting material) is obtained thanks to an acoustic mismatch between layers. The link is ultra-compact (≃ μm) and with ultra-low electrical impedance thanks to the use of superconducting materials only. It can be used to interconnect devices, for example when associated with ball hybridization, or inside the elementary cells of low temperature detectors, for example to separate the two functions of absorption and thermometry. So this new process could transform drastically, in the future, the architecture of nearly all sub-K instrumentations.We have already realized such device at the Plateforme Technologique Amont (PTA) Grenoble facility. Measurements in the sub-K range demonstrate very interesting thermal performances. In this paper, we present the principle behind this thermal property of this Multi-Layer, the first results, and the perspectives.