Superconducting Thin-Film Interconnects for Cryogenic Photon Detector Arrays

Next generation astrophysical observatories need improvements in readout electronics and associated high density interconnects. In particular, advanced imaging spectrometers for x-ray astronomy will require significant improvements in the high density interconnects between the detector arrays and the first stage electronics. These detectors operate at 50 to 100 mK, while the first stage is held between 1.3 and 1.5 K. Interconnects are needed that provide the required signal paths while imparting a total thermal heat load on the detector stage of less than 0.5 microwatts. The innovation proposed to meet this need is an ultra-thin polyimide membrane supporting a high-density array of vacuum-deposited superconducting traces. During Phase I, 100-trace Niobium arrays were deposited on ultra-thin polyimide films. The critical current density (Jc) averaged 2.1 x 106 A/cm2, exceeding Phase I goals and demonstrating the feasibility of the innovation. This result suggests that interconnects with 1000 traces are feasible within specified heat load limits and the goal of Phase II will be to produce such interconnects for both NASA and commercial applications. The proposed interconnects greatly broaden the thermal budget/signal capacity envelope for low-temperature detector applications by combining existing lithographic technology with Luxel's state-of-the-art thin film processes and mission tested polyimide.