Material Properties of a Low Contraction and Resistivity Silicon–Aluminum Composite for Cryogenic Detectors

We report on the cryogenic properties of a low-contraction silicon–aluminum composite, namely Japan Fine Ceramics SA001, to use as a packaging structure for cryogenic silicon devices. SA001 is silicon–aluminum composite material (75% silicon by volume) and has a low thermal expansion coefficient ( ∼ 1/3 that of aluminum). The superconducting transition temperature of SA001 is measured to be 1.18 K, which is in agreement with that of pure aluminum and is thus available as a superconducting magnetic shield material. The residual resistivity of SA001 is 0.065 µΩm, which is considerably lower than equivalent silicon–aluminum composite material. The measured thermal contraction of SA001 immersed in liquid nitrogen is L 293 K - L 77 K L 293 K = 0.12 % , which is consistent with the expected rate obtained from the volume-weighted mean of the contractions of silicon and aluminum. The machinability of SA001 is also confirmed with a demonstrated fabrication of a conical feedhorn array, with a wall thickness of 100 µm. These properties are suitable for packaging applications for large-format superconducting detector devices.