Nb3Al paste for superconducting connections

Abstract

We achieved a superconducting transition temperature of 9 K in a superconducting paste prepared using Nb3Al particles. The paste was synthesized by a simple traditional method often used to prepare Ag paste. Subsequently, the paste was screen printed on a solid substrate and thermally cured under optimum conditions to form a single-phase film with a thickness of 150 µm. The single-phase nature of the Nb3Al film was confirmed by X-ray diffraction, and the close contact of each Nb3Al particle with its neighboring particles was confirmed by cross-sectional scanning electron microscopy. The resistivity of this thick Nb3Al film is zero at temperatures lower than 9 K, indicating that this film is superconducting at cryogenic temperatures. Furthermore, NbTi-thin-film-pad/Nb3Al/NbTi-thin-film-pad connections were fabricated by vapor-phase growth and screen printing. The temperature dependence of the connection resistivity showed two superconducting transitions: a gradual decrease in resistivity from 13 K to 9 K, attributed to Nb3Al, and a sharp decrease at 6.2 K, attributed to the superconducting transition of the NbTi thin film. These results indicated that the Nb3Al superconducting paste is a candidate for achieving superconducting-thin-film-based device-to-device integration technology comprising three elements, namely superconducting wires, a superconducting crossover, and a superconducting contact.