Study on the enlargement of sensitive area of NIS-type tunnel junction detector

An idea for the enlargement of sensitive area of NIS (normal metal- insulator- superconductor) tunnel junction detectors is suggested and the fabrication procedure of NIS tunnel junction detectors described. An NIS tunnel junction detector consists of a normal metal X-ray absorber, insulator and superconductor trilayers. Ag is used for normal metal, Al2O3 for insulator and Nb for superconductor. We suggest a method to enlarge the sensitive area of NIS tunnel junction detector without deteriorating its energy resolution: we divide the absorber to several parts and connect them by superconductor leads. The heat capacity of each absorber is large. We utilize the fact that normal metal-superconductor connection does not conduct heat, but does electrically. In a sputtering chamber, three magnetrons for Ag, Al and Nb were installed to evaporate three metals without breaking vacuum. Using dc magnetron sputtering, superconductor Nb layer, insulator Al2O3 layer and normal metal Ag layer were evaporated on a sapphire substrate. A sapphire substrate was mounted on an X-Y stage. Four samples of Nb thin films became superconducting at 7.5 to 9 K (at 9.25 K for bulk Nb). (S.Y.)