Development of Multilayer Readout Wiring for Large-Format TES X-Ray Microcalorimeter Arrays

Pursuing the feasibility of a large array of transition-edge sensors for future astrophysical missions, we have undertaken a study of multilayer readout wiring. It is composed of thin superconducting signal and return wires made of Al or Nb that sandwich an insulation SiO₂ film. Self and mutual inductances between signal and return wires of pixels, and also self fielding of bias leads can be reduced. Also a necessary spatial resource can be half compared to a normal wiring. We have fabricated four types of 20 × 20 wiring samples whose upper and lower wiring widths were 10 and 15 μm. High process yields of 95 ~ 97% were confirmed for all the four arrays in resistance measurements at room temperature. At low temperature, Al-Al samples showed sharp superconducting transitions, low residual resistances 1 ~ 2 mΩ, and high critical currents of >; 100 μA, which suggests that they can be used as our TES readout wiring. On the other hand, Nb-Al samples showed slow transitions and low critical currents ( <; 10 μA). Energy dispersive X-ray spectroscopy measurements indicated that impurities between Al and Nb films at electrical contacts influence these features.