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

Pursuing the feasibility of a large array of transitionedge 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 SiO(2) 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 x 20 wiring samples whose upper and lower wiring widths were 10 and 15 mu m. High process yields of 95 similar to 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 similar to 2 m Omega, and high critical currents of 1 similar to 100 mu A, 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 mu A). Energy dispersive X-ray spectroscopy measurements indicated that impurities between Al and Nb films at electrical contacts influence these features.